Adding upstream version 14.2.21.upstream/14.2.21upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

61 files changed, 8541 insertions, 0 deletions

diff --git a/src/crimson/CMakeLists.txt b/src/crimson/CMakeLists.txt
new file mode 100644
index 00000000..d7b58521
--- /dev/null
+++ b/src/crimson/CMakeLists.txt
@@ -0,0 +1,141 @@
+add_library(crimson::cflags INTERFACE IMPORTED)
+set_target_properties(crimson::cflags PROPERTIES
+  INTERFACE_COMPILE_DEFINITIONS "WITH_SEASTAR=1"
+  INTERFACE_LINK_LIBRARIES Seastar::seastar)
+
+set(crimson_common_srcs
+  common/config_proxy.cc
+  common/perf_counters_collection.cc
+  common/assert.cc
+  common/log.cc)
+
+# the specialized version of ceph-common, where
+#  - the logging is sent to Seastar backend
+#  - and the template parameter of lock_policy is SINGLE
+add_library(crimson-common STATIC
+  ${PROJECT_SOURCE_DIR}/src/common/admin_socket.cc
+  ${PROJECT_SOURCE_DIR}/src/common/admin_socket_client.cc
+  ${PROJECT_SOURCE_DIR}/src/common/bit_str.cc
+  ${PROJECT_SOURCE_DIR}/src/common/bloom_filter.cc
+  ${PROJECT_SOURCE_DIR}/src/common/ceph_argparse.cc
+  ${PROJECT_SOURCE_DIR}/src/common/ceph_context.cc
+  ${PROJECT_SOURCE_DIR}/src/common/ceph_crypto.cc
+  ${PROJECT_SOURCE_DIR}/src/common/ceph_hash.cc
+  ${PROJECT_SOURCE_DIR}/src/common/ceph_time.cc
+  ${PROJECT_SOURCE_DIR}/src/common/ceph_strings.cc
+  ${PROJECT_SOURCE_DIR}/src/common/cmdparse.cc
+  ${PROJECT_SOURCE_DIR}/src/common/common_init.cc
+  ${PROJECT_SOURCE_DIR}/src/common/compat.cc
+  ${PROJECT_SOURCE_DIR}/src/common/code_environment.cc
+  ${PROJECT_SOURCE_DIR}/src/common/config.cc
+  ${PROJECT_SOURCE_DIR}/src/common/config_values.cc
+  ${PROJECT_SOURCE_DIR}/src/common/dout.cc
+  ${PROJECT_SOURCE_DIR}/src/common/entity_name.cc
+  ${PROJECT_SOURCE_DIR}/src/common/environment.cc
+  ${PROJECT_SOURCE_DIR}/src/common/errno.cc
+  ${PROJECT_SOURCE_DIR}/src/common/escape.cc
+  ${PROJECT_SOURCE_DIR}/src/common/hex.cc
+  ${PROJECT_SOURCE_DIR}/src/common/fs_types.cc
+  ${PROJECT_SOURCE_DIR}/src/common/histogram.cc
+  ${PROJECT_SOURCE_DIR}/src/common/hobject.cc
+  ${PROJECT_SOURCE_DIR}/src/common/hostname.cc
+  ${PROJECT_SOURCE_DIR}/src/common/ipaddr.cc
+  ${PROJECT_SOURCE_DIR}/src/common/lockdep.cc
+  ${PROJECT_SOURCE_DIR}/src/common/mutex_debug.cc
+  ${PROJECT_SOURCE_DIR}/src/common/mempool.cc
+  ${PROJECT_SOURCE_DIR}/src/common/options.cc
+  ${PROJECT_SOURCE_DIR}/src/common/perf_counters.cc
+  ${PROJECT_SOURCE_DIR}/src/common/perf_histogram.cc
+  ${PROJECT_SOURCE_DIR}/src/common/page.cc
+  ${PROJECT_SOURCE_DIR}/src/common/pick_address.cc
+  ${PROJECT_SOURCE_DIR}/src/common/snap_types.cc
+  ${PROJECT_SOURCE_DIR}/src/common/signal.cc
+  ${PROJECT_SOURCE_DIR}/src/common/str_list.cc
+  ${PROJECT_SOURCE_DIR}/src/common/str_map.cc
+  ${PROJECT_SOURCE_DIR}/src/common/strtol.cc
+  ${PROJECT_SOURCE_DIR}/src/common/reverse.c
+  ${PROJECT_SOURCE_DIR}/src/common/types.cc
+  ${PROJECT_SOURCE_DIR}/src/common/utf8.c
+  ${PROJECT_SOURCE_DIR}/src/common/version.cc
+  ${PROJECT_SOURCE_DIR}/src/common/BackTrace.cc
+  ${PROJECT_SOURCE_DIR}/src/common/ConfUtils.cc
+  ${PROJECT_SOURCE_DIR}/src/common/DecayCounter.cc
+  ${PROJECT_SOURCE_DIR}/src/common/HTMLFormatter.cc
+  ${PROJECT_SOURCE_DIR}/src/common/Formatter.cc
+  ${PROJECT_SOURCE_DIR}/src/common/Graylog.cc
+  ${PROJECT_SOURCE_DIR}/src/common/LogEntry.cc
+  ${PROJECT_SOURCE_DIR}/src/common/Mutex.cc
+  ${PROJECT_SOURCE_DIR}/src/common/SubProcess.cc
+  ${PROJECT_SOURCE_DIR}/src/common/TextTable.cc
+  ${PROJECT_SOURCE_DIR}/src/common/Thread.cc
+  ${PROJECT_SOURCE_DIR}/src/common/HeartbeatMap.cc
+  ${PROJECT_SOURCE_DIR}/src/common/PluginRegistry.cc
+  ${PROJECT_SOURCE_DIR}/src/librbd/Features.cc
+  ${PROJECT_SOURCE_DIR}/src/log/Log.cc
+  ${PROJECT_SOURCE_DIR}/src/mgr/ServiceMap.cc
+  ${PROJECT_SOURCE_DIR}/src/mds/inode_backtrace.cc
+  ${PROJECT_SOURCE_DIR}/src/mds/mdstypes.cc
+  ${PROJECT_SOURCE_DIR}/src/mds/FSMap.cc
+  ${PROJECT_SOURCE_DIR}/src/mds/FSMapUser.cc
+  ${PROJECT_SOURCE_DIR}/src/mds/MDSMap.cc
+  ${PROJECT_SOURCE_DIR}/src/msg/msg_types.cc
+  ${PROJECT_SOURCE_DIR}/src/msg/Message.cc
+  ${PROJECT_SOURCE_DIR}/src/mon/PGMap.cc
+  ${PROJECT_SOURCE_DIR}/src/mon/MonCap.cc
+  ${PROJECT_SOURCE_DIR}/src/mon/MonMap.cc
+  ${PROJECT_SOURCE_DIR}/src/osd/osd_types.cc
+  ${PROJECT_SOURCE_DIR}/src/osd/ECMsgTypes.cc
+  ${PROJECT_SOURCE_DIR}/src/osd/HitSet.cc
+  ${PROJECT_SOURCE_DIR}/src/osd/OSDMap.cc
+  ${PROJECT_SOURCE_DIR}/src/osd/PGPeeringEvent.cc
+  ${crimson_common_srcs}
+  $<TARGET_OBJECTS:crimson-auth>
+  $<TARGET_OBJECTS:common_buffer_obj>
+  $<TARGET_OBJECTS:common_mountcephfs_objs>
+  $<TARGET_OBJECTS:crimson-crush>
+  $<TARGET_OBJECTS:global_common_objs>)
+
+target_compile_definitions(crimson-common PRIVATE
+  "CEPH_LIBDIR=\"${CMAKE_INSTALL_FULL_LIBDIR}\""
+  "CEPH_PKGLIBDIR=\"${CEPH_INSTALL_FULL_PKGLIBDIR}\""
+  "CEPH_DATADIR=\"${CEPH_INSTALL_DATADIR}\"")
+
+target_link_libraries(crimson-common
+  PUBLIC
+    json_spirit
+  PRIVATE
+    crc32
+    crimson::cflags
+    Boost::iostreams
+    Boost::random
+    ${NSS_LIBRARIES} ${NSPR_LIBRARIES} OpenSSL::Crypto)
+
+set(crimson_auth_srcs
+  auth/KeyRing.cc)
+set(crimson_mon_srcs
+  mon/MonClient.cc
+  ${PROJECT_SOURCE_DIR}/src/mon/MonSub.cc)
+set(crimson_net_srcs
+  net/Dispatcher.cc
+  net/Errors.cc
+  net/Messenger.cc
+  net/SocketConnection.cc
+  net/SocketMessenger.cc
+  net/Socket.cc)
+set(crimson_thread_srcs
+  thread/ThreadPool.cc
+  thread/Throttle.cc)
+add_library(crimson STATIC
+  ${crimson_auth_srcs}
+  ${crimson_mon_srcs}
+  ${crimson_net_srcs}
+  ${crimson_thread_srcs}
+  ${CMAKE_SOURCE_DIR}/src/common/buffer_seastar.cc)
+target_compile_options(crimson PUBLIC
+  "-ftemplate-backtrace-limit=0")
+target_link_libraries(crimson
+  PUBLIC
+    crimson-common
+    crimson::cflags)
+add_subdirectory(os)
+add_subdirectory(osd)
diff --git a/src/crimson/auth/Errors.cc b/src/crimson/auth/Errors.cc
new file mode 100644
index 00000000..c5f1b8d8
--- /dev/null
+++ b/src/crimson/auth/Errors.cc
@@ -0,0 +1,31 @@
+#include "Errors.h"
+
+namespace ceph::net {
+
+const std::error_category& auth_category()
+{
+  struct category : public std::error_category {
+    const char* name() const noexcept override {
+      return "ceph::auth";
+    }
+
+    std::string message(int ev) const override {
+      switch (static_cast<error>(ev)) {
+        case error::success:
+          return "success",
+        case error::key_not_found:
+          return "key not found";
+        case error::invalid_key:
+          return "corrupted key";
+        case error::unknown_service:
+          return "unknown service";
+        default:
+          return "unknown";
+      }
+    }
+  };
+  static category instance;
+  return instance;
+}
+
+} // namespace ceph::auth
diff --git a/src/crimson/auth/Errors.h b/src/crimson/auth/Errors.h
new file mode 100644
index 00000000..92f5c733
--- /dev/null
+++ b/src/crimson/auth/Errors.h
@@ -0,0 +1,37 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+
+#pragma once
+
+namespace ceph::auth {
+
+enum class error {
+  success = 0,
+  key_not_found,
+  invalid_key,
+  unknown_service, // no ticket handler for required service
+};
+
+const std::error_category& auth_category();
+
+inline std::error_code make_error_code(error e)
+{
+  return {static_cast<int>(e), auth_category()};
+}
+
+inline std::error_condition make_error_condition(error e)
+{
+  return {static_cast<int>(e), auth_category()};
+}
+
+class auth_error : public std::runtime_error {};
+
+} // namespace ceph::auth
+
+namespace std {
+
+/// enables implicit conversion to std::error_condition
+template <>
+struct is_error_condition_enum<ceph::auth::error> : public true_type {};
+
+} // namespace std
diff --git a/src/crimson/auth/KeyRing.cc b/src/crimson/auth/KeyRing.cc
new file mode 100644
index 00000000..5f82a262
--- /dev/null
+++ b/src/crimson/auth/KeyRing.cc
@@ -0,0 +1,89 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*- 
+// vim: ts=8 sw=2 smarttab
+
+#include "KeyRing.h"
+
+#include <boost/algorithm/string.hpp>
+
+#include <seastar/core/do_with.hh>
+#include <seastar/core/fstream.hh>
+#include <seastar/core/future-util.hh>
+#include <seastar/core/reactor.hh>
+
+#include "common/buffer_seastar.h"
+#include "auth/KeyRing.h"
+#include "include/denc.h"
+#include "crimson/common/config_proxy.h"
+
+namespace ceph::auth {
+
+seastar::future<seastar::temporary_buffer<char>> read_file(const std::string& path)
+{
+  return seastar::open_file_dma(path, seastar::open_flags::ro).then([] (seastar::file f) {
+    return f.size().then([f = std::move(f)](size_t s) {
+      return seastar::do_with(seastar::make_file_input_stream(f), [s](seastar::input_stream<char>& in) {
+        return in.read_exactly(s);
+      });
+    });
+  });
+}
+
+seastar::future<KeyRing*> load_from_keyring(KeyRing* keyring)
+{
+  std::vector<std::string> paths;
+  boost::split(paths, ceph::common::local_conf()->keyring,
+               boost::is_any_of(",;"));
+  std::pair<bool, std::string> found;
+  return seastar::map_reduce(paths, [](auto path) {
+    return seastar::engine().file_exists(path).then([path](bool file_exists) {
+      return std::make_pair(file_exists, path);
+    });
+  }, std::move(found), [](auto found, auto file_exists_and_path) {
+    if (!found.first && file_exists_and_path.first) {
+      found = std::move(file_exists_and_path);
+    }
+    return found;
+  }).then([keyring] (auto file_exists_and_path) {
+    const auto& [exists, path] = file_exists_and_path;
+    if (exists) {
+      return read_file(path).then([keyring](auto buf) {
+        bufferlist bl;
+        bl.append(buffer::create(std::move(buf)));
+        auto i = bl.cbegin();
+        keyring->decode(i);
+        return seastar::make_ready_future<KeyRing*>(keyring);
+      });
+    } else {
+      return seastar::make_ready_future<KeyRing*>(keyring);
+    }
+  });
+}
+
+seastar::future<KeyRing*> load_from_keyfile(KeyRing* keyring)
+{
+  auto& path = ceph::common::local_conf()->keyfile;
+  if (!path.empty()) {
+    return read_file(path).then([keyring](auto buf) {
+      EntityAuth ea;
+      ea.key.decode_base64(std::string(buf.begin(),
+                                       buf.end()));
+      keyring->add(ceph::common::local_conf()->name, ea);
+      return seastar::make_ready_future<KeyRing*>(keyring);
+    });
+  } else {
+    return seastar::make_ready_future<KeyRing*>(keyring);
+  }
+}
+
+seastar::future<KeyRing*> load_from_key(KeyRing* keyring)
+{
+  auto& key = ceph::common::local_conf()->key;
+  if (!key.empty()) {
+    EntityAuth ea;
+    ea.key.decode_base64(key);
+    keyring->add(ceph::common::local_conf()->name, ea);
+  }
+  return seastar::make_ready_future<KeyRing*>(keyring);
+}
+
+} // namespace ceph::auth
diff --git a/src/crimson/auth/KeyRing.h b/src/crimson/auth/KeyRing.h
new file mode 100644
index 00000000..b68e6389
--- /dev/null
+++ b/src/crimson/auth/KeyRing.h
@@ -0,0 +1,15 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*- 
+// vim: ts=8 sw=2 smarttab
+
+#pragma once
+
+#include <seastar/core/future.hh>
+
+class KeyRing;
+
+namespace ceph::auth {
+  // see KeyRing::from_ceph_context
+  seastar::future<KeyRing*> load_from_keyring(KeyRing* keyring);
+  seastar::future<KeyRing*> load_from_keyfile(KeyRing* keyring);
+  seastar::future<KeyRing*> load_from_key(KeyRing* keyring);
+}
diff --git a/src/crimson/common/assert.cc b/src/crimson/common/assert.cc
new file mode 100644
index 00000000..9ed6b7e3
--- /dev/null
+++ b/src/crimson/common/assert.cc
@@ -0,0 +1,56 @@
+#include <cstdarg>
+
+#include <seastar/util/backtrace.hh>
+#include <seastar/core/reactor.hh>
+
+#include "include/ceph_assert.h"
+
+#include "crimson/common/log.h"
+
+namespace ceph {
+  [[gnu::cold]] void __ceph_assert_fail(const ceph::assert_data &ctx)
+  {
+    __ceph_assert_fail(ctx.assertion, ctx.file, ctx.line, ctx.function);
+  }
+
+  [[gnu::cold]] void __ceph_assert_fail(const char* assertion,
+                                        const char* file, int line,
+                                        const char* func)
+  {
+    seastar::logger& logger = ceph::get_logger(0);
+    logger.error("{}:{} : In function '{}', ceph_assert(%s)\n"
+                 "{}",
+                 file, line, func, assertion,
+                 seastar::current_backtrace());
+    abort();
+  }
+  [[gnu::cold]] void __ceph_assertf_fail(const char *assertion,
+                                         const char *file, int line,
+                                         const char *func, const char* msg,
+                                         ...)
+  {
+    char buf[8096];
+    va_list args;
+    va_start(args, msg);
+    std::vsnprintf(buf, sizeof(buf), msg, args);
+    va_end(args);
+
+    seastar::logger& logger = ceph::get_logger(0);
+    logger.error("{}:{} : In function '{}', ceph_assert(%s)\n"
+                 "{}",
+                 file, line, func, assertion,
+                 seastar::current_backtrace());
+    abort();
+  }
+
+  [[gnu::cold]] void __ceph_abort(const char* file, int line,
+                                  const char* func, const std::string& msg)
+  {
+    seastar::logger& logger = ceph::get_logger(0);
+    logger.error("{}:{} : In function '{}', abort(%s)\n"
+                 "{}",
+                 file, line, func, msg,
+                 seastar::current_backtrace());
+    abort();
+  }
+}
diff --git a/src/crimson/common/config_proxy.cc b/src/crimson/common/config_proxy.cc
new file mode 100644
index 00000000..720fcffd
--- /dev/null
+++ b/src/crimson/common/config_proxy.cc
@@ -0,0 +1,45 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+
+#include "config_proxy.h"
+
+namespace ceph::common {
+
+ConfigProxy::ConfigProxy(const EntityName& name, std::string_view cluster)
+{
+  if (seastar::engine().cpu_id() != 0) {
+    return;
+  }
+  // set the initial value on CPU#0
+  values.reset(seastar::make_lw_shared<ConfigValues>());
+  values.get()->name = name;
+  values.get()->cluster = cluster;
+  // and the only copy of md_config_impl<> is allocated on CPU#0
+  local_config.reset(new md_config_t{*values, obs_mgr, true});
+  if (name.is_mds()) {
+    local_config->set_val_default(*values, obs_mgr,
+				  "keyring", "$mds_data/keyring");
+  } else if (name.is_osd()) {
+    local_config->set_val_default(*values, obs_mgr,
+				  "keyring", "$osd_data/keyring");
+  }
+}
+
+seastar::future<> ConfigProxy::start()
+{
+  // populate values and config to all other shards
+  if (!values) {
+    return seastar::make_ready_future<>();
+  }
+  return container().invoke_on_others([this](auto& proxy) {
+    return values.copy().then([config=local_config.get(),
+			       &proxy](auto foreign_values) {
+      proxy.values.reset();
+      proxy.values = std::move(foreign_values);
+      proxy.remote_config = config;
+      return seastar::make_ready_future<>();
+    });
+  });
+}
+
+ConfigProxy::ShardedConfig ConfigProxy::sharded_conf;
+}
diff --git a/src/crimson/common/config_proxy.h b/src/crimson/common/config_proxy.h
new file mode 100644
index 00000000..46690009
--- /dev/null
+++ b/src/crimson/common/config_proxy.h
@@ -0,0 +1,178 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+
+#pragma once
+
+#include <seastar/core/reactor.hh>
+#include <seastar/core/sharded.hh>
+#include "common/config.h"
+#include "common/config_obs.h"
+#include "common/config_obs_mgr.h"
+#include "common/errno.h"
+
+namespace ceph::common {
+
+// a facade for managing config. each shard has its own copy of ConfigProxy.
+//
+// In seastar-osd, there could be multiple instances of @c ConfigValues in a
+// single process, as we are using a variant of read-copy-update mechinary to
+// update the settings at runtime.
+class ConfigProxy : public seastar::peering_sharded_service<ConfigProxy>
+{
+  using LocalConfigValues = seastar::lw_shared_ptr<ConfigValues>;
+  seastar::foreign_ptr<LocalConfigValues> values;
+
+  md_config_t* remote_config = nullptr;
+  std::unique_ptr<md_config_t> local_config;
+
+  using ConfigObserver = ceph::md_config_obs_impl<ConfigProxy>;
+  ObserverMgr<ConfigObserver> obs_mgr;
+
+  const md_config_t& get_config() const {
+    return remote_config ? *remote_config : * local_config;
+  }
+  md_config_t& get_config() {
+    return remote_config ? *remote_config : * local_config;
+  }
+
+  // apply changes to all shards
+  // @param func a functor which accepts @c "ConfigValues&"
+  template<typename Func>
+  seastar::future<> do_change(Func&& func) {
+    return container().invoke_on(values.get_owner_shard(),
+                                 [func = std::move(func)](ConfigProxy& owner) {
+      // apply the changes to a copy of the values
+      auto new_values = seastar::make_lw_shared(*owner.values);
+      new_values->changed.clear();
+      func(*new_values);
+
+      // always apply the new settings synchronously on the owner shard, to
+      // avoid racings with other do_change() calls in parallel.
+      ObserverMgr<ConfigObserver>::rev_obs_map rev_obs;
+      owner.values.reset(new_values);
+      owner.obs_mgr.for_each_change(owner.values->changed, owner,
+                                    [&rev_obs](ConfigObserver *obs,
+                                               const std::string &key) {
+                                      rev_obs[obs].insert(key);
+                                    }, nullptr);
+      for (auto& [obs, keys] : rev_obs) {
+        obs->handle_conf_change(owner, keys);
+      }
+
+      return seastar::parallel_for_each(boost::irange(1u, seastar::smp::count),
+                                        [&owner, new_values] (auto cpu) {
+        return owner.container().invoke_on(cpu,
+          [foreign_values = seastar::make_foreign(new_values)](ConfigProxy& proxy) mutable {
+            proxy.values.reset();
+            proxy.values = std::move(foreign_values);
+
+            ObserverMgr<ConfigObserver>::rev_obs_map rev_obs;
+            proxy.obs_mgr.for_each_change(proxy.values->changed, proxy,
+                                          [&rev_obs](md_config_obs_t *obs,
+                                                     const std::string &key) {
+                                            rev_obs[obs].insert(key);
+                                          }, nullptr);
+            for (auto& obs_keys : rev_obs) {
+              obs_keys.first->handle_conf_change(proxy, obs_keys.second);
+            }
+          });
+        }).finally([new_values] {
+          new_values->changed.clear();
+        });
+      });
+  }
+public:
+  ConfigProxy(const EntityName& name, std::string_view cluster);
+  const ConfigValues* operator->() const noexcept {
+    return values.get();
+  }
+  ConfigValues* operator->() noexcept {
+    return values.get();
+  }
+
+  // required by sharded<>
+  seastar::future<> start();
+  seastar::future<> stop() {
+    return seastar::make_ready_future<>();
+  }
+  void add_observer(ConfigObserver* obs) {
+    obs_mgr.add_observer(obs);
+  }
+  void remove_observer(ConfigObserver* obs) {
+    obs_mgr.remove_observer(obs);
+  }
+  seastar::future<> rm_val(const std::string& key) {
+    return do_change([key, this](ConfigValues& values) {
+      auto ret = get_config().rm_val(values, key);
+      if (ret < 0) {
+        throw std::invalid_argument(cpp_strerror(ret));
+      }
+    });
+  }
+  seastar::future<> set_val(const std::string& key,
+			    const std::string& val) {
+    return do_change([key, val, this](ConfigValues& values) {
+      std::stringstream err;
+      auto ret = get_config().set_val(values, obs_mgr, key, val, &err);
+      if (ret < 0) {
+	throw std::invalid_argument(err.str());
+      }
+    });
+  }
+  int get_val(const std::string &key, std::string *val) const {
+    return get_config().get_val(*values, key, val);
+  }
+  template<typename T>
+  const T get_val(const std::string& key) const {
+    return get_config().template get_val<T>(*values, key);
+  }
+
+  int get_all_sections(std::vector<std::string>& sections) const {
+    return get_config().get_all_sections(sections);
+  }
+
+  int get_val_from_conf_file(const std::vector<std::string>& sections,
+			     const std::string& key, std::string& out,
+			     bool expand_meta) const {
+    return get_config().get_val_from_conf_file(*values, sections, key,
+					       out, expand_meta);
+  }
+
+  unsigned get_osd_pool_default_min_size(uint8_t size) const {
+    return get_config().get_osd_pool_default_min_size(*values, size);
+  }
+
+  seastar::future<> set_mon_vals(const std::map<std::string,std::string>& kv) {
+    return do_change([kv, this](ConfigValues& values) {
+      get_config().set_mon_vals(nullptr, values, obs_mgr, kv, nullptr);
+    });
+  }
+
+  seastar::future<> parse_config_files(const std::string& conf_files) {
+    return do_change([this, conf_files](ConfigValues& values) {
+      const char* conf_file_paths =
+	conf_files.empty() ? nullptr : conf_files.c_str();
+      get_config().parse_config_files(values,
+				      obs_mgr,
+				      conf_file_paths,
+				      &std::cerr,
+				      CODE_ENVIRONMENT_DAEMON);
+      });
+  }
+
+  using ShardedConfig = seastar::sharded<ConfigProxy>;
+
+private:
+  static ShardedConfig sharded_conf;
+  friend ConfigProxy& local_conf();
+  friend ShardedConfig& sharded_conf();
+};
+
+inline ConfigProxy& local_conf() {
+  return ConfigProxy::sharded_conf.local();
+}
+
+inline ConfigProxy::ShardedConfig& sharded_conf() {
+  return ConfigProxy::sharded_conf;
+}
+
+}
diff --git a/src/crimson/common/log.cc b/src/crimson/common/log.cc
new file mode 100644
index 00000000..6a57b233
--- /dev/null
+++ b/src/crimson/common/log.cc
@@ -0,0 +1,18 @@
+#include "log.h"
+
+static std::array<seastar::logger, ceph_subsys_get_num()> loggers{
+#define SUBSYS(name, log_level, gather_level) \
+  seastar::logger(#name),
+#define DEFAULT_SUBSYS(log_level, gather_level) \
+  seastar::logger("none"),
+  #include "common/subsys.h"
+#undef SUBSYS
+#undef DEFAULT_SUBSYS
+};
+
+namespace ceph {
+seastar::logger& get_logger(int subsys) {
+  assert(subsys < ceph_subsys_max);
+  return loggers[subsys];
+}
+}
diff --git a/src/crimson/common/log.h b/src/crimson/common/log.h
new file mode 100644
index 00000000..64ff3365
--- /dev/null
+++ b/src/crimson/common/log.h
@@ -0,0 +1,6 @@
+#include <seastar/util/log.hh>
+#include "common/subsys_types.h"
+
+namespace ceph {
+seastar::logger& get_logger(int subsys);
+}
diff --git a/src/crimson/common/perf_counters_collection.cc b/src/crimson/common/perf_counters_collection.cc
new file mode 100644
index 00000000..7a19a9f2
--- /dev/null
+++ b/src/crimson/common/perf_counters_collection.cc
@@ -0,0 +1,22 @@
+#include "perf_counters_collection.h"
+
+namespace ceph::common {
+PerfCountersCollection::PerfCountersCollection()
+{
+  perf_collection = std::make_unique<PerfCountersCollectionImpl>();
+}
+PerfCountersCollection::~PerfCountersCollection()
+{
+  perf_collection->clear();
+}
+
+PerfCountersCollectionImpl* PerfCountersCollection:: get_perf_collection()
+{
+  return perf_collection.get();
+}
+
+PerfCountersCollection::ShardedPerfCountersCollection PerfCountersCollection::sharded_perf_coll;
+
+}
+
+
diff --git a/src/crimson/common/perf_counters_collection.h b/src/crimson/common/perf_counters_collection.h
new file mode 100644
index 00000000..95e2a4f2
--- /dev/null
+++ b/src/crimson/common/perf_counters_collection.h
@@ -0,0 +1,33 @@
+#pragma once
+
+#include "common/perf_counters.h"
+#include <seastar/core/sharded.hh>
+
+namespace ceph::common {
+class PerfCountersCollection: public seastar::sharded<PerfCountersCollection>
+{
+  using ShardedPerfCountersCollection = seastar::sharded<PerfCountersCollection>;
+
+private:
+  std::unique_ptr<PerfCountersCollectionImpl> perf_collection;
+  static ShardedPerfCountersCollection sharded_perf_coll;
+  friend PerfCountersCollection& local_perf_coll();
+  friend ShardedPerfCountersCollection& sharded_perf_coll();
+
+public:
+  PerfCountersCollection();
+  ~PerfCountersCollection();
+  PerfCountersCollectionImpl* get_perf_collection();
+
+};
+
+inline PerfCountersCollection::ShardedPerfCountersCollection& sharded_perf_coll(){
+  return PerfCountersCollection::sharded_perf_coll;
+}
+
+inline PerfCountersCollection& local_perf_coll() {
+  return PerfCountersCollection::sharded_perf_coll.local();
+}
+
+}
+
diff --git a/src/crimson/common/shared_lru.h b/src/crimson/common/shared_lru.h
new file mode 100644
index 00000000..25b1fe5e
--- /dev/null
+++ b/src/crimson/common/shared_lru.h
@@ -0,0 +1,173 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+
+#pragma once
+
+#include <memory>
+#include <optional>
+#include <boost/smart_ptr/local_shared_ptr.hpp>
+#include <boost/smart_ptr/weak_ptr.hpp>
+#include "simple_lru.h"
+
+/// SharedLRU does its best to cache objects. It not only tracks the objects
+/// in its LRU cache with strong references, it also tracks objects with
+/// weak_ptr even if the cache does not hold any strong references to them. so
+/// that it can return the objects after they are evicted, as long as they've
+/// ever been cached and have not been destroyed yet.
+template<class K, class V>
+class SharedLRU {
+  using shared_ptr_t = boost::local_shared_ptr<V>;
+  using weak_ptr_t = boost::weak_ptr<V>;
+  using value_type = std::pair<K, shared_ptr_t>;
+
+  // weak_refs is already ordered, and we don't use accessors like
+  // LRUCache::lower_bound(), so unordered LRUCache would suffice.
+  SimpleLRU<K, shared_ptr_t, false> cache;
+  std::map<K, std::pair<weak_ptr_t, V*>> weak_refs;
+
+  struct Deleter {
+    SharedLRU<K,V>* cache;
+    const K key;
+    void operator()(V* ptr) {
+      cache->_erase(key);
+      delete ptr;
+    }
+  };
+  void _erase(const K& key) {
+    weak_refs.erase(key);
+  }
+public:
+  SharedLRU(size_t max_size = 20)
+    : cache{max_size}
+  {}
+  ~SharedLRU() {
+    cache.clear();
+    // use plain assert() in utiliy classes to avoid dependencies on logging
+    assert(weak_refs.empty());
+  }
+  /**
+   * Returns a reference to the given key, and perform an insertion if such
+   * key does not already exist
+   */
+  shared_ptr_t operator[](const K& key);
+  /**
+   * Returns true iff there are no live references left to anything that has been
+   * in the cache.
+   */
+  bool empty() const {
+    return weak_refs.empty();
+  }
+  size_t size() const {
+    return cache.size();
+  }
+  size_t capacity() const {
+    return cache.capacity();
+  }
+  /***
+   * Inserts a key if not present, or bumps it to the front of the LRU if
+   * it is, and then gives you a reference to the value. If the key already
+   * existed, you are responsible for deleting the new value you tried to
+   * insert.
+   *
+   * @param key The key to insert
+   * @param value The value that goes with the key
+   * @param existed Set to true if the value was already in the
+   * map, false otherwise
+   * @return A reference to the map's value for the given key
+   */
+  shared_ptr_t insert(const K& key, std::unique_ptr<V> value);
+  // clear all strong reference from the lru.
+  void clear() {
+    cache.clear();
+  }
+  shared_ptr_t find(const K& key);
+  // return the last element that is not greater than key
+  shared_ptr_t lower_bound(const K& key);
+  // return the first element that is greater than key
+  std::optional<value_type> upper_bound(const K& key);
+};
+
+template<class K, class V>
+typename SharedLRU<K,V>::shared_ptr_t
+SharedLRU<K,V>::insert(const K& key, std::unique_ptr<V> value)
+{
+  shared_ptr_t val;
+  if (auto found = weak_refs.find(key); found != weak_refs.end()) {
+    val = found->second.first.lock();
+  }
+  if (!val) {
+    val.reset(value.release(), Deleter{this, key});
+    weak_refs.emplace(key, std::make_pair(val, val.get()));
+  }
+  cache.insert(key, val);
+  return val;
+}
+
+template<class K, class V>
+typename SharedLRU<K,V>::shared_ptr_t
+SharedLRU<K,V>::operator[](const K& key)
+{
+  if (auto found = cache.find(key); found) {
+    return *found;
+  }
+  shared_ptr_t val;
+  if (auto found = weak_refs.find(key); found != weak_refs.end()) {
+    val = found->second.first.lock();
+  }
+  if (!val) {
+    val.reset(new V{}, Deleter{this, key});
+    weak_refs.emplace(key, std::make_pair(val, val.get()));
+  }
+  cache.insert(key, val);
+  return val;
+}
+
+template<class K, class V>
+typename SharedLRU<K,V>::shared_ptr_t
+SharedLRU<K,V>::find(const K& key)
+{
+  if (auto found = cache.find(key); found) {
+    return *found;
+  }
+  shared_ptr_t val;
+  if (auto found = weak_refs.find(key); found != weak_refs.end()) {
+    val = found->second.first.lock();
+  }
+  if (val) {
+    cache.insert(key, val);
+  }
+  return val;
+}
+
+template<class K, class V>
+typename SharedLRU<K,V>::shared_ptr_t
+SharedLRU<K,V>::lower_bound(const K& key)
+{
+  if (weak_refs.empty()) {
+    return {};
+  }
+  auto found = weak_refs.lower_bound(key);
+  if (found == weak_refs.end()) {
+    --found;
+  }
+  if (auto val = found->second.first.lock(); val) {
+    cache.insert(key, val);
+    return val;
+  } else {
+    return {};
+  }
+}
+
+template<class K, class V>
+std::optional<typename SharedLRU<K,V>::value_type>
+SharedLRU<K,V>::upper_bound(const K& key)
+{
+  for (auto found = weak_refs.upper_bound(key);
+       found != weak_refs.end();
+       ++found) {
+    if (auto val = found->second.first.lock(); val) {
+      return std::make_pair(found->first, val);
+    }
+  }
+  return std::nullopt;
+}
diff --git a/src/crimson/common/simple_lru.h b/src/crimson/common/simple_lru.h
new file mode 100644
index 00000000..fca1061f
--- /dev/null
+++ b/src/crimson/common/simple_lru.h
@@ -0,0 +1,141 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+
+#pragma once
+
+#include <list>
+#include <map>
+#include <optional>
+#include <type_traits>
+#include <unordered_map>
+
+template <class Key, class Value, bool Ordered>
+class SimpleLRU {
+  static_assert(std::is_default_constructible_v<Value>);
+  using list_type = std::list<Key>;
+  template<class K, class V>
+  using map_t = std::conditional_t<Ordered,
+				   std::map<K, V>,
+				   std::unordered_map<K, V>>;
+  using map_type = map_t<Key, std::pair<Value, typename list_type::iterator>>;
+  list_type lru;
+  map_type cache;
+  const size_t max_size;
+
+public:
+  SimpleLRU(size_t size = 20)
+    : cache(size),
+      max_size(size)
+  {}
+  size_t size() const {
+    return cache.size();
+  }
+  size_t capacity() const {
+    return max_size;
+  }
+  using insert_return_type = std::pair<Value, bool>;
+  insert_return_type insert(const Key& key, Value value);
+  std::optional<Value> find(const Key& key);
+  std::optional<std::enable_if<Ordered, Value>> lower_bound(const Key& key);
+  void erase(const Key& key);
+  void clear();
+private:
+  // bump the item to the front of the lru list
+  Value _lru_add(typename map_type::iterator found);
+  // evict the last element of most recently used list
+  void _evict();
+};
+
+template <class Key, class Value, bool Ordered>
+typename SimpleLRU<Key,Value,Ordered>::insert_return_type
+SimpleLRU<Key,Value,Ordered>::insert(const Key& key, Value value)
+{
+  if constexpr(Ordered) {
+    auto found = cache.lower_bound(key);
+    if (found != cache.end() && found->first == key) {
+      // already exists
+      return {found->second.first, true};
+    } else {
+      if (size() >= capacity()) {
+        _evict();
+      }
+      lru.push_front(key);
+      // use lower_bound as hint to save the lookup
+      cache.emplace_hint(found, key, std::make_pair(value, lru.begin()));
+      return {std::move(value), false};
+    }
+  } else {
+    // cache is not ordered
+    auto found = cache.find(key);
+    if (found != cache.end()) {
+      // already exists
+      return {found->second.first, true};
+    } else {
+      if (size() >= capacity()) {
+	_evict();
+      }
+      lru.push_front(key);
+      cache.emplace(key, std::make_pair(value, lru.begin()));
+      return {std::move(value), false};
+    }
+  }
+}
+
+template <class Key, class Value, bool Ordered>
+std::optional<Value> SimpleLRU<Key,Value,Ordered>::find(const Key& key)
+{
+  if (auto found = cache.find(key); found != cache.end()){
+    return _lru_add(found);
+  } else {
+    return {};
+  }
+}
+
+template <class Key, class Value, bool Ordered>
+std::optional<std::enable_if<Ordered, Value>>
+SimpleLRU<Key,Value,Ordered>::lower_bound(const Key& key)
+{
+  if (auto found = cache.lower_bound(key); found != cache.end()) {
+    return _lru_add(found);
+  } else {
+    return {};
+  }
+}
+
+template <class Key, class Value, bool Ordered>
+void SimpleLRU<Key,Value,Ordered>::clear()
+{
+  lru.clear();
+  cache.clear();
+}
+
+template <class Key, class Value, bool Ordered>
+void SimpleLRU<Key,Value,Ordered>::erase(const Key& key)
+{
+  if (auto found = cache.find(key); found != cache.end()) {
+    lru.erase(found->second->second);
+    cache.erase(found);
+  }
+}
+
+template <class Key, class Value, bool Ordered>
+Value SimpleLRU<Key,Value,Ordered>::_lru_add(
+  typename SimpleLRU<Key,Value,Ordered>::map_type::iterator found)
+{
+  auto& [value, in_lru] = found->second;
+  if (in_lru != lru.begin()){
+    // move item to the front
+    lru.splice(lru.begin(), lru, in_lru);
+  }
+  // the item is already at the front
+  return value;
+}
+
+template <class Key, class Value, bool Ordered>
+void SimpleLRU<Key,Value,Ordered>::_evict()
+{
+  // evict the last element of most recently used list
+  auto last = --lru.end();
+  cache.erase(*last);
+  lru.erase(last);
+}
diff --git a/src/crimson/mon/MonClient.cc b/src/crimson/mon/MonClient.cc
new file mode 100644
index 00000000..4b61270c
--- /dev/null
+++ b/src/crimson/mon/MonClient.cc
@@ -0,0 +1,606 @@
+#include "MonClient.h"
+
+#include <random>
+
+#include <seastar/core/future-util.hh>
+#include <seastar/core/lowres_clock.hh>
+#include <seastar/util/log.hh>
+
+#include "auth/AuthClientHandler.h"
+#include "auth/AuthMethodList.h"
+#include "auth/RotatingKeyRing.h"
+
+#include "common/hostname.h"
+
+#include "crimson/auth/KeyRing.h"
+#include "crimson/common/config_proxy.h"
+#include "crimson/common/log.h"
+#include "crimson/net/Connection.h"
+#include "crimson/net/Errors.h"
+#include "crimson/net/Messenger.h"
+
+#include "messages/MAuth.h"
+#include "messages/MAuthReply.h"
+#include "messages/MConfig.h"
+#include "messages/MLogAck.h"
+#include "messages/MMonCommand.h"
+#include "messages/MMonCommandAck.h"
+#include "messages/MMonGetVersion.h"
+#include "messages/MMonGetVersionReply.h"
+#include "messages/MMonMap.h"
+#include "messages/MMonSubscribe.h"
+#include "messages/MMonSubscribeAck.h"
+
+namespace {
+  seastar::logger& logger()
+  {
+    return ceph::get_logger(ceph_subsys_monc);
+  }
+
+  template<typename Message, typename... Args>
+  Ref<Message> make_message(Args&&... args)
+  {
+    return {new Message{std::forward<Args>(args)...}, false};
+  }
+}
+
+namespace ceph::mon {
+
+
+class Connection {
+public:
+  Connection(ceph::net::ConnectionRef conn,
+	     KeyRing* keyring);
+  seastar::future<> handle_auth_reply(Ref<MAuthReply> m);
+  seastar::future<> authenticate(epoch_t epoch,
+				 const EntityName& name,
+				 const AuthMethodList& auth_methods,
+				 uint32_t want_keys);
+  seastar::future<> close();
+  bool is_my_peer(const entity_addr_t& addr) const;
+
+  seastar::future<> renew_tickets();
+  ceph::net::ConnectionRef get_conn();
+
+private:
+  seastar::future<> setup_session(epoch_t epoch,
+				  const AuthMethodList& auth_methods,
+				  const EntityName& name);
+  std::unique_ptr<AuthClientHandler> create_auth(Ref<MAuthReply> m,
+						 const EntityName& name,
+						 uint32_t want_keys);
+  seastar::future<bool> do_auth();
+
+private:
+  bool closed = false;
+  seastar::promise<Ref<MAuthReply>> reply;
+  ceph::net::ConnectionRef conn;
+  std::unique_ptr<AuthClientHandler> auth;
+  RotatingKeyRing rotating_keyring;
+  uint64_t global_id;
+};
+
+Connection::Connection(ceph::net::ConnectionRef conn,
+                       KeyRing* keyring)
+  : conn{conn},
+    rotating_keyring{nullptr, CEPH_ENTITY_TYPE_OSD, keyring}
+{}
+
+seastar::future<> Connection::handle_auth_reply(Ref<MAuthReply> m)
+{
+  reply.set_value(m);
+  return seastar::now();
+}
+
+seastar::future<> Connection::renew_tickets()
+{
+  if (auth->need_tickets()) {
+    return do_auth().then([](bool success) {
+      if (!success)  {
+        throw std::system_error(make_error_code(
+          ceph::net::error::negotiation_failure));
+      }
+    });
+  }
+  return seastar::now();
+}
+
+std::unique_ptr<AuthClientHandler>
+Connection::create_auth(Ref<MAuthReply> m,
+                        const EntityName& name,
+                        uint32_t want_keys)
+{
+  static CephContext cct;
+  std::unique_ptr<AuthClientHandler> auth;
+  auth.reset(AuthClientHandler::create(&cct,
+                                       m->protocol,
+                                       &rotating_keyring));
+  if (!auth) {
+    logger().error("no handler for protocol {}", m->protocol);
+    throw std::system_error(make_error_code(
+      ceph::net::error::negotiation_failure));
+  }
+  auth->init(name);
+  auth->set_want_keys(want_keys);
+  auth->set_global_id(global_id);
+
+  if (m->global_id != global_id) {
+    // it's a new session
+    auth->set_global_id(global_id);
+    auth->reset();
+  }
+  return auth;
+}
+
+seastar::future<>
+Connection::setup_session(epoch_t epoch,
+                          const AuthMethodList& auth_methods,
+                          const EntityName& name)
+{
+  auto m = make_message<MAuth>();
+  m->protocol = 0;
+  m->monmap_epoch = epoch;
+  __u8 struct_v = 1;
+  encode(struct_v, m->auth_payload);
+  encode(auth_methods.get_supported_set(), m->auth_payload);
+  encode(name, m->auth_payload);
+  encode(global_id, m->auth_payload);
+  return conn->send(m);
+}
+
+seastar::future<bool> Connection::do_auth()
+{
+  auto m = make_message<MAuth>();
+  m->protocol = auth->get_protocol();
+  auth->prepare_build_request();
+  if (int ret = auth->build_request(m->auth_payload); ret) {
+    logger().error("missing/bad key for '{}'",
+                   ceph::common::local_conf()->name);
+    throw std::system_error(make_error_code(
+      ceph::net::error::negotiation_failure));
+  }
+  logger().info("sending {}", *m);
+  return conn->send(m).then([this] {
+    logger().info("waiting");
+    return reply.get_future();
+  }).then([this] (Ref<MAuthReply> m) {
+    logger().info("mon {} => {} returns {}: {}",
+                   conn->get_messenger()->get_myaddr(),
+                   conn->get_peer_addr(), *m, m->result);
+    reply = decltype(reply){};
+    auto p = m->result_bl.cbegin();
+    auto ret = auth->handle_response(m->result, p,
+#warning fix crimson: session_key, connection_secret
+				     nullptr, nullptr);
+    if (ret != 0 && ret != -EAGAIN) {
+      throw std::system_error(make_error_code(
+        ceph::net::error::negotiation_failure));
+    }
+    return seastar::make_ready_future<bool>(ret == 0);
+  });
+}
+
+seastar::future<>
+Connection::authenticate(epoch_t epoch,
+                         const EntityName& name,
+                         const AuthMethodList& auth_methods,
+                         uint32_t want_keys)
+{
+  return conn->keepalive().then([epoch, auth_methods, name, this] {
+    return setup_session(epoch, auth_methods, name);
+  }).then([this] {
+    return reply.get_future();
+  }).then([name, want_keys, this](Ref<MAuthReply> m) {
+    reply = decltype(reply){};
+    auth = create_auth(m, name, want_keys);
+    global_id = m->global_id;
+    switch (auto p = m->result_bl.cbegin();
+            auth->handle_response(m->result, p,
+#warning fix crimson: session_key, connection_secret
+				  nullptr, nullptr)) {
+    case 0:
+      // none
+      return seastar::now();
+    case -EAGAIN:
+      // cephx
+      return seastar::repeat([this] {
+        return do_auth().then([](bool success) {
+          return seastar::make_ready_future<seastar::stop_iteration>(
+            success ?
+            seastar::stop_iteration::yes:
+            seastar::stop_iteration::no);
+          });
+        });
+    default:
+      ceph_assert_always(0);
+    }
+  });
+}
+
+seastar::future<> Connection::close()
+{
+  if (conn && !std::exchange(closed, true)) {
+    return conn->close();
+  } else {
+    return seastar::now();
+  }
+}
+
+bool Connection::is_my_peer(const entity_addr_t& addr) const
+{
+  return conn->get_peer_addr() == addr;
+}
+
+ceph::net::ConnectionRef Connection::get_conn() {
+  return conn;
+}
+
+namespace {
+auto create_auth_methods(uint32_t entity_type)
+{
+  auto& conf = ceph::common::local_conf();
+  std::string method;
+  const auto auth_supported = conf.get_val<std::string>("auth_supported");
+  if (!auth_supported.empty()) {
+    method = auth_supported;
+  } else if (entity_type & (CEPH_ENTITY_TYPE_OSD |
+                            CEPH_ENTITY_TYPE_MDS |
+                            CEPH_ENTITY_TYPE_MON |
+                            CEPH_ENTITY_TYPE_MGR)) {
+    method = conf.get_val<std::string>("auth_cluster_required");
+  } else {
+    method = conf.get_val<std::string>("auth_client_required");
+  }
+  return std::make_unique<AuthMethodList>(nullptr, method);
+}
+}
+
+Client::Client(ceph::net::Messenger& messenger)
+  // currently, crimson is OSD-only
+  : want_keys{CEPH_ENTITY_TYPE_MON |
+              CEPH_ENTITY_TYPE_OSD |
+              CEPH_ENTITY_TYPE_MGR},
+    timer{[this] { tick(); }},
+    msgr{messenger}
+{}
+
+Client::Client(Client&&) = default;
+Client::~Client() = default;
+
+seastar::future<> Client::start() {
+  entity_name = ceph::common::local_conf()->name;
+  // should always be OSD, though
+  auth_methods = create_auth_methods(entity_name.get_type());
+  return load_keyring().then([this] {
+    return monmap.build_initial(ceph::common::local_conf(), false);
+  }).then([this] {
+    return authenticate();
+  });
+}
+
+seastar::future<> Client::load_keyring()
+{
+  if (!auth_methods->is_supported_auth(CEPH_AUTH_CEPHX)) {
+    return seastar::now();
+  } else {
+    return ceph::auth::load_from_keyring(&keyring).then([](KeyRing* keyring) {
+      return ceph::auth::load_from_keyfile(keyring);
+    }).then([](KeyRing* keyring) {
+      return ceph::auth::load_from_key(keyring);
+    }).then([](KeyRing*) {
+      return seastar::now();
+    });
+  }
+}
+
+void Client::tick()
+{
+  seastar::with_gate(tick_gate, [this] {
+    return active_con->renew_tickets();
+  });
+}
+
+bool Client::is_hunting() const {
+  return !active_con;
+}
+
+seastar::future<>
+Client::ms_dispatch(ceph::net::ConnectionRef conn, MessageRef m)
+{
+  logger().info("ms_dispatch {}", *m);
+  // we only care about these message types
+  switch (m->get_type()) {
+  case CEPH_MSG_MON_MAP:
+    return handle_monmap(conn, boost::static_pointer_cast<MMonMap>(m));
+  case CEPH_MSG_AUTH_REPLY:
+    return handle_auth_reply(
+      conn, boost::static_pointer_cast<MAuthReply>(m));
+  case CEPH_MSG_MON_SUBSCRIBE_ACK:
+    return handle_subscribe_ack(
+      boost::static_pointer_cast<MMonSubscribeAck>(m));
+  case CEPH_MSG_MON_GET_VERSION_REPLY:
+    return handle_get_version_reply(
+      boost::static_pointer_cast<MMonGetVersionReply>(m));
+  case MSG_MON_COMMAND_ACK:
+    return handle_mon_command_ack(
+      boost::static_pointer_cast<MMonCommandAck>(m));
+  case MSG_LOGACK:
+    return handle_log_ack(
+      boost::static_pointer_cast<MLogAck>(m));
+  case MSG_CONFIG:
+    return handle_config(
+      boost::static_pointer_cast<MConfig>(m));
+  default:
+    return seastar::now();
+  }
+}
+
+seastar::future<> Client::ms_handle_reset(ceph::net::ConnectionRef conn)
+{
+  auto found = std::find_if(pending_conns.begin(), pending_conns.end(),
+                            [peer_addr = conn->get_peer_addr()](auto& mc) {
+                              return mc.is_my_peer(peer_addr);
+                            });
+  if (found != pending_conns.end()) {
+    logger().warn("pending conn reset by {}", conn->get_peer_addr());
+    return found->close();
+  } else if (active_con && active_con->is_my_peer(conn->get_peer_addr())) {
+    logger().warn("active conn reset {}", conn->get_peer_addr());
+    active_con.reset();
+    return reopen_session(-1);
+  } else {
+    logger().error("unknown reset from {}", conn->get_peer_addr());
+    return seastar::now();
+  }
+}
+
+seastar::future<> Client::handle_monmap(ceph::net::ConnectionRef conn,
+                                        Ref<MMonMap> m)
+{
+  monmap.decode(m->monmapbl);
+  const auto peer_addr = conn->get_peer_addr();
+  auto cur_mon = monmap.get_name(peer_addr);
+  logger().info("got monmap {}, mon.{}, is now rank {}",
+                 monmap.epoch, cur_mon, monmap.get_rank(cur_mon));
+  sub.got("monmap", monmap.get_epoch());
+
+  if (monmap.get_addr_name(peer_addr, cur_mon)) {
+    return seastar::now();
+  } else {
+    logger().warn("mon.{} went away", cur_mon);
+    return reopen_session(-1);
+  }
+}
+
+seastar::future<> Client::handle_auth_reply(ceph::net::ConnectionRef conn,
+                                               Ref<MAuthReply> m)
+{
+  logger().info("mon {} => {} returns {}: {}",
+                conn->get_messenger()->get_myaddr(),
+                conn->get_peer_addr(), *m, m->result);
+  auto found = std::find_if(pending_conns.begin(), pending_conns.end(),
+                            [peer_addr = conn->get_peer_addr()](auto& mc) {
+                              return mc.is_my_peer(peer_addr);
+                            });
+  if (found != pending_conns.end()) {
+    return found->handle_auth_reply(m);
+  } else if (active_con) {
+    return active_con->handle_auth_reply(m);
+  } else {
+    logger().error("unknown auth reply from {}", conn->get_peer_addr());
+    return seastar::now();
+  }
+}
+
+seastar::future<> Client::handle_subscribe_ack(Ref<MMonSubscribeAck> m)
+{
+  sub.acked(m->interval);
+  return seastar::now();
+}
+
+Client::get_version_t Client::get_version(const std::string& map)
+{
+  auto m = make_message<MMonGetVersion>();
+  auto tid = ++last_version_req_id;
+  m->handle = tid;
+  m->what = map;
+  auto& req = version_reqs[tid];
+  return active_con->get_conn()->send(m).then([&req] {
+    return req.get_future();
+  });
+}
+
+seastar::future<>
+Client::handle_get_version_reply(Ref<MMonGetVersionReply> m)
+{
+  if (auto found = version_reqs.find(m->handle);
+      found != version_reqs.end()) {
+    auto& result = found->second;
+    logger().trace("{}: {} returns {}",
+                 __func__, m->handle, m->version);
+    result.set_value(m->version, m->oldest_version);
+    version_reqs.erase(found);
+  } else {
+    logger().warn("{}: version request with handle {} not found",
+                __func__, m->handle);
+  }
+  return seastar::now();
+}
+
+seastar::future<> Client::handle_mon_command_ack(Ref<MMonCommandAck> m)
+{
+  const auto tid = m->get_tid();
+  if (auto found = mon_commands.find(tid);
+      found != mon_commands.end()) {
+    auto& result = found->second;
+    logger().trace("{} {}", __func__, tid);
+    result.set_value(m->r, m->rs, std::move(m->get_data()));
+    mon_commands.erase(found);
+  } else {
+    logger().warn("{} {} not found", __func__, tid);
+  }
+  return seastar::now();
+}
+
+seastar::future<> Client::handle_log_ack(Ref<MLogAck> m)
+{
+  // XXX
+  return seastar::now();
+}
+
+seastar::future<> Client::handle_config(Ref<MConfig> m)
+{
+  return ceph::common::local_conf().set_mon_vals(m->config);
+}
+
+std::vector<unsigned> Client::get_random_mons(unsigned n) const
+{
+  uint16_t min_priority = std::numeric_limits<uint16_t>::max();
+  for (const auto& m : monmap.mon_info) {
+    if (m.second.priority < min_priority) {
+      min_priority = m.second.priority;
+    }
+  }
+  vector<unsigned> ranks;
+  for (auto [name, info] : monmap.mon_info) {
+    // TODO: #msgr-v2
+    if (info.public_addrs.legacy_addr().is_blank_ip()) {
+      continue;
+    }
+    if (info.priority == min_priority) {
+      ranks.push_back(monmap.get_rank(name));
+    }
+  }
+  std::random_device rd;
+  std::default_random_engine rng{rd()};
+  std::shuffle(ranks.begin(), ranks.end(), rng);
+  if (n == 0 || n > ranks.size()) {
+    return ranks;
+  } else {
+    return {ranks.begin(), ranks.begin() + n};
+  }
+}
+
+seastar::future<> Client::authenticate()
+{
+  return reopen_session(-1);
+}
+
+seastar::future<> Client::stop()
+{
+  return tick_gate.close().then([this] {
+    if (active_con) {
+      return active_con->close();
+    } else {
+      return seastar::now();
+    }
+  });
+}
+
+seastar::future<> Client::reopen_session(int rank)
+{
+  vector<unsigned> mons;
+  if (rank >= 0) {
+    mons.push_back(rank);
+  } else {
+    const auto parallel =
+      ceph::common::local_conf().get_val<uint64_t>("mon_client_hunt_parallel");
+    mons = get_random_mons(parallel);
+  }
+  pending_conns.reserve(mons.size());
+  return seastar::parallel_for_each(mons, [this](auto rank) {
+#warning fixme
+    auto peer = monmap.get_addrs(rank).legacy_addr();
+    logger().info("connecting to mon.{}", rank);
+    return msgr.connect(peer, CEPH_ENTITY_TYPE_MON)
+    .then([this] (auto xconn) {
+      // sharded-messenger compatible mode assumes all connections running
+      // in one shard.
+      ceph_assert((*xconn)->shard_id() == seastar::engine().cpu_id());
+      ceph::net::ConnectionRef conn = xconn->release();
+      auto& mc = pending_conns.emplace_back(conn, &keyring);
+      return mc.authenticate(
+        monmap.get_epoch(), entity_name,
+        *auth_methods, want_keys).handle_exception([conn](auto ep) {
+        return conn->close().then([ep = std::move(ep)] {
+          std::rethrow_exception(ep);
+        });
+      });
+    }).then([peer, this] {
+      if (!is_hunting()) {
+        return seastar::now();
+      }
+      auto found = std::find_if(pending_conns.begin(), pending_conns.end(),
+                                [peer](auto& mc) {
+                                  return mc.is_my_peer(peer);
+                                });
+      ceph_assert_always(found != pending_conns.end());
+      active_con.reset(new Connection{std::move(*found)});
+      return seastar::parallel_for_each(pending_conns, [] (auto& conn) {
+        return conn.close();
+      });
+    });
+  }).then([this] {
+    pending_conns.clear();
+  });
+}
+
+Client::command_result_t
+Client::run_command(const std::vector<std::string>& cmd,
+                    const bufferlist& bl)
+{
+  auto m = make_message<MMonCommand>(monmap.fsid);
+  auto tid = ++last_mon_command_id;
+  m->set_tid(tid);
+  m->cmd = cmd;
+  m->set_data(bl);
+  auto& req = mon_commands[tid];
+  return active_con->get_conn()->send(m).then([&req] {
+    return req.get_future();
+  });
+}
+
+seastar::future<> Client::send_message(MessageRef m)
+{
+  return active_con->get_conn()->send(m);
+}
+
+bool Client::sub_want(const std::string& what, version_t start, unsigned flags)
+{
+  return sub.want(what, start, flags);
+}
+
+void Client::sub_got(const std::string& what, version_t have)
+{
+  sub.got(what, have);
+}
+
+void Client::sub_unwant(const std::string& what)
+{
+  sub.unwant(what);
+}
+
+bool Client::sub_want_increment(const std::string& what,
+                                version_t start,
+                                unsigned flags)
+{
+  return sub.inc_want(what, start, flags);
+}
+
+seastar::future<> Client::renew_subs()
+{
+  if (!sub.have_new()) {
+    logger().warn("{} - empty", __func__);
+    return seastar::now();
+  }
+  logger().trace("{}", __func__);
+
+  auto m = make_message<MMonSubscribe>();
+  m->what = sub.get_subs();
+  m->hostname = ceph_get_short_hostname();
+  return active_con->get_conn()->send(m).then([this] {
+    sub.renewed();
+  });
+}
+
+} // namespace ceph::mon
diff --git a/src/crimson/mon/MonClient.h b/src/crimson/mon/MonClient.h
new file mode 100644
index 00000000..ef9bcb69
--- /dev/null
+++ b/src/crimson/mon/MonClient.h
@@ -0,0 +1,114 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+
+#pragma once
+
+#include <memory>
+
+#include <seastar/core/future.hh>
+#include <seastar/core/gate.hh>
+#include <seastar/core/lowres_clock.hh>
+#include <seastar/core/timer.hh>
+
+#include "auth/KeyRing.h"
+
+#include "crimson/net/Dispatcher.h"
+#include "crimson/net/Fwd.h"
+
+#include "mon/MonMap.h"
+
+#include "mon/MonSub.h"
+
+template<typename Message> using Ref = boost::intrusive_ptr<Message>;
+namespace ceph::net {
+  class Messenger;
+}
+
+class AuthMethodList;
+class MAuthReply;
+struct MMonMap;
+struct MMonSubscribeAck;
+struct MMonGetVersionReply;
+struct MMonCommandAck;
+struct MLogAck;
+struct MConfig;
+
+namespace ceph::mon {
+
+class Connection;
+
+class Client : public ceph::net::Dispatcher {
+  EntityName entity_name;
+  KeyRing keyring;
+  std::unique_ptr<AuthMethodList> auth_methods;
+  const uint32_t want_keys;
+
+  MonMap monmap;
+  seastar::promise<MessageRef> reply;
+  std::unique_ptr<Connection> active_con;
+  std::vector<Connection> pending_conns;
+  seastar::timer<seastar::lowres_clock> timer;
+  seastar::gate tick_gate;
+
+  ceph::net::Messenger& msgr;
+
+  // commands
+  using get_version_t = seastar::future<version_t, version_t>;
+
+  ceph_tid_t last_version_req_id = 0;
+  std::map<ceph_tid_t, typename get_version_t::promise_type> version_reqs;
+
+  ceph_tid_t last_mon_command_id = 0;
+  using command_result_t =
+    seastar::future<std::int32_t, string, ceph::bufferlist>;
+  std::map<ceph_tid_t, typename command_result_t::promise_type> mon_commands;
+
+  MonSub sub;
+
+public:
+  Client(ceph::net::Messenger& messenger);
+  Client(Client&&);
+  ~Client();
+  seastar::future<> start();
+  seastar::future<> stop();
+
+  const uuid_d& get_fsid() const {
+    return monmap.fsid;
+  }
+  get_version_t get_version(const std::string& map);
+  command_result_t run_command(const std::vector<std::string>& cmd,
+			       const bufferlist& bl);
+  seastar::future<> send_message(MessageRef);
+  bool sub_want(const std::string& what, version_t start, unsigned flags);
+  void sub_got(const std::string& what, version_t have);
+  void sub_unwant(const std::string& what);
+  bool sub_want_increment(const std::string& what, version_t start, unsigned flags);
+  seastar::future<> renew_subs();
+
+private:
+  void tick();
+
+  seastar::future<> ms_dispatch(ceph::net::ConnectionRef conn,
+				MessageRef m) override;
+  seastar::future<> ms_handle_reset(ceph::net::ConnectionRef conn) override;
+
+  seastar::future<> handle_monmap(ceph::net::ConnectionRef conn,
+				  Ref<MMonMap> m);
+  seastar::future<> handle_auth_reply(ceph::net::ConnectionRef conn,
+				      Ref<MAuthReply> m);
+  seastar::future<> handle_subscribe_ack(Ref<MMonSubscribeAck> m);
+  seastar::future<> handle_get_version_reply(Ref<MMonGetVersionReply> m);
+  seastar::future<> handle_mon_command_ack(Ref<MMonCommandAck> m);
+  seastar::future<> handle_log_ack(Ref<MLogAck> m);
+  seastar::future<> handle_config(Ref<MConfig> m);
+
+private:
+  seastar::future<> load_keyring();
+  seastar::future<> authenticate();
+
+  bool is_hunting() const;
+  seastar::future<> reopen_session(int rank);
+  std::vector<unsigned> get_random_mons(unsigned n) const;
+  seastar::future<> _add_conn(unsigned rank, uint64_t global_id);
+};
+
+} // namespace ceph::mon
diff --git a/src/crimson/net/Config.h b/src/crimson/net/Config.h
new file mode 100644
index 00000000..90929bde
--- /dev/null
+++ b/src/crimson/net/Config.h
@@ -0,0 +1,26 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+
+// XXX: a poor man's md_config_t
+#pragma once
+
+#include "include/msgr.h"
+#include <chrono>
+
+namespace ceph::net {
+
+using namespace std::literals::chrono_literals;
+
+constexpr struct simple_md_config_t {
+  uint32_t host_type = CEPH_ENTITY_TYPE_OSD;
+  bool cephx_require_signatures = false;
+  bool cephx_cluster_require_signatures = false;
+  bool cephx_service_require_signatures = false;
+  bool ms_die_on_old_message = true;
+  bool ms_die_on_skipped_message = true;
+  std::chrono::milliseconds ms_initial_backoff = 200ms;
+  std::chrono::milliseconds ms_max_backoff = 15000ms;
+  std::chrono::milliseconds threadpool_empty_queue_max_wait = 100ms;
+  size_t osd_client_message_size_cap = 500ULL << 20;
+} conf;
+}
diff --git a/src/crimson/net/Connection.h b/src/crimson/net/Connection.h
new file mode 100644
index 00000000..b1b72c74
--- /dev/null
+++ b/src/crimson/net/Connection.h
@@ -0,0 +1,66 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+/*
+ * Ceph - scalable distributed file system
+ *
+ * Copyright (C) 2017 Red Hat, Inc
+ *
+ * This is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License version 2.1, as published by the Free Software
+ * Foundation.  See file COPYING.
+ *
+ */
+
+#pragma once
+
+#include <queue>
+#include <seastar/core/future.hh>
+#include <seastar/core/shared_ptr.hh>
+
+#include "Fwd.h"
+
+namespace ceph::net {
+
+using seq_num_t = uint64_t;
+
+class Connection : public seastar::enable_shared_from_this<Connection> {
+ protected:
+  entity_addr_t peer_addr;
+  peer_type_t peer_type = -1;
+
+ public:
+  Connection() {}
+  virtual ~Connection() {}
+
+  virtual Messenger* get_messenger() const = 0;
+  const entity_addr_t& get_peer_addr() const { return peer_addr; }
+  virtual int get_peer_type() const = 0;
+
+  /// true if the handshake has completed and no errors have been encountered
+  virtual seastar::future<bool> is_connected() = 0;
+
+  /// send a message over a connection that has completed its handshake
+  virtual seastar::future<> send(MessageRef msg) = 0;
+
+  /// send a keepalive message over a connection that has completed its
+  /// handshake
+  virtual seastar::future<> keepalive() = 0;
+
+  /// close the connection and cancel any any pending futures from read/send
+  virtual seastar::future<> close() = 0;
+
+  /// which shard id the connection lives
+  virtual seastar::shard_id shard_id() const = 0;
+
+  virtual void print(ostream& out) const = 0;
+};
+
+inline ostream& operator<<(ostream& out, const Connection& conn) {
+  out << "[";
+  conn.print(out);
+  out << "]";
+  return out;
+}
+
+} // namespace ceph::net
diff --git a/src/crimson/net/Dispatcher.cc b/src/crimson/net/Dispatcher.cc
new file mode 100644
index 00000000..336ded38
--- /dev/null
+++ b/src/crimson/net/Dispatcher.cc
@@ -0,0 +1,11 @@
+#include "auth/Auth.h"
+#include "Dispatcher.h"
+
+namespace ceph::net
+{
+seastar::future<std::unique_ptr<AuthAuthorizer>>
+Dispatcher::ms_get_authorizer(peer_type_t)
+{
+  return seastar::make_ready_future<std::unique_ptr<AuthAuthorizer>>(nullptr);
+}
+}
diff --git a/src/crimson/net/Dispatcher.h b/src/crimson/net/Dispatcher.h
new file mode 100644
index 00000000..cbde1549
--- /dev/null
+++ b/src/crimson/net/Dispatcher.h
@@ -0,0 +1,65 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+/*
+ * Ceph - scalable distributed file system
+ *
+ * Copyright (C) 2017 Red Hat, Inc
+ *
+ * This is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License version 2.1, as published by the Free Software
+ * Foundation.  See file COPYING.
+ *
+ */
+
+#pragma once
+
+#include <seastar/core/future.hh>
+#include <seastar/core/sharded.hh>
+
+#include "Fwd.h"
+
+class AuthAuthorizer;
+
+namespace ceph::net {
+
+class Dispatcher {
+ public:
+  virtual ~Dispatcher() {}
+
+  virtual seastar::future<> ms_dispatch(ConnectionRef conn, MessageRef m) {
+    return seastar::make_ready_future<>();
+  }
+
+  virtual seastar::future<> ms_handle_accept(ConnectionRef conn) {
+    return seastar::make_ready_future<>();
+  }
+
+  virtual seastar::future<> ms_handle_connect(ConnectionRef conn) {
+    return seastar::make_ready_future<>();
+  }
+
+  virtual seastar::future<> ms_handle_reset(ConnectionRef conn) {
+    return seastar::make_ready_future<>();
+  }
+
+  virtual seastar::future<> ms_handle_remote_reset(ConnectionRef conn) {
+    return seastar::make_ready_future<>();
+  }
+
+  virtual seastar::future<msgr_tag_t, bufferlist>
+  ms_verify_authorizer(peer_type_t,
+		       auth_proto_t,
+		       bufferlist&) {
+    return seastar::make_ready_future<msgr_tag_t, bufferlist>(0, bufferlist{});
+  }
+  virtual seastar::future<std::unique_ptr<AuthAuthorizer>>
+  ms_get_authorizer(peer_type_t);
+
+  // get the local dispatcher shard if it is accessed by another core
+  virtual Dispatcher* get_local_shard() {
+    return this;
+  }
+};
+
+} // namespace ceph::net
diff --git a/src/crimson/net/Errors.cc b/src/crimson/net/Errors.cc
new file mode 100644
index 00000000..62d60ce1
--- /dev/null
+++ b/src/crimson/net/Errors.cc
@@ -0,0 +1,107 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+/*
+ * Ceph - scalable distributed file system
+ *
+ * Copyright (C) 2017 Red Hat, Inc
+ *
+ * This is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License version 2.1, as published by the Free Software
+ * Foundation.  See file COPYING.
+ *
+ */
+
+#include "Errors.h"
+
+namespace ceph::net {
+
+const std::error_category& net_category()
+{
+  struct category : public std::error_category {
+    const char* name() const noexcept override {
+      return "ceph::net";
+    }
+
+    std::string message(int ev) const override {
+      switch (static_cast<error>(ev)) {
+        case error::success:
+          return "success";
+        case error::bad_connect_banner:
+          return "bad connect banner";
+        case error::bad_peer_address:
+          return "bad peer address";
+        case error::negotiation_failure:
+          return "negotiation failure";
+        case error::read_eof:
+          return "read eof";
+        case error::connection_aborted:
+          return "connection aborted";
+        case error::connection_refused:
+          return "connection refused";
+        case error::connection_reset:
+          return "connection reset";
+        default:
+          return "unknown";
+      }
+    }
+
+    // unfortunately, seastar throws connection errors with the system category,
+    // rather than the generic category that would match their counterparts
+    // in std::errc. we add our own errors for them, so we can match either
+    std::error_condition default_error_condition(int ev) const noexcept override {
+      switch (static_cast<error>(ev)) {
+        case error::connection_aborted:
+          return std::errc::connection_aborted;
+        case error::connection_refused:
+          return std::errc::connection_refused;
+        case error::connection_reset:
+          return std::errc::connection_reset;
+        default:
+          return std::error_condition(ev, *this);
+      }
+    }
+
+    bool equivalent(int code, const std::error_condition& cond) const noexcept override {
+      if (error_category::equivalent(code, cond)) {
+        return true;
+      }
+      switch (static_cast<error>(code)) {
+        case error::connection_aborted:
+          return cond == std::errc::connection_aborted
+              || cond == std::error_condition(ECONNABORTED, std::system_category());
+        case error::connection_refused:
+          return cond == std::errc::connection_refused
+              || cond == std::error_condition(ECONNREFUSED, std::system_category());
+        case error::connection_reset:
+          return cond == std::errc::connection_reset
+              || cond == std::error_condition(ECONNRESET, std::system_category());
+        default:
+          return false;
+      }
+    }
+
+    bool equivalent(const std::error_code& code, int cond) const noexcept override {
+      if (error_category::equivalent(code, cond)) {
+        return true;
+      }
+      switch (static_cast<error>(cond)) {
+        case error::connection_aborted:
+          return code == std::errc::connection_aborted
+              || code == std::error_code(ECONNABORTED, std::system_category());
+        case error::connection_refused:
+          return code == std::errc::connection_refused
+              || code == std::error_code(ECONNREFUSED, std::system_category());
+        case error::connection_reset:
+          return code == std::errc::connection_reset
+              || code == std::error_code(ECONNRESET, std::system_category());
+        default:
+          return false;
+      }
+    }
+  };
+  static category instance;
+  return instance;
+}
+
+} // namespace ceph::net
diff --git a/src/crimson/net/Errors.h b/src/crimson/net/Errors.h
new file mode 100644
index 00000000..d75082fd
--- /dev/null
+++ b/src/crimson/net/Errors.h
@@ -0,0 +1,54 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+/*
+ * Ceph - scalable distributed file system
+ *
+ * Copyright (C) 2017 Red Hat, Inc
+ *
+ * This is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License version 2.1, as published by the Free Software
+ * Foundation.  See file COPYING.
+ *
+ */
+
+#pragma once
+
+#include <system_error>
+
+namespace ceph::net {
+
+/// net error codes
+enum class error {
+  success = 0,
+  bad_connect_banner,
+  bad_peer_address,
+  negotiation_failure,
+  read_eof,
+  connection_aborted,
+  connection_refused,
+  connection_reset,
+};
+
+/// net error category
+const std::error_category& net_category();
+
+inline std::error_code make_error_code(error e)
+{
+  return {static_cast<int>(e), net_category()};
+}
+
+inline std::error_condition make_error_condition(error e)
+{
+  return {static_cast<int>(e), net_category()};
+}
+
+} // namespace ceph::net
+
+namespace std {
+
+/// enables implicit conversion to std::error_condition
+template <>
+struct is_error_condition_enum<ceph::net::error> : public true_type {};
+
+} // namespace std
diff --git a/src/crimson/net/Fwd.h b/src/crimson/net/Fwd.h
new file mode 100644
index 00000000..8a0a1c96
--- /dev/null
+++ b/src/crimson/net/Fwd.h
@@ -0,0 +1,52 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+/*
+ * Ceph - scalable distributed file system
+ *
+ * Copyright (C) 2017 Red Hat, Inc
+ *
+ * This is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License version 2.1, as published by the Free Software
+ * Foundation.  See file COPYING.
+ *
+ */
+
+#pragma once
+
+#include <seastar/core/shared_ptr.hh>
+#include <seastar/core/sharded.hh>
+
+#include "msg/msg_types.h"
+#include "msg/Message.h"
+
+using peer_type_t = int;
+using auth_proto_t = int;
+
+namespace ceph::net {
+
+using msgr_tag_t = uint8_t;
+
+class Connection;
+using ConnectionRef = seastar::shared_ptr<Connection>;
+// NOTE: ConnectionXRef should only be used in seastar world, because
+// lw_shared_ptr<> is not safe to be accessed by unpinned alien threads.
+using ConnectionXRef = seastar::lw_shared_ptr<seastar::foreign_ptr<ConnectionRef>>;
+
+class Dispatcher;
+
+class Messenger;
+
+template <typename T, typename... Args>
+seastar::future<T*> create_sharded(Args... args) {
+  auto sharded_obj = seastar::make_lw_shared<seastar::sharded<T>>();
+  return sharded_obj->start(args...).then([sharded_obj]() {
+      auto ret = &sharded_obj->local();
+      seastar::engine().at_exit([sharded_obj]() {
+          return sharded_obj->stop().finally([sharded_obj] {});
+        });
+      return ret;
+    });
+}
+
+} // namespace ceph::net
diff --git a/src/crimson/net/Messenger.cc b/src/crimson/net/Messenger.cc
new file mode 100644
index 00000000..7f8665ef
--- /dev/null
+++ b/src/crimson/net/Messenger.cc
@@ -0,0 +1,21 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+
+#include "Messenger.h"
+#include "SocketMessenger.h"
+
+namespace ceph::net {
+
+seastar::future<Messenger*>
+Messenger::create(const entity_name_t& name,
+                  const std::string& lname,
+                  const uint64_t nonce,
+                  const int master_sid)
+{
+  return create_sharded<SocketMessenger>(name, lname, nonce, master_sid)
+    .then([](Messenger *msgr) {
+      return msgr;
+    });
+}
+
+} // namespace ceph::net
diff --git a/src/crimson/net/Messenger.h b/src/crimson/net/Messenger.h
new file mode 100644
index 00000000..9d766cb0
--- /dev/null
+++ b/src/crimson/net/Messenger.h
@@ -0,0 +1,117 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+/*
+ * Ceph - scalable distributed file system
+ *
+ * Copyright (C) 2017 Red Hat, Inc
+ *
+ * This is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License version 2.1, as published by the Free Software
+ * Foundation.  See file COPYING.
+ *
+ */
+
+#pragma once
+
+#include <seastar/core/future.hh>
+
+#include "Fwd.h"
+#include "crimson/thread/Throttle.h"
+#include "msg/Policy.h"
+
+class AuthAuthorizer;
+
+namespace ceph::net {
+
+using Throttle = ceph::thread::Throttle;
+using SocketPolicy = ceph::net::Policy<Throttle>;
+
+class Messenger {
+  entity_name_t my_name;
+  entity_addrvec_t my_addrs;
+  uint32_t global_seq = 0;
+  uint32_t crc_flags = 0;
+
+ public:
+  Messenger(const entity_name_t& name)
+    : my_name(name)
+  {}
+  virtual ~Messenger() {}
+
+  const entity_name_t& get_myname() const { return my_name; }
+  const entity_addrvec_t& get_myaddrs() const { return my_addrs; }
+  entity_addr_t get_myaddr() const { return my_addrs.front(); }
+  virtual seastar::future<> set_myaddrs(const entity_addrvec_t& addrs) {
+    my_addrs = addrs;
+    return seastar::now();
+  }
+
+  /// bind to the given address
+  virtual seastar::future<> bind(const entity_addrvec_t& addr) = 0;
+
+  /// try to bind to the first unused port of given address
+  virtual seastar::future<> try_bind(const entity_addrvec_t& addr,
+                                     uint32_t min_port, uint32_t max_port) = 0;
+
+  /// start the messenger
+  virtual seastar::future<> start(Dispatcher *dispatcher) = 0;
+
+  /// either return an existing connection to the peer,
+  /// or a new pending connection
+  virtual seastar::future<ConnectionXRef>
+  connect(const entity_addr_t& peer_addr,
+          const entity_type_t& peer_type) = 0;
+
+  // wait for messenger shutdown
+  virtual seastar::future<> wait() = 0;
+
+  /// stop listenening and wait for all connections to close. safe to destruct
+  /// after this future becomes available
+  virtual seastar::future<> shutdown() = 0;
+
+  uint32_t get_global_seq(uint32_t old=0) {
+    if (old > global_seq) {
+      global_seq = old;
+    }
+    return ++global_seq;
+  }
+
+  uint32_t get_crc_flags() const {
+    return crc_flags;
+  }
+  void set_crc_data() {
+    crc_flags |= MSG_CRC_DATA;
+  }
+  void set_crc_header() {
+    crc_flags |= MSG_CRC_HEADER;
+  }
+
+  // get the local messenger shard if it is accessed by another core
+  virtual Messenger* get_local_shard() {
+    return this;
+  }
+
+  virtual void print(ostream& out) const = 0;
+
+  virtual void set_default_policy(const SocketPolicy& p) = 0;
+
+  virtual void set_policy(entity_type_t peer_type, const SocketPolicy& p) = 0;
+
+  virtual void set_policy_throttler(entity_type_t peer_type, Throttle* throttle) = 0;
+
+  static seastar::future<Messenger*>
+  create(const entity_name_t& name,
+         const std::string& lname,
+         const uint64_t nonce,
+         const int master_sid=-1);
+};
+
+inline ostream& operator<<(ostream& out, const Messenger& msgr) {
+  out << "[";
+  msgr.print(out);
+  out << "]";
+  return out;
+}
+
+} // namespace ceph::net
diff --git a/src/crimson/net/Socket.cc b/src/crimson/net/Socket.cc
new file mode 100644
index 00000000..a22e9b2e
--- /dev/null
+++ b/src/crimson/net/Socket.cc
@@ -0,0 +1,81 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+
+#include "Socket.h"
+
+#include "Errors.h"
+
+namespace ceph::net {
+
+namespace {
+
+// an input_stream consumer that reads buffer segments into a bufferlist up to
+// the given number of remaining bytes
+struct bufferlist_consumer {
+  bufferlist& bl;
+  size_t& remaining;
+
+  bufferlist_consumer(bufferlist& bl, size_t& remaining)
+    : bl(bl), remaining(remaining) {}
+
+  using tmp_buf = seastar::temporary_buffer<char>;
+  using consumption_result_type = typename seastar::input_stream<char>::consumption_result_type;
+
+  // consume some or all of a buffer segment
+  seastar::future<consumption_result_type> operator()(tmp_buf&& data) {
+    if (remaining >= data.size()) {
+      // consume the whole buffer
+      remaining -= data.size();
+      bl.append(buffer::create_foreign(std::move(data)));
+      if (remaining > 0) {
+        // return none to request more segments
+        return seastar::make_ready_future<consumption_result_type>(
+            seastar::continue_consuming{});
+      } else {
+        // return an empty buffer to singal that we're done
+        return seastar::make_ready_future<consumption_result_type>(
+            consumption_result_type::stop_consuming_type({}));
+      }
+    }
+    if (remaining > 0) {
+      // consume the front
+      bl.append(buffer::create_foreign(data.share(0, remaining)));
+      data.trim_front(remaining);
+      remaining = 0;
+    }
+    // give the rest back to signal that we're done
+    return seastar::make_ready_future<consumption_result_type>(
+        consumption_result_type::stop_consuming_type{std::move(data)});
+  };
+};
+
+} // anonymous namespace
+
+seastar::future<bufferlist> Socket::read(size_t bytes)
+{
+  if (bytes == 0) {
+    return seastar::make_ready_future<bufferlist>();
+  }
+  r.buffer.clear();
+  r.remaining = bytes;
+  return in.consume(bufferlist_consumer{r.buffer, r.remaining})
+    .then([this] {
+      if (r.remaining) { // throw on short reads
+        throw std::system_error(make_error_code(error::read_eof));
+      }
+      return seastar::make_ready_future<bufferlist>(std::move(r.buffer));
+    });
+}
+
+seastar::future<seastar::temporary_buffer<char>>
+Socket::read_exactly(size_t bytes) {
+  return in.read_exactly(bytes)
+    .then([this](auto buf) {
+      if (buf.empty()) {
+        throw std::system_error(make_error_code(error::read_eof));
+      }
+      return seastar::make_ready_future<tmp_buf>(std::move(buf));
+    });
+}
+
+} // namespace ceph::net
diff --git a/src/crimson/net/Socket.h b/src/crimson/net/Socket.h
new file mode 100644
index 00000000..c1a2ed59
--- /dev/null
+++ b/src/crimson/net/Socket.h
@@ -0,0 +1,59 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+
+#pragma once
+
+#include <seastar/core/reactor.hh>
+#include <seastar/net/packet.hh>
+
+#include "include/buffer.h"
+
+namespace ceph::net {
+
+class Socket
+{
+  const seastar::shard_id sid;
+  seastar::connected_socket socket;
+  seastar::input_stream<char> in;
+  seastar::output_stream<char> out;
+
+  /// buffer state for read()
+  struct {
+    bufferlist buffer;
+    size_t remaining;
+  } r;
+
+ public:
+  explicit Socket(seastar::connected_socket&& _socket)
+    : sid{seastar::engine().cpu_id()},
+      socket(std::move(_socket)),
+      in(socket.input()),
+      out(socket.output()) {}
+  Socket(Socket&& o) = delete;
+
+  /// read the requested number of bytes into a bufferlist
+  seastar::future<bufferlist> read(size_t bytes);
+  using tmp_buf = seastar::temporary_buffer<char>;
+  using packet = seastar::net::packet;
+  seastar::future<tmp_buf> read_exactly(size_t bytes);
+
+  seastar::future<> write(packet&& buf) {
+    return out.write(std::move(buf));
+  }
+  seastar::future<> flush() {
+    return out.flush();
+  }
+  seastar::future<> write_flush(packet&& buf) {
+    return out.write(std::move(buf)).then([this] { return out.flush(); });
+  }
+
+  /// Socket can only be closed once.
+  seastar::future<> close() {
+    return seastar::smp::submit_to(sid, [this] {
+        return seastar::when_all(
+          in.close(), out.close()).discard_result();
+      });
+  }
+};
+
+} // namespace ceph::net
diff --git a/src/crimson/net/SocketConnection.cc b/src/crimson/net/SocketConnection.cc
new file mode 100644
index 00000000..2907c486
--- /dev/null
+++ b/src/crimson/net/SocketConnection.cc
@@ -0,0 +1,972 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+/*
+ * Ceph - scalable distributed file system
+ *
+ * Copyright (C) 2017 Red Hat, Inc
+ *
+ * This is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License version 2.1, as published by the Free Software
+ * Foundation.  See file COPYING.
+ *
+ */
+
+#include "SocketConnection.h"
+
+#include <algorithm>
+#include <seastar/core/shared_future.hh>
+#include <seastar/core/sleep.hh>
+#include <seastar/net/packet.hh>
+
+#include "include/msgr.h"
+#include "include/random.h"
+#include "auth/Auth.h"
+#include "auth/AuthSessionHandler.h"
+
+#include "crimson/common/log.h"
+#include "Config.h"
+#include "Dispatcher.h"
+#include "Errors.h"
+#include "SocketMessenger.h"
+
+using namespace ceph::net;
+
+template <typename T>
+seastar::net::packet make_static_packet(const T& value) {
+    return { reinterpret_cast<const char*>(&value), sizeof(value) };
+}
+
+namespace {
+  seastar::logger& logger() {
+    return ceph::get_logger(ceph_subsys_ms);
+  }
+}
+
+SocketConnection::SocketConnection(SocketMessenger& messenger,
+                                   Dispatcher& dispatcher)
+  : messenger(messenger),
+    dispatcher(dispatcher),
+    send_ready(h.promise.get_future())
+{
+  ceph_assert(&messenger.container().local() == &messenger);
+}
+
+SocketConnection::~SocketConnection()
+{
+  ceph_assert(pending_dispatch.is_closed());
+}
+
+ceph::net::Messenger*
+SocketConnection::get_messenger() const {
+  return &messenger;
+}
+
+seastar::future<bool> SocketConnection::is_connected()
+{
+  return seastar::smp::submit_to(shard_id(), [this] {
+      return !send_ready.failed();
+    });
+}
+
+seastar::future<> SocketConnection::send(MessageRef msg)
+{
+  return seastar::smp::submit_to(shard_id(), [this, msg=std::move(msg)] {
+      if (state == state_t::closing)
+        return seastar::now();
+      return seastar::with_gate(pending_dispatch, [this, msg=std::move(msg)] {
+          return do_send(std::move(msg))
+            .handle_exception([this] (std::exception_ptr eptr) {
+              logger().warn("{} send fault: {}", *this, eptr);
+              close();
+            });
+        });
+    });
+}
+
+seastar::future<> SocketConnection::keepalive()
+{
+  return seastar::smp::submit_to(shard_id(), [this] {
+      if (state == state_t::closing)
+        return seastar::now();
+      return seastar::with_gate(pending_dispatch, [this] {
+          return do_keepalive()
+            .handle_exception([this] (std::exception_ptr eptr) {
+              logger().warn("{} keepalive fault: {}", *this, eptr);
+              close();
+            });
+        });
+    });
+}
+
+seastar::future<> SocketConnection::close()
+{
+  return seastar::smp::submit_to(shard_id(), [this] {
+      return do_close();
+    });
+}
+
+seastar::future<> SocketConnection::handle_tags()
+{
+  return seastar::keep_doing([this] {
+      // read the next tag
+      return socket->read_exactly(1)
+        .then([this] (auto buf) {
+          switch (buf[0]) {
+          case CEPH_MSGR_TAG_MSG:
+            return read_message();
+          case CEPH_MSGR_TAG_ACK:
+            return handle_ack();
+          case CEPH_MSGR_TAG_KEEPALIVE:
+            return seastar::now();
+          case CEPH_MSGR_TAG_KEEPALIVE2:
+            return handle_keepalive2();
+          case CEPH_MSGR_TAG_KEEPALIVE2_ACK:
+            return handle_keepalive2_ack();
+          case CEPH_MSGR_TAG_CLOSE:
+            logger().info("{} got tag close", *this);
+            throw std::system_error(make_error_code(error::connection_aborted));
+          default:
+            logger().error("{} got unknown msgr tag {}", *this, static_cast<int>(buf[0]));
+            throw std::system_error(make_error_code(error::read_eof));
+          }
+        });
+    });
+}
+
+seastar::future<> SocketConnection::handle_ack()
+{
+  return socket->read_exactly(sizeof(ceph_le64))
+    .then([this] (auto buf) {
+      auto seq = reinterpret_cast<const ceph_le64*>(buf.get());
+      discard_up_to(&sent, *seq);
+    });
+}
+
+void SocketConnection::discard_up_to(std::queue<MessageRef>* queue,
+                                     seq_num_t seq)
+{
+  while (!queue->empty() &&
+         queue->front()->get_seq() < seq) {
+    queue->pop();
+  }
+}
+
+void SocketConnection::requeue_sent()
+{
+  out_seq -= sent.size();
+  while (!sent.empty()) {
+    auto m = sent.front();
+    sent.pop();
+    out_q.push(std::move(m));
+  }
+}
+
+seastar::future<> SocketConnection::maybe_throttle()
+{
+  if (!policy.throttler_bytes) {
+    return seastar::now();
+  }
+  const auto to_read = (m.header.front_len +
+                        m.header.middle_len +
+                        m.header.data_len);
+  return policy.throttler_bytes->get(to_read);
+}
+
+seastar::future<> SocketConnection::read_message()
+{
+  return socket->read(sizeof(m.header))
+    .then([this] (bufferlist bl) {
+      // throttle the traffic, maybe
+      auto p = bl.cbegin();
+      ::decode(m.header, p);
+      return maybe_throttle();
+    }).then([this] {
+      // read front
+      return socket->read(m.header.front_len);
+    }).then([this] (bufferlist bl) {
+      m.front = std::move(bl);
+      // read middle
+      return socket->read(m.header.middle_len);
+    }).then([this] (bufferlist bl) {
+      m.middle = std::move(bl);
+      // read data
+      return socket->read(m.header.data_len);
+    }).then([this] (bufferlist bl) {
+      m.data = std::move(bl);
+      // read footer
+      return socket->read(sizeof(m.footer));
+    }).then([this] (bufferlist bl) {
+      auto p = bl.cbegin();
+      ::decode(m.footer, p);
+      auto msg = ::decode_message(nullptr, 0, m.header, m.footer,
+                                  m.front, m.middle, m.data, nullptr);
+      // TODO: set time stamps
+      msg->set_byte_throttler(policy.throttler_bytes);
+
+      if (!update_rx_seq(msg->get_seq())) {
+        // skip this message
+        return;
+      }
+
+      constexpr bool add_ref = false; // Message starts with 1 ref
+      // TODO: change MessageRef with foreign_ptr
+      auto msg_ref = MessageRef{msg, add_ref};
+      // start dispatch, ignoring exceptions from the application layer
+      seastar::with_gate(pending_dispatch, [this, msg = std::move(msg_ref)] {
+          return dispatcher.ms_dispatch(
+              seastar::static_pointer_cast<SocketConnection>(shared_from_this()),
+              std::move(msg))
+            .handle_exception([this] (std::exception_ptr eptr) {
+              logger().error("{} ms_dispatch caught exception: {}", *this, eptr);
+              ceph_assert(false);
+            });
+        });
+    });
+}
+
+bool SocketConnection::update_rx_seq(seq_num_t seq)
+{
+  if (seq <= in_seq) {
+    if (HAVE_FEATURE(features, RECONNECT_SEQ) &&
+        conf.ms_die_on_old_message) {
+      ceph_abort_msg("old msgs despite reconnect_seq feature");
+    }
+    return false;
+  } else if (seq > in_seq + 1) {
+    if (conf.ms_die_on_skipped_message) {
+      ceph_abort_msg("skipped incoming seq");
+    }
+    return false;
+  } else {
+    in_seq = seq;
+    return true;
+  }
+}
+
+seastar::future<> SocketConnection::write_message(MessageRef msg)
+{
+  msg->set_seq(++out_seq);
+  auto& header = msg->get_header();
+  header.src = messenger.get_myname();
+  msg->encode(features, messenger.get_crc_flags());
+  bufferlist bl;
+  bl.append(CEPH_MSGR_TAG_MSG);
+  bl.append((const char*)&header, sizeof(header));
+  bl.append(msg->get_payload());
+  bl.append(msg->get_middle());
+  bl.append(msg->get_data());
+  auto& footer = msg->get_footer();
+  if (HAVE_FEATURE(features, MSG_AUTH)) {
+    bl.append((const char*)&footer, sizeof(footer));
+  } else {
+    ceph_msg_footer_old old_footer;
+    if (messenger.get_crc_flags() & MSG_CRC_HEADER) {
+      old_footer.front_crc = footer.front_crc;
+      old_footer.middle_crc = footer.middle_crc;
+    } else {
+      old_footer.front_crc = old_footer.middle_crc = 0;
+    }
+    if (messenger.get_crc_flags() & MSG_CRC_DATA) {
+      old_footer.data_crc = footer.data_crc;
+    } else {
+      old_footer.data_crc = 0;
+    }
+    old_footer.flags = footer.flags;
+    bl.append((const char*)&old_footer, sizeof(old_footer));
+  }
+  // write as a seastar::net::packet
+  return socket->write_flush(std::move(bl));
+  // TODO: lossless policy
+  //  .then([this, msg = std::move(msg)] {
+  //    if (!policy.lossy) {
+  //      sent.push(std::move(msg));
+  //    }
+  //  });
+}
+
+seastar::future<> SocketConnection::do_send(MessageRef msg)
+{
+  // chain the message after the last message is sent
+  // TODO: retry send for lossless connection
+  seastar::shared_future<> f = send_ready.then(
+    [this, msg = std::move(msg)] {
+      if (state == state_t::closing)
+        return seastar::now();
+      return write_message(std::move(msg));
+    });
+
+  // chain any later messages after this one completes
+  send_ready = f.get_future();
+  // allow the caller to wait on the same future
+  return f.get_future();
+}
+
+seastar::future<> SocketConnection::do_keepalive()
+{
+  // TODO: retry keepalive for lossless connection
+  seastar::shared_future<> f = send_ready.then([this] {
+      if (state == state_t::closing)
+        return seastar::now();
+      k.req.stamp = ceph::coarse_real_clock::to_ceph_timespec(
+        ceph::coarse_real_clock::now());
+      return socket->write_flush(make_static_packet(k.req));
+    });
+  send_ready = f.get_future();
+  return f.get_future();
+}
+
+seastar::future<> SocketConnection::do_close()
+{
+  if (state == state_t::closing) {
+    // already closing
+    assert(close_ready.valid());
+    return close_ready.get_future();
+  }
+
+  // unregister_conn() drops a reference, so hold another until completion
+  auto cleanup = [conn_ref = shared_from_this(), this] {
+      logger().debug("{} closed!", *this);
+    };
+
+  if (state == state_t::accepting) {
+    messenger.unaccept_conn(seastar::static_pointer_cast<SocketConnection>(shared_from_this()));
+  } else if (state >= state_t::connecting && state < state_t::closing) {
+    messenger.unregister_conn(seastar::static_pointer_cast<SocketConnection>(shared_from_this()));
+  } else {
+    // cannot happen
+    ceph_assert(false);
+  }
+
+  // close_ready become valid only after state is state_t::closing
+  assert(!close_ready.valid());
+
+  if (socket) {
+    close_ready = socket->close()
+      .then([this] {
+        return pending_dispatch.close();
+      }).finally(std::move(cleanup));
+  } else {
+    ceph_assert(state == state_t::connecting);
+    close_ready = pending_dispatch.close().finally(std::move(cleanup));
+  }
+  logger().debug("{} trigger closing, was {}", *this, static_cast<int>(state));
+  state = state_t::closing;
+  return close_ready.get_future();
+}
+
+// handshake
+
+/// store the banner in a non-const string for buffer::create_static()
+static char banner[] = CEPH_BANNER;
+constexpr size_t banner_size = sizeof(CEPH_BANNER)-1;
+
+constexpr size_t client_header_size = banner_size + sizeof(ceph_entity_addr);
+constexpr size_t server_header_size = banner_size + 2 * sizeof(ceph_entity_addr);
+
+WRITE_RAW_ENCODER(ceph_msg_connect);
+WRITE_RAW_ENCODER(ceph_msg_connect_reply);
+
+std::ostream& operator<<(std::ostream& out, const ceph_msg_connect& c)
+{
+  return out << "connect{features=" << std::hex << c.features << std::dec
+      << " host_type=" << c.host_type
+      << " global_seq=" << c.global_seq
+      << " connect_seq=" << c.connect_seq
+      << " protocol_version=" << c.protocol_version
+      << " authorizer_protocol=" << c.authorizer_protocol
+      << " authorizer_len=" << c.authorizer_len
+      << " flags=" << std::hex << static_cast<uint16_t>(c.flags) << std::dec << '}';
+}
+
+std::ostream& operator<<(std::ostream& out, const ceph_msg_connect_reply& r)
+{
+  return out << "connect_reply{tag=" << static_cast<uint16_t>(r.tag)
+      << " features=" << std::hex << r.features << std::dec
+      << " global_seq=" << r.global_seq
+      << " connect_seq=" << r.connect_seq
+      << " protocol_version=" << r.protocol_version
+      << " authorizer_len=" << r.authorizer_len
+      << " flags=" << std::hex << static_cast<uint16_t>(r.flags) << std::dec << '}';
+}
+
+// check that the buffer starts with a valid banner without requiring it to
+// be contiguous in memory
+static void validate_banner(bufferlist::const_iterator& p)
+{
+  auto b = std::cbegin(banner);
+  auto end = b + banner_size;
+  while (b != end) {
+    const char *buf{nullptr};
+    auto remaining = std::distance(b, end);
+    auto len = p.get_ptr_and_advance(remaining, &buf);
+    if (!std::equal(buf, buf + len, b)) {
+      throw std::system_error(make_error_code(error::bad_connect_banner));
+    }
+    b += len;
+  }
+}
+
+// make sure that we agree with the peer about its address
+static void validate_peer_addr(const entity_addr_t& addr,
+                               const entity_addr_t& expected)
+{
+  if (addr == expected) {
+    return;
+  }
+  // ok if server bound anonymously, as long as port/nonce match
+  if (addr.is_blank_ip() &&
+      addr.get_port() == expected.get_port() &&
+      addr.get_nonce() == expected.get_nonce()) {
+    return;
+  } else {
+    throw std::system_error(make_error_code(error::bad_peer_address));
+  }
+}
+
+/// return a static bufferptr to the given object
+template <typename T>
+bufferptr create_static(T& obj)
+{
+  return buffer::create_static(sizeof(obj), reinterpret_cast<char*>(&obj));
+}
+
+bool SocketConnection::require_auth_feature() const
+{
+  if (h.connect.authorizer_protocol != CEPH_AUTH_CEPHX) {
+    return false;
+  }
+  if (conf.cephx_require_signatures) {
+    return true;
+  }
+  if (h.connect.host_type == CEPH_ENTITY_TYPE_OSD ||
+      h.connect.host_type == CEPH_ENTITY_TYPE_MDS) {
+    return conf.cephx_cluster_require_signatures;
+  } else {
+    return conf.cephx_service_require_signatures;
+  }
+}
+
+uint32_t SocketConnection::get_proto_version(entity_type_t peer_type, bool connect) const
+{
+  constexpr entity_type_t my_type = CEPH_ENTITY_TYPE_OSD;
+  // see also OSD.h, unlike other connection of simple/async messenger,
+  // crimson msgr is only used by osd
+  constexpr uint32_t CEPH_OSD_PROTOCOL = 10;
+  if (peer_type == my_type) {
+    // internal
+    return CEPH_OSD_PROTOCOL;
+  } else {
+    // public
+    switch (connect ? peer_type : my_type) {
+      case CEPH_ENTITY_TYPE_OSD: return CEPH_OSDC_PROTOCOL;
+      case CEPH_ENTITY_TYPE_MDS: return CEPH_MDSC_PROTOCOL;
+      case CEPH_ENTITY_TYPE_MON: return CEPH_MONC_PROTOCOL;
+      default: return 0;
+    }
+  }
+}
+
+seastar::future<seastar::stop_iteration>
+SocketConnection::repeat_handle_connect()
+{
+  return socket->read(sizeof(h.connect))
+    .then([this](bufferlist bl) {
+      auto p = bl.cbegin();
+      ::decode(h.connect, p);
+      peer_type = h.connect.host_type;
+      return socket->read(h.connect.authorizer_len);
+    }).then([this] (bufferlist authorizer) {
+      if (h.connect.protocol_version != get_proto_version(h.connect.host_type, false)) {
+      	return seastar::make_ready_future<msgr_tag_t, bufferlist>(
+            CEPH_MSGR_TAG_BADPROTOVER, bufferlist{});
+      }
+      if (require_auth_feature()) {
+      	policy.features_required |= CEPH_FEATURE_MSG_AUTH;
+      }
+      if (auto feat_missing = policy.features_required & ~(uint64_t)h.connect.features;
+      	  feat_missing != 0) {
+        return seastar::make_ready_future<msgr_tag_t, bufferlist>(
+            CEPH_MSGR_TAG_FEATURES, bufferlist{});
+      }
+      return dispatcher.ms_verify_authorizer(peer_type,
+                                             h.connect.authorizer_protocol,
+                                             authorizer);
+    }).then([this] (ceph::net::msgr_tag_t tag, bufferlist&& authorizer_reply) {
+      memset(&h.reply, 0, sizeof(h.reply));
+      if (tag) {
+	return send_connect_reply(tag, std::move(authorizer_reply));
+      }
+      if (auto existing = messenger.lookup_conn(peer_addr); existing) {
+	return handle_connect_with_existing(existing, std::move(authorizer_reply));
+      } else if (h.connect.connect_seq > 0) {
+	return send_connect_reply(CEPH_MSGR_TAG_RESETSESSION,
+				  std::move(authorizer_reply));
+      }
+      h.connect_seq = h.connect.connect_seq + 1;
+      h.peer_global_seq = h.connect.global_seq;
+      set_features((uint64_t)policy.features_supported & (uint64_t)h.connect.features);
+      // TODO: cct
+      return send_connect_reply_ready(CEPH_MSGR_TAG_READY, std::move(authorizer_reply));
+    });
+}
+
+seastar::future<seastar::stop_iteration>
+SocketConnection::send_connect_reply(msgr_tag_t tag,
+                                     bufferlist&& authorizer_reply)
+{
+  h.reply.tag = tag;
+  h.reply.features = static_cast<uint64_t>((h.connect.features &
+					    policy.features_supported) |
+					   policy.features_required);
+  h.reply.authorizer_len = authorizer_reply.length();
+  return socket->write(make_static_packet(h.reply))
+    .then([this, reply=std::move(authorizer_reply)]() mutable {
+      return socket->write_flush(std::move(reply));
+    }).then([] {
+      return stop_t::no;
+    });
+}
+
+seastar::future<seastar::stop_iteration>
+SocketConnection::send_connect_reply_ready(msgr_tag_t tag,
+                                           bufferlist&& authorizer_reply)
+{
+  h.global_seq = messenger.get_global_seq();
+  h.reply.tag = tag;
+  h.reply.features = policy.features_supported;
+  h.reply.global_seq = h.global_seq;
+  h.reply.connect_seq = h.connect_seq;
+  h.reply.flags = 0;
+  if (policy.lossy) {
+    h.reply.flags = h.reply.flags | CEPH_MSG_CONNECT_LOSSY;
+  }
+  h.reply.authorizer_len = authorizer_reply.length();
+  return socket->write(make_static_packet(h.reply))
+    .then([this, reply=std::move(authorizer_reply)]() mutable {
+      if (reply.length()) {
+        return socket->write(std::move(reply));
+      } else {
+        return seastar::now();
+      }
+    }).then([this] {
+      if (h.reply.tag == CEPH_MSGR_TAG_SEQ) {
+        return socket->write_flush(make_static_packet(in_seq))
+          .then([this] {
+            return socket->read_exactly(sizeof(seq_num_t));
+          }).then([this] (auto buf) {
+            auto acked_seq = reinterpret_cast<const seq_num_t*>(buf.get());
+            discard_up_to(&out_q, *acked_seq);
+          });
+      } else {
+        return socket->flush();
+      }
+    }).then([this] {
+      return stop_t::yes;
+    });
+}
+
+seastar::future<>
+SocketConnection::handle_keepalive2()
+{
+  return socket->read_exactly(sizeof(ceph_timespec))
+    .then([this] (auto buf) {
+      k.ack.stamp = *reinterpret_cast<const ceph_timespec*>(buf.get());
+      seastar::shared_future<> f = send_ready.then([this] {
+          logger().debug("{} keepalive2 {}", *this, k.ack.stamp.tv_sec);
+          return socket->write_flush(make_static_packet(k.ack));
+        });
+      send_ready = f.get_future();
+      return f.get_future();
+    });
+}
+
+seastar::future<>
+SocketConnection::handle_keepalive2_ack()
+{
+  return socket->read_exactly(sizeof(ceph_timespec))
+    .then([this] (auto buf) {
+      auto t = reinterpret_cast<const ceph_timespec*>(buf.get());
+      k.ack_stamp = *t;
+      logger().debug("{} keepalive2 ack {}", *this, t->tv_sec);
+    });
+}
+
+seastar::future<seastar::stop_iteration>
+SocketConnection::handle_connect_with_existing(SocketConnectionRef existing, bufferlist&& authorizer_reply)
+{
+  if (h.connect.global_seq < existing->peer_global_seq()) {
+    h.reply.global_seq = existing->peer_global_seq();
+    return send_connect_reply(CEPH_MSGR_TAG_RETRY_GLOBAL);
+  } else if (existing->is_lossy()) {
+    return replace_existing(existing, std::move(authorizer_reply));
+  } else if (h.connect.connect_seq == 0 && existing->connect_seq() > 0) {
+    return replace_existing(existing, std::move(authorizer_reply), true);
+  } else if (h.connect.connect_seq < existing->connect_seq()) {
+    // old attempt, or we sent READY but they didn't get it.
+    h.reply.connect_seq = existing->connect_seq() + 1;
+    return send_connect_reply(CEPH_MSGR_TAG_RETRY_SESSION);
+  } else if (h.connect.connect_seq == existing->connect_seq()) {
+    // if the existing connection successfully opened, and/or
+    // subsequently went to standby, then the peer should bump
+    // their connect_seq and retry: this is not a connection race
+    // we need to resolve here.
+    if (existing->get_state() == state_t::open ||
+	existing->get_state() == state_t::standby) {
+      if (policy.resetcheck && existing->connect_seq() == 0) {
+	return replace_existing(existing, std::move(authorizer_reply));
+      } else {
+	h.reply.connect_seq = existing->connect_seq() + 1;
+	return send_connect_reply(CEPH_MSGR_TAG_RETRY_SESSION);
+      }
+    } else if (peer_addr < messenger.get_myaddr() ||
+	       existing->is_server_side()) {
+      // incoming wins
+      return replace_existing(existing, std::move(authorizer_reply));
+    } else {
+      return send_connect_reply(CEPH_MSGR_TAG_WAIT);
+    }
+  } else if (policy.resetcheck &&
+	     existing->connect_seq() == 0) {
+    return send_connect_reply(CEPH_MSGR_TAG_RESETSESSION);
+  } else {
+    return replace_existing(existing, std::move(authorizer_reply));
+  }
+}
+
+seastar::future<seastar::stop_iteration>
+SocketConnection::replace_existing(SocketConnectionRef existing,
+                                   bufferlist&& authorizer_reply,
+                                   bool is_reset_from_peer)
+{
+  msgr_tag_t reply_tag;
+  if (HAVE_FEATURE(h.connect.features, RECONNECT_SEQ) &&
+      !is_reset_from_peer) {
+    reply_tag = CEPH_MSGR_TAG_SEQ;
+  } else {
+    reply_tag = CEPH_MSGR_TAG_READY;
+  }
+  messenger.unregister_conn(existing);
+  if (!existing->is_lossy()) {
+    // reset the in_seq if this is a hard reset from peer,
+    // otherwise we respect our original connection's value
+    in_seq = is_reset_from_peer ? 0 : existing->rx_seq_num();
+    // steal outgoing queue and out_seq
+    existing->requeue_sent();
+    std::tie(out_seq, out_q) = existing->get_out_queue();
+  }
+  return send_connect_reply_ready(reply_tag, std::move(authorizer_reply));
+}
+
+seastar::future<seastar::stop_iteration>
+SocketConnection::handle_connect_reply(msgr_tag_t tag)
+{
+  switch (tag) {
+  case CEPH_MSGR_TAG_FEATURES:
+    logger().error("{} connect protocol feature mispatch", __func__);
+    throw std::system_error(make_error_code(error::negotiation_failure));
+  case CEPH_MSGR_TAG_BADPROTOVER:
+    logger().error("{} connect protocol version mispatch", __func__);
+    throw std::system_error(make_error_code(error::negotiation_failure));
+  case CEPH_MSGR_TAG_BADAUTHORIZER:
+    logger().error("{} got bad authorizer", __func__);
+    throw std::system_error(make_error_code(error::negotiation_failure));
+  case CEPH_MSGR_TAG_RESETSESSION:
+    reset_session();
+    return seastar::make_ready_future<stop_t>(stop_t::no);
+  case CEPH_MSGR_TAG_RETRY_GLOBAL:
+    h.global_seq = messenger.get_global_seq(h.reply.global_seq);
+    return seastar::make_ready_future<stop_t>(stop_t::no);
+  case CEPH_MSGR_TAG_RETRY_SESSION:
+    ceph_assert(h.reply.connect_seq > h.connect_seq);
+    h.connect_seq = h.reply.connect_seq;
+    return seastar::make_ready_future<stop_t>(stop_t::no);
+  case CEPH_MSGR_TAG_WAIT:
+    // TODO: state wait
+    throw std::system_error(make_error_code(error::negotiation_failure));
+  case CEPH_MSGR_TAG_SEQ:
+  case CEPH_MSGR_TAG_READY:
+    if (auto missing = (policy.features_required & ~(uint64_t)h.reply.features);
+        missing) {
+      logger().error("{} missing required features", __func__);
+      throw std::system_error(make_error_code(error::negotiation_failure));
+    }
+    return seastar::futurize_apply([this, tag] {
+        if (tag == CEPH_MSGR_TAG_SEQ) {
+          return socket->read_exactly(sizeof(seq_num_t))
+            .then([this] (auto buf) {
+              auto acked_seq = reinterpret_cast<const seq_num_t*>(buf.get());
+              discard_up_to(&out_q, *acked_seq);
+              return socket->write_flush(make_static_packet(in_seq));
+            });
+        }
+        // tag CEPH_MSGR_TAG_READY
+        return seastar::now();
+      }).then([this] {
+        // hooray!
+        h.peer_global_seq = h.reply.global_seq;
+        policy.lossy = h.reply.flags & CEPH_MSG_CONNECT_LOSSY;
+        h.connect_seq++;
+        h.backoff = 0ms;
+        set_features(h.reply.features & h.connect.features);
+        if (h.authorizer) {
+          session_security.reset(
+              get_auth_session_handler(nullptr,
+                                       h.authorizer->protocol,
+                                       h.authorizer->session_key,
+                                       features));
+        }
+        h.authorizer.reset();
+        return seastar::make_ready_future<stop_t>(stop_t::yes);
+      });
+    break;
+  default:
+    // unknown tag
+    logger().error("{} got unknown tag", __func__, int(tag));
+    throw std::system_error(make_error_code(error::negotiation_failure));
+  }
+}
+
+void SocketConnection::reset_session()
+{
+  decltype(out_q){}.swap(out_q);
+  decltype(sent){}.swap(sent);
+  in_seq = 0;
+  h.connect_seq = 0;
+  if (HAVE_FEATURE(features, MSG_AUTH)) {
+    // Set out_seq to a random value, so CRC won't be predictable.
+    // Constant to limit starting sequence number to 2^31.  Nothing special
+    // about it, just a big number.
+    constexpr uint64_t SEQ_MASK = 0x7fffffff;
+    out_seq = ceph::util::generate_random_number<uint64_t>(0, SEQ_MASK);
+  } else {
+    // previously, seq #'s always started at 0.
+    out_seq = 0;
+  }
+}
+
+seastar::future<seastar::stop_iteration>
+SocketConnection::repeat_connect()
+{
+  // encode ceph_msg_connect
+  memset(&h.connect, 0, sizeof(h.connect));
+  h.connect.features = policy.features_supported;
+  h.connect.host_type = messenger.get_myname().type();
+  h.connect.global_seq = h.global_seq;
+  h.connect.connect_seq = h.connect_seq;
+  h.connect.protocol_version = get_proto_version(peer_type, true);
+  // this is fyi, actually, server decides!
+  h.connect.flags = policy.lossy ? CEPH_MSG_CONNECT_LOSSY : 0;
+
+  return dispatcher.ms_get_authorizer(peer_type)
+    .then([this](auto&& auth) {
+      h.authorizer = std::move(auth);
+      bufferlist bl;
+      if (h.authorizer) {
+        h.connect.authorizer_protocol = h.authorizer->protocol;
+        h.connect.authorizer_len = h.authorizer->bl.length();
+        bl.append(create_static(h.connect));
+        bl.append(h.authorizer->bl);
+      } else {
+        h.connect.authorizer_protocol = 0;
+        h.connect.authorizer_len = 0;
+        bl.append(create_static(h.connect));
+      };
+      return socket->write_flush(std::move(bl));
+    }).then([this] {
+     // read the reply
+      return socket->read(sizeof(h.reply));
+    }).then([this] (bufferlist bl) {
+      auto p = bl.cbegin();
+      ::decode(h.reply, p);
+      ceph_assert(p.end());
+      return socket->read(h.reply.authorizer_len);
+    }).then([this] (bufferlist bl) {
+      if (h.authorizer) {
+        auto reply = bl.cbegin();
+        if (!h.authorizer->verify_reply(reply, nullptr)) {
+          logger().error("{} authorizer failed to verify reply", __func__);
+          throw std::system_error(make_error_code(error::negotiation_failure));
+        }
+      }
+      return handle_connect_reply(h.reply.tag);
+    });
+}
+
+void
+SocketConnection::start_connect(const entity_addr_t& _peer_addr,
+                                const entity_type_t& _peer_type)
+{
+  ceph_assert(state == state_t::none);
+  ceph_assert(!socket);
+  peer_addr = _peer_addr;
+  peer_type = _peer_type;
+  messenger.register_conn(seastar::static_pointer_cast<SocketConnection>(shared_from_this()));
+  logger().debug("{} trigger connecting, was {}", *this, static_cast<int>(state));
+  state = state_t::connecting;
+  seastar::with_gate(pending_dispatch, [this] {
+      return seastar::connect(peer_addr.in4_addr())
+        .then([this](seastar::connected_socket fd) {
+          if (state == state_t::closing) {
+            fd.shutdown_input();
+            fd.shutdown_output();
+            throw std::system_error(make_error_code(error::connection_aborted));
+          }
+          socket = seastar::make_foreign(std::make_unique<Socket>(std::move(fd)));
+          // read server's handshake header
+          return socket->read(server_header_size);
+        }).then([this] (bufferlist headerbl) {
+          auto p = headerbl.cbegin();
+          validate_banner(p);
+          entity_addr_t saddr, caddr;
+          ::decode(saddr, p);
+          ::decode(caddr, p);
+          ceph_assert(p.end());
+          validate_peer_addr(saddr, peer_addr);
+
+          side = side_t::connector;
+          socket_port = caddr.get_port();
+          return messenger.learned_addr(caddr);
+        }).then([this] {
+          // encode/send client's handshake header
+          bufferlist bl;
+          bl.append(buffer::create_static(banner_size, banner));
+          ::encode(messenger.get_myaddr(), bl, 0);
+          h.global_seq = messenger.get_global_seq();
+          return socket->write_flush(std::move(bl));
+        }).then([=] {
+          return seastar::repeat([this] {
+            return repeat_connect();
+          });
+        }).then([this] {
+          // notify the dispatcher and allow them to reject the connection
+          return dispatcher.ms_handle_connect(seastar::static_pointer_cast<SocketConnection>(shared_from_this()));
+        }).then([this] {
+          execute_open();
+        }).handle_exception([this] (std::exception_ptr eptr) {
+          // TODO: handle fault in the connecting state
+          logger().warn("{} connecting fault: {}", *this, eptr);
+          h.promise.set_value();
+          close();
+        });
+    });
+}
+
+void
+SocketConnection::start_accept(seastar::foreign_ptr<std::unique_ptr<Socket>>&& sock,
+                               const entity_addr_t& _peer_addr)
+{
+  ceph_assert(state == state_t::none);
+  ceph_assert(!socket);
+  peer_addr.u = _peer_addr.u;
+  peer_addr.set_port(0);
+  side = side_t::acceptor;
+  socket_port = _peer_addr.get_port();
+  socket = std::move(sock);
+  messenger.accept_conn(seastar::static_pointer_cast<SocketConnection>(shared_from_this()));
+  logger().debug("{} trigger accepting, was {}", *this, static_cast<int>(state));
+  state = state_t::accepting;
+  seastar::with_gate(pending_dispatch, [this, _peer_addr] {
+      // encode/send server's handshake header
+      bufferlist bl;
+      bl.append(buffer::create_static(banner_size, banner));
+      ::encode(messenger.get_myaddr(), bl, 0);
+      ::encode(_peer_addr, bl, 0);
+      return socket->write_flush(std::move(bl))
+        .then([this] {
+          // read client's handshake header and connect request
+          return socket->read(client_header_size);
+        }).then([this] (bufferlist bl) {
+          auto p = bl.cbegin();
+          validate_banner(p);
+          entity_addr_t addr;
+          ::decode(addr, p);
+          ceph_assert(p.end());
+          peer_addr.set_type(addr.get_type());
+          peer_addr.set_port(addr.get_port());
+          peer_addr.set_nonce(addr.get_nonce());
+          return seastar::repeat([this] {
+            return repeat_handle_connect();
+          });
+        }).then([this] {
+          // notify the dispatcher and allow them to reject the connection
+          return dispatcher.ms_handle_accept(seastar::static_pointer_cast<SocketConnection>(shared_from_this()));
+        }).then([this] {
+          messenger.register_conn(seastar::static_pointer_cast<SocketConnection>(shared_from_this()));
+          messenger.unaccept_conn(seastar::static_pointer_cast<SocketConnection>(shared_from_this()));
+          execute_open();
+        }).handle_exception([this] (std::exception_ptr eptr) {
+          // TODO: handle fault in the accepting state
+          logger().warn("{} accepting fault: {}", *this, eptr);
+          h.promise.set_value();
+          close();
+        });
+    });
+}
+
+void
+SocketConnection::execute_open()
+{
+  logger().debug("{} trigger open, was {}", *this, static_cast<int>(state));
+  state = state_t::open;
+  // satisfy the handshake's promise
+  h.promise.set_value();
+  seastar::with_gate(pending_dispatch, [this] {
+      // start background processing of tags
+      return handle_tags()
+        .handle_exception_type([this] (const std::system_error& e) {
+          logger().warn("{} open fault: {}", *this, e);
+          if (e.code() == error::connection_aborted ||
+              e.code() == error::connection_reset) {
+            return dispatcher.ms_handle_reset(seastar::static_pointer_cast<SocketConnection>(shared_from_this()))
+              .then([this] {
+                close();
+              });
+          } else if (e.code() == error::read_eof) {
+            return dispatcher.ms_handle_remote_reset(seastar::static_pointer_cast<SocketConnection>(shared_from_this()))
+              .then([this] {
+                close();
+              });
+          } else {
+            throw e;
+          }
+        }).handle_exception([this] (std::exception_ptr eptr) {
+          // TODO: handle fault in the open state
+          logger().warn("{} open fault: {}", *this, eptr);
+          close();
+        });
+    });
+}
+
+seastar::future<> SocketConnection::fault()
+{
+  if (policy.lossy) {
+    messenger.unregister_conn(seastar::static_pointer_cast<SocketConnection>(shared_from_this()));
+  }
+  if (h.backoff.count()) {
+    h.backoff += h.backoff;
+  } else {
+    h.backoff = conf.ms_initial_backoff;
+  }
+  if (h.backoff > conf.ms_max_backoff) {
+    h.backoff = conf.ms_max_backoff;
+  }
+  return seastar::sleep(h.backoff);
+}
+
+seastar::shard_id SocketConnection::shard_id() const {
+  return messenger.shard_id();
+}
+
+void SocketConnection::print(ostream& out) const {
+    messenger.print(out);
+    if (side == side_t::none) {
+      out << " >> " << peer_addr;
+    } else if (side == side_t::acceptor) {
+      out << " >> " << peer_addr
+          << "@" << socket_port;
+    } else { // side == side_t::connector
+      out << "@" << socket_port
+          << " >> " << peer_addr;
+    }
+}
diff --git a/src/crimson/net/SocketConnection.h b/src/crimson/net/SocketConnection.h
new file mode 100644
index 00000000..62cc77d5
--- /dev/null
+++ b/src/crimson/net/SocketConnection.h
@@ -0,0 +1,235 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+/*
+ * Ceph - scalable distributed file system
+ *
+ * Copyright (C) 2017 Red Hat, Inc
+ *
+ * This is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License version 2.1, as published by the Free Software
+ * Foundation.  See file COPYING.
+ *
+ */
+
+#pragma once
+
+#include <seastar/core/gate.hh>
+#include <seastar/core/reactor.hh>
+#include <seastar/core/shared_future.hh>
+#include <seastar/core/sharded.hh>
+
+#include "msg/Policy.h"
+#include "Connection.h"
+#include "Socket.h"
+#include "crimson/thread/Throttle.h"
+
+class AuthAuthorizer;
+class AuthSessionHandler;
+
+namespace ceph::net {
+
+using stop_t = seastar::stop_iteration;
+
+class SocketMessenger;
+class SocketConnection;
+using SocketConnectionRef = seastar::shared_ptr<SocketConnection>;
+
+class SocketConnection : public Connection {
+  SocketMessenger& messenger;
+  seastar::foreign_ptr<std::unique_ptr<Socket>> socket;
+  Dispatcher& dispatcher;
+  seastar::gate pending_dispatch;
+
+  // if acceptor side, socket_port is different from peer_addr.get_port();
+  // if connector side, socket_port is different from my_addr.get_port().
+  enum class side_t {
+    none,
+    acceptor,
+    connector
+  };
+  side_t side = side_t::none;
+  uint16_t socket_port = 0;
+
+  enum class state_t {
+    none,
+    accepting,
+    connecting,
+    open,
+    standby,
+    wait,
+    closing
+  };
+  state_t state = state_t::none;
+
+  /// become valid only when state is state_t::closing
+  seastar::shared_future<> close_ready;
+
+  /// state for handshake
+  struct Handshake {
+    ceph_msg_connect connect;
+    ceph_msg_connect_reply reply;
+    std::unique_ptr<AuthAuthorizer> authorizer;
+    std::chrono::milliseconds backoff;
+    uint32_t connect_seq = 0;
+    uint32_t peer_global_seq = 0;
+    uint32_t global_seq;
+    seastar::promise<> promise;
+  } h;
+
+  /// server side of handshake negotiation
+  seastar::future<stop_t> repeat_handle_connect();
+  seastar::future<stop_t> handle_connect_with_existing(SocketConnectionRef existing,
+                                                        bufferlist&& authorizer_reply);
+  seastar::future<stop_t> replace_existing(SocketConnectionRef existing,
+                                            bufferlist&& authorizer_reply,
+                                            bool is_reset_from_peer = false);
+  seastar::future<stop_t> send_connect_reply(ceph::net::msgr_tag_t tag,
+                                              bufferlist&& authorizer_reply = {});
+  seastar::future<stop_t> send_connect_reply_ready(ceph::net::msgr_tag_t tag,
+                                                    bufferlist&& authorizer_reply);
+
+  seastar::future<> handle_keepalive2();
+  seastar::future<> handle_keepalive2_ack();
+
+  bool require_auth_feature() const;
+  uint32_t get_proto_version(entity_type_t peer_type, bool connec) const;
+  /// client side of handshake negotiation
+  seastar::future<stop_t> repeat_connect();
+  seastar::future<stop_t> handle_connect_reply(ceph::net::msgr_tag_t tag);
+  void reset_session();
+
+  /// state for an incoming message
+  struct MessageReader {
+    ceph_msg_header header;
+    ceph_msg_footer footer;
+    bufferlist front;
+    bufferlist middle;
+    bufferlist data;
+  } m;
+
+  seastar::future<> maybe_throttle();
+  seastar::future<> handle_tags();
+  seastar::future<> handle_ack();
+
+  /// becomes available when handshake completes, and when all previous messages
+  /// have been sent to the output stream. send() chains new messages as
+  /// continuations to this future to act as a queue
+  seastar::future<> send_ready;
+
+  /// encode/write a message
+  seastar::future<> write_message(MessageRef msg);
+
+  ceph::net::Policy<ceph::thread::Throttle> policy;
+  uint64_t features;
+  void set_features(uint64_t new_features) {
+    features = new_features;
+  }
+
+  /// the seq num of the last transmitted message
+  seq_num_t out_seq = 0;
+  /// the seq num of the last received message
+  seq_num_t in_seq = 0;
+  /// update the seq num of last received message
+  /// @returns true if the @c seq is valid, and @c in_seq is updated,
+  ///          false otherwise.
+  bool update_rx_seq(seq_num_t seq);
+
+  seastar::future<> read_message();
+
+  std::unique_ptr<AuthSessionHandler> session_security;
+
+  // messages to be resent after connection gets reset
+  std::queue<MessageRef> out_q;
+  // messages sent, but not yet acked by peer
+  std::queue<MessageRef> sent;
+  static void discard_up_to(std::queue<MessageRef>*, seq_num_t);
+
+  struct Keepalive {
+    struct {
+      const char tag = CEPH_MSGR_TAG_KEEPALIVE2;
+      ceph_timespec stamp;
+    } __attribute__((packed)) req;
+    struct {
+      const char tag = CEPH_MSGR_TAG_KEEPALIVE2_ACK;
+      ceph_timespec stamp;
+    } __attribute__((packed)) ack;
+    ceph_timespec ack_stamp;
+  } k;
+
+  seastar::future<> fault();
+
+  void execute_open();
+
+  seastar::future<> do_send(MessageRef msg);
+  seastar::future<> do_keepalive();
+  seastar::future<> do_close();
+
+ public:
+  SocketConnection(SocketMessenger& messenger,
+                   Dispatcher& dispatcher);
+  ~SocketConnection();
+
+  Messenger* get_messenger() const override;
+
+  int get_peer_type() const override {
+    return peer_type;
+  }
+
+  seastar::future<bool> is_connected() override;
+
+  seastar::future<> send(MessageRef msg) override;
+
+  seastar::future<> keepalive() override;
+
+  seastar::future<> close() override;
+
+  seastar::shard_id shard_id() const override;
+
+  void print(ostream& out) const override;
+
+ public:
+  /// start a handshake from the client's perspective,
+  /// only call when SocketConnection first construct
+  void start_connect(const entity_addr_t& peer_addr,
+                     const entity_type_t& peer_type);
+  /// start a handshake from the server's perspective,
+  /// only call when SocketConnection first construct
+  void start_accept(seastar::foreign_ptr<std::unique_ptr<Socket>>&& socket,
+                    const entity_addr_t& peer_addr);
+
+  /// the number of connections initiated in this session, increment when a
+  /// new connection is established
+  uint32_t connect_seq() const {
+    return h.connect_seq;
+  }
+
+  /// the client side should connect us with a gseq. it will be reset with
+  /// the one of exsting connection if it's greater.
+  uint32_t peer_global_seq() const {
+    return h.peer_global_seq;
+  }
+  seq_num_t rx_seq_num() const {
+    return in_seq;
+  }
+
+  /// current state of connection
+  state_t get_state() const {
+    return state;
+  }
+  bool is_server_side() const {
+    return policy.server;
+  }
+  bool is_lossy() const {
+    return policy.lossy;
+  }
+
+  /// move all messages in the sent list back into the queue
+  void requeue_sent();
+
+  std::tuple<seq_num_t, std::queue<MessageRef>> get_out_queue() {
+    return {out_seq, std::move(out_q)};
+  }
+};
+
+} // namespace ceph::net
diff --git a/src/crimson/net/SocketMessenger.cc b/src/crimson/net/SocketMessenger.cc
new file mode 100644
index 00000000..46a38ff7
--- /dev/null
+++ b/src/crimson/net/SocketMessenger.cc
@@ -0,0 +1,283 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+/*
+ * Ceph - scalable distributed file system
+ *
+ * Copyright (C) 2017 Red Hat, Inc
+ *
+ * This is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License version 2.1, as published by the Free Software
+ * Foundation.  See file COPYING.
+ *
+ */
+
+#include "SocketMessenger.h"
+
+#include <tuple>
+#include <boost/functional/hash.hpp>
+
+#include "auth/Auth.h"
+#include "Errors.h"
+#include "Dispatcher.h"
+#include "Socket.h"
+
+using namespace ceph::net;
+
+namespace {
+  seastar::logger& logger() {
+    return ceph::get_logger(ceph_subsys_ms);
+  }
+}
+
+SocketMessenger::SocketMessenger(const entity_name_t& myname,
+                                 const std::string& logic_name,
+                                 uint32_t nonce,
+                                 int master_sid)
+  : Messenger{myname},
+    master_sid{master_sid},
+    sid{seastar::engine().cpu_id()},
+    logic_name{logic_name},
+    nonce{nonce}
+{}
+
+seastar::future<> SocketMessenger::set_myaddrs(const entity_addrvec_t& addrs)
+{
+  auto my_addrs = addrs;
+  for (auto& addr : my_addrs.v) {
+    addr.nonce = nonce;
+  }
+  return container().invoke_on_all([my_addrs](auto& msgr) {
+      return msgr.Messenger::set_myaddrs(my_addrs);
+    });
+}
+
+seastar::future<> SocketMessenger::bind(const entity_addrvec_t& addrs)
+{
+  ceph_assert(addrs.legacy_addr().get_family() == AF_INET);
+  auto my_addrs = addrs;
+  for (auto& addr : my_addrs.v) {
+    addr.nonce = nonce;
+  }
+  logger().info("listening on {}", my_addrs.legacy_addr().in4_addr());
+  return container().invoke_on_all([my_addrs](auto& msgr) {
+      msgr.do_bind(my_addrs);
+    });
+}
+
+seastar::future<>
+SocketMessenger::try_bind(const entity_addrvec_t& addrs,
+                          uint32_t min_port, uint32_t max_port)
+{
+  auto addr = addrs.legacy_or_front_addr();
+  if (addr.get_port() != 0) {
+    return bind(addrs);
+  }
+  ceph_assert(min_port <= max_port);
+  return seastar::do_with(uint32_t(min_port),
+    [this, max_port, addr] (auto& port) {
+      return seastar::repeat([this, max_port, addr, &port] {
+          auto to_bind = addr;
+          to_bind.set_port(port);
+          return bind(entity_addrvec_t{to_bind})
+            .then([this] {
+              logger().info("{}: try_bind: done", *this);
+              return stop_t::yes;
+            }).handle_exception_type([this, max_port, &port] (const std::system_error& e) {
+              logger().debug("{}: try_bind: {} already used", *this, port);
+              if (port == max_port) {
+                throw e;
+              }
+              ++port;
+              return stop_t::no;
+            });
+        });
+    });
+}
+
+seastar::future<> SocketMessenger::start(Dispatcher *disp) {
+  return container().invoke_on_all([disp](auto& msgr) {
+      return msgr.do_start(disp->get_local_shard());
+    });
+}
+
+seastar::future<ceph::net::ConnectionXRef>
+SocketMessenger::connect(const entity_addr_t& peer_addr, const entity_type_t& peer_type)
+{
+  auto shard = locate_shard(peer_addr);
+  return container().invoke_on(shard, [peer_addr, peer_type](auto& msgr) {
+      return msgr.do_connect(peer_addr, peer_type);
+    }).then([](seastar::foreign_ptr<ConnectionRef>&& conn) {
+      return seastar::make_lw_shared<seastar::foreign_ptr<ConnectionRef>>(std::move(conn));
+    });
+}
+
+seastar::future<> SocketMessenger::shutdown()
+{
+  return container().invoke_on_all([](auto& msgr) {
+      return msgr.do_shutdown();
+    }).finally([this] {
+      return container().invoke_on_all([](auto& msgr) {
+          msgr.shutdown_promise.set_value();
+        });
+    });
+}
+
+void SocketMessenger::do_bind(const entity_addrvec_t& addrs)
+{
+  Messenger::set_myaddrs(addrs);
+
+  // TODO: v2: listen on multiple addresses
+  seastar::socket_address address(addrs.legacy_addr().in4_addr());
+  seastar::listen_options lo;
+  lo.reuse_address = true;
+  listener = seastar::listen(address, lo);
+}
+
+seastar::future<> SocketMessenger::do_start(Dispatcher *disp)
+{
+  dispatcher = disp;
+
+  // start listening if bind() was called
+  if (listener) {
+    seastar::keep_doing([this] {
+        return listener->accept()
+          .then([this] (seastar::connected_socket socket,
+                        seastar::socket_address paddr) {
+            // allocate the connection
+            entity_addr_t peer_addr;
+            peer_addr.set_sockaddr(&paddr.as_posix_sockaddr());
+            auto shard = locate_shard(peer_addr);
+#warning fixme
+            // we currently do dangerous i/o from a Connection core, different from the Socket core.
+            auto sock = seastar::make_foreign(std::make_unique<Socket>(std::move(socket)));
+            // don't wait before accepting another
+            container().invoke_on(shard, [sock = std::move(sock), peer_addr, this](auto& msgr) mutable {
+                SocketConnectionRef conn = seastar::make_shared<SocketConnection>(msgr, *msgr.dispatcher);
+                conn->start_accept(std::move(sock), peer_addr);
+              });
+          });
+      }).handle_exception_type([this] (const std::system_error& e) {
+        // stop gracefully on connection_aborted
+        if (e.code() != error::connection_aborted) {
+          logger().error("{} unexpected error during accept: {}", *this, e);
+        }
+      });
+  }
+
+  return seastar::now();
+}
+
+seastar::foreign_ptr<ceph::net::ConnectionRef>
+SocketMessenger::do_connect(const entity_addr_t& peer_addr, const entity_type_t& peer_type)
+{
+  if (auto found = lookup_conn(peer_addr); found) {
+    return seastar::make_foreign(found->shared_from_this());
+  }
+  SocketConnectionRef conn = seastar::make_shared<SocketConnection>(*this, *dispatcher);
+  conn->start_connect(peer_addr, peer_type);
+  return seastar::make_foreign(conn->shared_from_this());
+}
+
+seastar::future<> SocketMessenger::do_shutdown()
+{
+  if (listener) {
+    listener->abort_accept();
+  }
+  // close all connections
+  return seastar::parallel_for_each(accepting_conns, [] (auto conn) {
+      return conn->close();
+    }).then([this] {
+      ceph_assert(accepting_conns.empty());
+      return seastar::parallel_for_each(connections, [] (auto conn) {
+          return conn.second->close();
+        });
+    }).finally([this] {
+      ceph_assert(connections.empty());
+    });
+}
+
+seastar::future<> SocketMessenger::learned_addr(const entity_addr_t &peer_addr_for_me)
+{
+  if (!get_myaddr().is_blank_ip()) {
+    // already learned or binded
+    return seastar::now();
+  }
+
+  // Only learn IP address if blank.
+  entity_addr_t addr = get_myaddr();
+  addr.u = peer_addr_for_me.u;
+  addr.set_type(peer_addr_for_me.get_type());
+  addr.set_port(get_myaddr().get_port());
+  return set_myaddrs(entity_addrvec_t{addr});
+}
+
+void SocketMessenger::set_default_policy(const SocketPolicy& p)
+{
+  policy_set.set_default(p);
+}
+
+void SocketMessenger::set_policy(entity_type_t peer_type,
+				 const SocketPolicy& p)
+{
+  policy_set.set(peer_type, p);
+}
+
+void SocketMessenger::set_policy_throttler(entity_type_t peer_type,
+					   Throttle* throttle)
+{
+  // only byte throttler is used in OSD
+  policy_set.set_throttlers(peer_type, throttle, nullptr);
+}
+
+seastar::shard_id SocketMessenger::locate_shard(const entity_addr_t& addr)
+{
+  ceph_assert(addr.get_family() == AF_INET);
+  if (master_sid >= 0) {
+    return master_sid;
+  }
+  std::size_t seed = 0;
+  boost::hash_combine(seed, addr.u.sin.sin_addr.s_addr);
+  //boost::hash_combine(seed, addr.u.sin.sin_port);
+  //boost::hash_combine(seed, addr.nonce);
+  return seed % seastar::smp::count;
+}
+
+ceph::net::SocketConnectionRef SocketMessenger::lookup_conn(const entity_addr_t& addr)
+{
+  if (auto found = connections.find(addr);
+      found != connections.end()) {
+    return found->second;
+  } else {
+    return nullptr;
+  }
+}
+
+void SocketMessenger::accept_conn(SocketConnectionRef conn)
+{
+  accepting_conns.insert(conn);
+}
+
+void SocketMessenger::unaccept_conn(SocketConnectionRef conn)
+{
+  accepting_conns.erase(conn);
+}
+
+void SocketMessenger::register_conn(SocketConnectionRef conn)
+{
+  if (master_sid >= 0) {
+    ceph_assert(static_cast<int>(sid) == master_sid);
+  }
+  auto [i, added] = connections.emplace(conn->get_peer_addr(), conn);
+  std::ignore = i;
+  ceph_assert(added);
+}
+
+void SocketMessenger::unregister_conn(SocketConnectionRef conn)
+{
+  ceph_assert(conn);
+  auto found = connections.find(conn->get_peer_addr());
+  ceph_assert(found != connections.end());
+  ceph_assert(found->second == conn);
+  connections.erase(found);
+}
diff --git a/src/crimson/net/SocketMessenger.h b/src/crimson/net/SocketMessenger.h
new file mode 100644
index 00000000..535dea3a
--- /dev/null
+++ b/src/crimson/net/SocketMessenger.h
@@ -0,0 +1,119 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+/*
+ * Ceph - scalable distributed file system
+ *
+ * Copyright (C) 2017 Red Hat, Inc
+ *
+ * This is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License version 2.1, as published by the Free Software
+ * Foundation.  See file COPYING.
+ *
+ */
+
+#pragma once
+
+#include <map>
+#include <optional>
+#include <set>
+#include <seastar/core/gate.hh>
+#include <seastar/core/reactor.hh>
+#include <seastar/core/sharded.hh>
+
+#include "Messenger.h"
+#include "SocketConnection.h"
+
+namespace ceph::net {
+
+class SocketMessenger final : public Messenger, public seastar::peering_sharded_service<SocketMessenger> {
+  const int master_sid;
+  const seastar::shard_id sid;
+  seastar::promise<> shutdown_promise;
+
+  std::optional<seastar::server_socket> listener;
+  Dispatcher *dispatcher = nullptr;
+  std::map<entity_addr_t, SocketConnectionRef> connections;
+  std::set<SocketConnectionRef> accepting_conns;
+  ceph::net::PolicySet<Throttle> policy_set;
+  // Distinguish messengers with meaningful names for debugging
+  const std::string logic_name;
+  const uint32_t nonce;
+
+  seastar::future<> accept(seastar::connected_socket socket,
+                           seastar::socket_address paddr);
+
+  void do_bind(const entity_addrvec_t& addr);
+  seastar::future<> do_start(Dispatcher *disp);
+  seastar::foreign_ptr<ConnectionRef> do_connect(const entity_addr_t& peer_addr,
+                                                 const entity_type_t& peer_type);
+  seastar::future<> do_shutdown();
+  // conn sharding options:
+  // 0. Compatible (master_sid >= 0): place all connections to one master shard
+  // 1. Simplest (master_sid < 0): sharded by ip only
+  // 2. Balanced (not implemented): sharded by ip + port + nonce,
+  //        but, need to move SocketConnection between cores.
+  seastar::shard_id locate_shard(const entity_addr_t& addr);
+
+ public:
+  SocketMessenger(const entity_name_t& myname,
+                  const std::string& logic_name,
+                  uint32_t nonce,
+                  int master_sid);
+
+  seastar::future<> set_myaddrs(const entity_addrvec_t& addr) override;
+
+  // Messenger interfaces are assumed to be called from its own shard, but its
+  // behavior should be symmetric when called from any shard.
+  seastar::future<> bind(const entity_addrvec_t& addr) override;
+
+  seastar::future<> try_bind(const entity_addrvec_t& addr,
+                             uint32_t min_port, uint32_t max_port) override;
+
+  seastar::future<> start(Dispatcher *dispatcher) override;
+
+  seastar::future<ConnectionXRef> connect(const entity_addr_t& peer_addr,
+                                          const entity_type_t& peer_type) override;
+  // can only wait once
+  seastar::future<> wait() override {
+    return shutdown_promise.get_future();
+  }
+
+  seastar::future<> shutdown() override;
+
+  Messenger* get_local_shard() override {
+    return &container().local();
+  }
+
+  void print(ostream& out) const override {
+    out << get_myname()
+        << "(" << logic_name
+        << ") " << get_myaddr();
+  }
+
+  void set_default_policy(const SocketPolicy& p) override;
+
+  void set_policy(entity_type_t peer_type, const SocketPolicy& p) override;
+
+  void set_policy_throttler(entity_type_t peer_type, Throttle* throttle) override;
+
+ public:
+  seastar::future<> learned_addr(const entity_addr_t &peer_addr_for_me);
+
+  SocketConnectionRef lookup_conn(const entity_addr_t& addr);
+  void accept_conn(SocketConnectionRef);
+  void unaccept_conn(SocketConnectionRef);
+  void register_conn(SocketConnectionRef);
+  void unregister_conn(SocketConnectionRef);
+
+  // required by sharded<>
+  seastar::future<> stop() {
+    return seastar::make_ready_future<>();
+  }
+
+  seastar::shard_id shard_id() const {
+    return sid;
+  }
+};
+
+} // namespace ceph::net
diff --git a/src/crimson/os/CMakeLists.txt b/src/crimson/os/CMakeLists.txt
new file mode 100644
index 00000000..264e3525
--- /dev/null
+++ b/src/crimson/os/CMakeLists.txt
@@ -0,0 +1,7 @@
+add_library(crimson-os
+  cyan_store.cc
+  cyan_collection.cc
+  cyan_object.cc
+  Transaction.cc)
+target_link_libraries(crimson-os
+  crimson)
diff --git a/src/crimson/os/Transaction.cc b/src/crimson/os/Transaction.cc
new file mode 100644
index 00000000..acf99c59
--- /dev/null
+++ b/src/crimson/os/Transaction.cc
@@ -0,0 +1,507 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+
+#include "Transaction.h"
+#include "include/denc.h"
+
+namespace ceph::os
+{
+
+void Transaction::iterator::decode_attrset_bl(bufferlist *pbl)
+{
+  using ceph::decode;
+  auto start = data_bl_p;
+  __u32 n;
+  decode(n, data_bl_p);
+  unsigned len = 4;
+  while (n--) {
+    __u32 l;
+    decode(l, data_bl_p);
+    data_bl_p.advance(l);
+    len += 4 + l;
+    decode(l, data_bl_p);
+    data_bl_p.advance(l);
+    len += 4 + l;
+  }
+  start.copy(len, *pbl);  
+}
+
+void Transaction::iterator::decode_keyset_bl(bufferlist *pbl)
+{
+  using ceph::decode;
+  auto start = data_bl_p;
+  __u32 n;
+  decode(n, data_bl_p);
+  unsigned len = 4;
+  while (n--) {
+    __u32 l;
+    decode(l, data_bl_p);
+    data_bl_p.advance(l);
+    len += 4 + l;
+  }
+  start.copy(len, *pbl);
+}
+
+void Transaction::dump(ceph::Formatter *f)
+{
+  f->open_array_section("ops");
+  iterator i = begin();
+  int op_num = 0;
+  bool stop_looping = false;
+  while (i.have_op() && !stop_looping) {
+    Transaction::Op *op = i.decode_op();
+    f->open_object_section("op");
+    f->dump_int("op_num", op_num);
+    
+    switch (op->op) {
+    case Transaction::OP_NOP:
+      f->dump_string("op_name", "nop");
+      break;
+    case Transaction::OP_TOUCH:
+      {
+        coll_t cid = i.get_cid(op->cid);
+        ghobject_t oid = i.get_oid(op->oid);
+        f->dump_string("op_name", "touch");
+        f->dump_stream("collection") << cid;
+        f->dump_stream("oid") << oid;
+      }
+      break;
+      
+    case Transaction::OP_WRITE:
+      {
+        coll_t cid = i.get_cid(op->cid);
+        ghobject_t oid = i.get_oid(op->oid);
+        uint64_t off = op->off;
+        uint64_t len = op->len;
+        bufferlist bl;
+        i.decode_bl(bl);
+        f->dump_string("op_name", "write");
+        f->dump_stream("collection") << cid;
+        f->dump_stream("oid") << oid;
+        f->dump_unsigned("length", len);
+        f->dump_unsigned("offset", off);
+        f->dump_unsigned("bufferlist length", bl.length());
+      }
+      break;
+      
+    case Transaction::OP_ZERO:
+      {
+        coll_t cid = i.get_cid(op->cid);
+        ghobject_t oid = i.get_oid(op->oid);
+        uint64_t off = op->off;
+        uint64_t len = op->len;
+        f->dump_string("op_name", "zero");
+        f->dump_stream("collection") << cid;
+        f->dump_stream("oid") << oid;
+        f->dump_unsigned("offset", off);
+        f->dump_unsigned("length", len);
+      }
+      break;
+      
+    case Transaction::OP_TRIMCACHE:
+      {
+        // deprecated, no-op
+        f->dump_string("op_name", "trim_cache");
+      }
+      break;
+      
+    case Transaction::OP_TRUNCATE:
+      {
+        coll_t cid = i.get_cid(op->cid);
+        ghobject_t oid = i.get_oid(op->oid);
+        uint64_t off = op->off;
+        f->dump_string("op_name", "truncate");
+        f->dump_stream("collection") << cid;
+        f->dump_stream("oid") << oid;
+        f->dump_unsigned("offset", off);
+      }
+      break;
+      
+    case Transaction::OP_REMOVE:
+      {
+        coll_t cid = i.get_cid(op->cid);
+        ghobject_t oid = i.get_oid(op->oid);
+        f->dump_string("op_name", "remove");
+        f->dump_stream("collection") << cid;
+        f->dump_stream("oid") << oid;
+      }
+      break;
+      
+    case Transaction::OP_SETATTR:
+      {
+        coll_t cid = i.get_cid(op->cid);
+        ghobject_t oid = i.get_oid(op->oid);
+        string name = i.decode_string();
+        bufferlist bl;
+        i.decode_bl(bl);
+        f->dump_string("op_name", "setattr");
+        f->dump_stream("collection") << cid;
+        f->dump_stream("oid") << oid;
+        f->dump_string("name", name);
+        f->dump_unsigned("length", bl.length());
+      }
+      break;
+      
+    case Transaction::OP_SETATTRS:
+      {
+        coll_t cid = i.get_cid(op->cid);
+        ghobject_t oid = i.get_oid(op->oid);
+        map<string, bufferptr> aset;
+        i.decode_attrset(aset);
+        f->dump_string("op_name", "setattrs");
+        f->dump_stream("collection") << cid;
+        f->dump_stream("oid") << oid;
+        f->open_object_section("attr_lens");
+        for (map<string,bufferptr>::iterator p = aset.begin();
+	    p != aset.end(); ++p) {
+          f->dump_unsigned(p->first.c_str(), p->second.length());
+        }
+        f->close_section();
+      }
+      break;
+
+    case Transaction::OP_RMATTR:
+      {
+        coll_t cid = i.get_cid(op->cid);
+        ghobject_t oid = i.get_oid(op->oid);
+        string name = i.decode_string();
+        f->dump_string("op_name", "rmattr");
+        f->dump_stream("collection") << cid;
+        f->dump_stream("oid") << oid;
+        f->dump_string("name", name);
+      }
+      break;
+
+    case Transaction::OP_RMATTRS:
+      {
+        coll_t cid = i.get_cid(op->cid);
+        ghobject_t oid = i.get_oid(op->oid);
+        f->dump_string("op_name", "rmattrs");
+        f->dump_stream("collection") << cid;
+        f->dump_stream("oid") << oid;
+      }
+      break;
+      
+    case Transaction::OP_CLONE:
+      {
+        coll_t cid = i.get_cid(op->cid);
+        ghobject_t oid = i.get_oid(op->oid);
+        ghobject_t noid = i.get_oid(op->dest_oid);
+        f->dump_string("op_name", "clone");
+        f->dump_stream("collection") << cid;
+        f->dump_stream("src_oid") << oid;
+        f->dump_stream("dst_oid") << noid;
+      }
+      break;
+
+    case Transaction::OP_CLONERANGE:
+      {
+        coll_t cid = i.get_cid(op->cid);
+        ghobject_t oid = i.get_oid(op->oid);
+        ghobject_t noid = i.get_oid(op->dest_oid);
+        uint64_t off = op->off;
+        uint64_t len = op->len;
+        f->dump_string("op_name", "clonerange");
+        f->dump_stream("collection") << cid;
+        f->dump_stream("src_oid") << oid;
+        f->dump_stream("dst_oid") << noid;
+        f->dump_unsigned("offset", off);
+        f->dump_unsigned("len", len);
+      }
+      break;
+
+    case Transaction::OP_CLONERANGE2:
+      {
+        coll_t cid = i.get_cid(op->cid);
+        ghobject_t oid = i.get_oid(op->oid);
+        ghobject_t noid = i.get_oid(op->dest_oid);
+        uint64_t srcoff = op->off;
+        uint64_t len = op->len;
+        uint64_t dstoff = op->dest_off;
+        f->dump_string("op_name", "clonerange2");
+        f->dump_stream("collection") << cid;
+        f->dump_stream("src_oid") << oid;
+        f->dump_stream("dst_oid") << noid;
+        f->dump_unsigned("src_offset", srcoff);
+        f->dump_unsigned("len", len);
+        f->dump_unsigned("dst_offset", dstoff);
+      }
+      break;
+
+    case Transaction::OP_MKCOLL:
+      {
+        coll_t cid = i.get_cid(op->cid);
+        f->dump_string("op_name", "mkcoll");
+        f->dump_stream("collection") << cid;
+      }
+      break;
+
+    case Transaction::OP_COLL_HINT:
+      {
+	using ceph::decode;
+        coll_t cid = i.get_cid(op->cid);
+        uint32_t type = op->hint_type;
+        f->dump_string("op_name", "coll_hint");
+        f->dump_stream("collection") << cid;
+        f->dump_unsigned("type", type);
+        bufferlist hint;
+        i.decode_bl(hint);
+        auto hiter = hint.cbegin();
+        if (type == Transaction::COLL_HINT_EXPECTED_NUM_OBJECTS) {
+          uint32_t pg_num;
+          uint64_t num_objs;
+          decode(pg_num, hiter);
+          decode(num_objs, hiter);
+          f->dump_unsigned("pg_num", pg_num);
+          f->dump_unsigned("expected_num_objects", num_objs);
+        }
+      }
+      break;
+
+    case Transaction::OP_COLL_SET_BITS:
+      {
+        coll_t cid = i.get_cid(op->cid);
+        f->dump_string("op_name", "coll_set_bits");
+        f->dump_stream("collection") << cid;
+        f->dump_unsigned("bits", op->split_bits);
+      }
+      break;
+
+    case Transaction::OP_RMCOLL:
+      {
+        coll_t cid = i.get_cid(op->cid);
+        f->dump_string("op_name", "rmcoll");
+        f->dump_stream("collection") << cid;
+      }
+      break;
+
+    case Transaction::OP_COLL_ADD:
+      {
+        coll_t ocid = i.get_cid(op->cid);
+        coll_t ncid = i.get_cid(op->dest_cid);
+        ghobject_t oid = i.get_oid(op->oid);
+        f->dump_string("op_name", "collection_add");
+        f->dump_stream("src_collection") << ocid;
+        f->dump_stream("dst_collection") << ncid;
+        f->dump_stream("oid") << oid;
+      }
+      break;
+
+    case Transaction::OP_COLL_REMOVE:
+       {
+        coll_t cid = i.get_cid(op->cid);
+        ghobject_t oid = i.get_oid(op->oid);
+        f->dump_string("op_name", "collection_remove");
+        f->dump_stream("collection") << cid;
+        f->dump_stream("oid") << oid;
+       }
+      break;
+
+    case Transaction::OP_COLL_MOVE:
+       {
+        coll_t ocid = i.get_cid(op->cid);
+        coll_t ncid = i.get_cid(op->dest_cid);
+        ghobject_t oid = i.get_oid(op->oid);
+        f->open_object_section("collection_move");
+        f->dump_stream("src_collection") << ocid;
+        f->dump_stream("dst_collection") << ncid;
+        f->dump_stream("oid") << oid;
+        f->close_section();
+       }
+      break;
+
+    case Transaction::OP_COLL_SETATTR:
+      {
+        coll_t cid = i.get_cid(op->cid);
+        string name = i.decode_string();
+        bufferlist bl;
+        i.decode_bl(bl);
+        f->dump_string("op_name", "collection_setattr");
+        f->dump_stream("collection") << cid;
+        f->dump_string("name", name);
+        f->dump_unsigned("length", bl.length());
+      }
+      break;
+
+    case Transaction::OP_COLL_RMATTR:
+      {
+        coll_t cid = i.get_cid(op->cid);
+        string name = i.decode_string();
+        f->dump_string("op_name", "collection_rmattr");
+        f->dump_stream("collection") << cid;
+        f->dump_string("name", name);
+      }
+      break;
+
+    case Transaction::OP_COLL_RENAME:
+      {
+        f->dump_string("op_name", "collection_rename");
+      }
+      break;
+
+    case Transaction::OP_OMAP_CLEAR:
+      {
+        coll_t cid = i.get_cid(op->cid);
+        ghobject_t oid = i.get_oid(op->oid);
+        f->dump_string("op_name", "omap_clear");
+        f->dump_stream("collection") << cid;
+        f->dump_stream("oid") << oid;
+      }
+      break;
+
+    case Transaction::OP_OMAP_SETKEYS:
+      {
+        coll_t cid = i.get_cid(op->cid);
+        ghobject_t oid = i.get_oid(op->oid);
+        map<string, bufferlist> aset;
+        i.decode_attrset(aset);
+        f->dump_string("op_name", "omap_setkeys");
+        f->dump_stream("collection") << cid;
+        f->dump_stream("oid") << oid;
+        f->open_object_section("attr_lens");
+        for (map<string, bufferlist>::iterator p = aset.begin();
+             p != aset.end(); ++p) {
+          f->dump_unsigned(p->first.c_str(), p->second.length());
+        }
+        f->close_section();
+      }
+      break;
+
+    case Transaction::OP_OMAP_RMKEYS:
+      {
+        coll_t cid = i.get_cid(op->cid);
+        ghobject_t oid = i.get_oid(op->oid);
+        set<string> keys;
+        i.decode_keyset(keys);
+        f->dump_string("op_name", "omap_rmkeys");
+        f->dump_stream("collection") << cid;
+        f->dump_stream("oid") << oid;
+        f->open_array_section("attrs");
+        for (auto& k : keys) {
+          f->dump_string("", k.c_str());
+        }
+        f->close_section();
+      }
+      break;
+
+    case Transaction::OP_OMAP_SETHEADER:
+      {
+        coll_t cid = i.get_cid(op->cid);
+        ghobject_t oid = i.get_oid(op->oid);
+        bufferlist bl;
+        i.decode_bl(bl);
+        f->dump_string("op_name", "omap_setheader");
+        f->dump_stream("collection") << cid;
+        f->dump_stream("oid") << oid;
+        f->dump_stream("header_length") << bl.length();
+      }
+      break;
+
+    case Transaction::OP_SPLIT_COLLECTION:
+      {
+        coll_t cid = i.get_cid(op->cid);
+        uint32_t bits = op->split_bits;
+        uint32_t rem = op->split_rem;
+        coll_t dest = i.get_cid(op->dest_cid);
+        f->dump_string("op_name", "op_split_collection_create");
+        f->dump_stream("collection") << cid;
+        f->dump_stream("bits") << bits;
+        f->dump_stream("rem") << rem;
+        f->dump_stream("dest") << dest;
+      }
+      break;
+
+    case Transaction::OP_SPLIT_COLLECTION2:
+      {
+        coll_t cid = i.get_cid(op->cid);
+        uint32_t bits = op->split_bits;
+        uint32_t rem = op->split_rem;
+        coll_t dest = i.get_cid(op->dest_cid);
+        f->dump_string("op_name", "op_split_collection");
+        f->dump_stream("collection") << cid;
+        f->dump_stream("bits") << bits;
+        f->dump_stream("rem") << rem;
+        f->dump_stream("dest") << dest;
+      }
+      break;
+
+    case Transaction::OP_MERGE_COLLECTION:
+      {
+        coll_t cid = i.get_cid(op->cid);
+        uint32_t bits = op->split_bits;
+        coll_t dest = i.get_cid(op->dest_cid);
+        f->dump_string("op_name", "op_merge_collection");
+        f->dump_stream("collection") << cid;
+        f->dump_stream("dest") << dest;
+        f->dump_stream("bits") << bits;
+      }
+      break;
+
+    case Transaction::OP_OMAP_RMKEYRANGE:
+      {
+        coll_t cid = i.get_cid(op->cid);
+        ghobject_t oid = i.get_oid(op->oid);
+        string first, last;
+        first = i.decode_string();
+        last = i.decode_string();
+        f->dump_string("op_name", "op_omap_rmkeyrange");
+        f->dump_stream("collection") << cid;
+        f->dump_stream("oid") << oid;
+        f->dump_string("first", first);
+        f->dump_string("last", last);
+      }
+      break;
+
+    case Transaction::OP_COLL_MOVE_RENAME:
+      {
+        coll_t old_cid = i.get_cid(op->cid);
+        ghobject_t old_oid = i.get_oid(op->oid);
+        coll_t new_cid = i.get_cid(op->dest_cid);
+        ghobject_t new_oid = i.get_oid(op->dest_oid);
+        f->dump_string("op_name", "op_coll_move_rename");
+        f->dump_stream("old_collection") << old_cid;
+        f->dump_stream("old_oid") << old_oid;
+        f->dump_stream("new_collection") << new_cid;
+        f->dump_stream("new_oid") << new_oid;
+      }
+      break;
+
+    case Transaction::OP_TRY_RENAME:
+      {
+        coll_t cid = i.get_cid(op->cid);
+        ghobject_t old_oid = i.get_oid(op->oid);
+        ghobject_t new_oid = i.get_oid(op->dest_oid);
+        f->dump_string("op_name", "op_coll_move_rename");
+        f->dump_stream("collection") << cid;
+        f->dump_stream("old_oid") << old_oid;
+        f->dump_stream("new_oid") << new_oid;
+      }
+      break;
+	
+    case Transaction::OP_SETALLOCHINT:
+      {
+        coll_t cid = i.get_cid(op->cid);
+        ghobject_t oid = i.get_oid(op->oid);
+        uint64_t expected_object_size = op->expected_object_size;
+        uint64_t expected_write_size = op->expected_write_size;
+        f->dump_string("op_name", "op_setallochint");
+        f->dump_stream("collection") << cid;
+        f->dump_stream("oid") << oid;
+        f->dump_stream("expected_object_size") << expected_object_size;
+        f->dump_stream("expected_write_size") << expected_write_size;
+      }
+      break;
+
+    default:
+      f->dump_string("op_name", "unknown");
+      f->dump_unsigned("op_code", op->op);
+      stop_looping = true;
+      break;
+    }
+    f->close_section();
+    op_num++;
+  }
+  f->close_section();
+}
+
+}
diff --git a/src/crimson/os/Transaction.h b/src/crimson/os/Transaction.h
new file mode 100644
index 00000000..c6f660fe
--- /dev/null
+++ b/src/crimson/os/Transaction.h
@@ -0,0 +1,1234 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*- 
+// vim: ts=8 sw=2 smarttab
+
+#include <map>
+
+#include "include/int_types.h"
+#include "include/buffer.h"
+#include "osd/osd_types.h"
+
+/*********************************
+ * transaction
+ *
+ * A Transaction represents a sequence of primitive mutation
+ * operations.
+ *
+ * Three events in the life of a Transaction result in
+ * callbacks. Any Transaction can contain any number of callback
+ * objects (Context) for any combination of the three classes of
+ * callbacks:
+ *
+ *    on_applied_sync, on_applied, and on_commit.
+ *
+ * The "on_applied" and "on_applied_sync" callbacks are invoked when
+ * the modifications requested by the Transaction are visible to
+ * subsequent ObjectStore operations, i.e., the results are
+ * readable. The only conceptual difference between on_applied and
+ * on_applied_sync is the specific thread and locking environment in
+ * which the callbacks operate.  "on_applied_sync" is called
+ * directly by an ObjectStore execution thread. It is expected to
+ * execute quickly and must not acquire any locks of the calling
+ * environment. Conversely, "on_applied" is called from the separate
+ * Finisher thread, meaning that it can contend for calling
+ * environment locks. NB, on_applied and on_applied_sync are
+ * sometimes called on_readable and on_readable_sync.
+ *
+ * The "on_commit" callback is also called from the Finisher thread
+ * and indicates that all of the mutations have been durably
+ * committed to stable storage (i.e., are now software/hardware
+ * crashproof).
+ *
+ * At the implementation level, each mutation primitive (and its
+ * associated data) can be serialized to a single buffer.  That
+ * serialization, however, does not copy any data, but (using the
+ * bufferlist library) will reference the original buffers.  This
+ * implies that the buffer that contains the data being submitted
+ * must remain stable until the on_commit callback completes.  In
+ * practice, bufferlist handles all of this for you and this
+ * subtlety is only relevant if you are referencing an existing
+ * buffer via buffer::raw_static.
+ *
+ * Some implementations of ObjectStore choose to implement their own
+ * form of journaling that uses the serialized form of a
+ * Transaction. This requires that the encode/decode logic properly
+ * version itself and handle version upgrades that might change the
+ * format of the encoded Transaction. This has already happened a
+ * couple of times and the Transaction object contains some helper
+ * variables that aid in this legacy decoding:
+ *
+ *   sobject_encoding detects an older/simpler version of oid
+ *   present in pre-bobtail versions of ceph.  use_pool_override
+ *   also detects a situation where the pool of an oid can be
+ *   overridden for legacy operations/buffers.  For non-legacy
+ *   implementations of ObjectStore, neither of these fields are
+ *   relevant.
+ *
+ *
+ * TRANSACTION ISOLATION
+ *
+ * Except as noted above, isolation is the responsibility of the
+ * caller. In other words, if any storage element (storage element
+ * == any of the four portions of an object as described above) is
+ * altered by a transaction (including deletion), the caller
+ * promises not to attempt to read that element while the
+ * transaction is pending (here pending means from the time of
+ * issuance until the "on_applied_sync" callback has been
+ * received). Violations of isolation need not be detected by
+ * ObjectStore and there is no corresponding error mechanism for
+ * reporting an isolation violation (crashing would be the
+ * appropriate way to report an isolation violation if detected).
+ *
+ * Enumeration operations may violate transaction isolation as
+ * described above when a storage element is being created or
+ * deleted as part of a transaction. In this case, ObjectStore is
+ * allowed to consider the enumeration operation to either precede
+ * or follow the violating transaction element. In other words, the
+ * presence/absence of the mutated element in the enumeration is
+ * entirely at the discretion of ObjectStore. The arbitrary ordering
+ * applies independently to each transaction element. For example,
+ * if a transaction contains two mutating elements "create A" and
+ * "delete B". And an enumeration operation is performed while this
+ * transaction is pending. It is permissible for ObjectStore to
+ * report any of the four possible combinations of the existence of
+ * A and B.
+ *
+ */
+namespace ceph::os {
+class Transaction {
+public:
+  enum {
+    OP_NOP =          0,
+    OP_TOUCH =        9,   // cid, oid
+    OP_WRITE =        10,  // cid, oid, offset, len, bl
+    OP_ZERO =         11,  // cid, oid, offset, len
+    OP_TRUNCATE =     12,  // cid, oid, len
+    OP_REMOVE =       13,  // cid, oid
+    OP_SETATTR =      14,  // cid, oid, attrname, bl
+    OP_SETATTRS =     15,  // cid, oid, attrset
+    OP_RMATTR =       16,  // cid, oid, attrname
+    OP_CLONE =        17,  // cid, oid, newoid
+    OP_CLONERANGE =   18,  // cid, oid, newoid, offset, len
+    OP_CLONERANGE2 =  30,  // cid, oid, newoid, srcoff, len, dstoff
+
+    OP_TRIMCACHE =    19,  // cid, oid, offset, len  **DEPRECATED**
+
+    OP_MKCOLL =       20,  // cid
+    OP_RMCOLL =       21,  // cid
+    OP_COLL_ADD =     22,  // cid, oldcid, oid
+    OP_COLL_REMOVE =  23,  // cid, oid
+    OP_COLL_SETATTR = 24,  // cid, attrname, bl
+    OP_COLL_RMATTR =  25,  // cid, attrname
+    OP_COLL_SETATTRS = 26,  // cid, attrset
+    OP_COLL_MOVE =    8,   // newcid, oldcid, oid
+
+    OP_RMATTRS =      28,  // cid, oid
+    OP_COLL_RENAME =       29,  // cid, newcid
+
+    OP_OMAP_CLEAR = 31,   // cid
+    OP_OMAP_SETKEYS = 32, // cid, attrset
+    OP_OMAP_RMKEYS = 33,  // cid, keyset
+    OP_OMAP_SETHEADER = 34, // cid, header
+    OP_SPLIT_COLLECTION = 35, // cid, bits, destination
+    OP_SPLIT_COLLECTION2 = 36, /* cid, bits, destination
+		    doesn't create the destination */
+    OP_OMAP_RMKEYRANGE = 37,  // cid, oid, firstkey, lastkey
+    OP_COLL_MOVE_RENAME = 38,   // oldcid, oldoid, newcid, newoid
+    OP_SETALLOCHINT = 39,  // cid, oid, object_size, write_size
+    OP_COLL_HINT = 40, // cid, type, bl
+
+    OP_TRY_RENAME = 41,   // oldcid, oldoid, newoid
+
+    OP_COLL_SET_BITS = 42, // cid, bits
+
+    OP_MERGE_COLLECTION = 43, // cid, destination
+  };
+
+  // Transaction hint type
+  enum {
+    COLL_HINT_EXPECTED_NUM_OBJECTS = 1,
+  };
+
+  struct Op {
+    ceph_le32 op;
+    ceph_le32 cid;
+    ceph_le32 oid;
+    ceph_le64 off;
+    ceph_le64 len;
+    ceph_le32 dest_cid;
+    ceph_le32 dest_oid;               //OP_CLONE, OP_CLONERANGE
+    ceph_le64 dest_off;               //OP_CLONERANGE
+    union {
+      struct {
+        ceph_le32 hint_type;          //OP_COLL_HINT
+      };
+      struct {
+        ceph_le32 alloc_hint_flags;   //OP_SETALLOCHINT
+      };
+    };
+    ceph_le64 expected_object_size;   //OP_SETALLOCHINT
+    ceph_le64 expected_write_size;    //OP_SETALLOCHINT
+    ceph_le32 split_bits;             //OP_SPLIT_COLLECTION2,OP_COLL_SET_BITS,
+                                      //OP_MKCOLL
+    ceph_le32 split_rem;              //OP_SPLIT_COLLECTION2
+  } __attribute__ ((packed)) ;
+
+  struct TransactionData {
+    ceph_le64 ops;
+    ceph_le32 largest_data_len;
+    ceph_le32 largest_data_off;
+    ceph_le32 largest_data_off_in_data_bl;
+    ceph_le32 fadvise_flags;
+
+    TransactionData() noexcept :
+    ops(init_le64(0)),
+      largest_data_len(init_le32(0)),
+      largest_data_off(init_le32(0)),
+      largest_data_off_in_data_bl(init_le32(0)),
+	fadvise_flags(init_le32(0)) { }
+
+      // override default move operations to reset default values
+    TransactionData(TransactionData&& other) noexcept :
+    ops(other.ops),
+      largest_data_len(other.largest_data_len),
+      largest_data_off(other.largest_data_off),
+      largest_data_off_in_data_bl(other.largest_data_off_in_data_bl),
+      fadvise_flags(other.fadvise_flags) {
+      other.ops = 0;
+      other.largest_data_len = 0;
+      other.largest_data_off = 0;
+      other.largest_data_off_in_data_bl = 0;
+      other.fadvise_flags = 0;
+    }
+    TransactionData& operator=(TransactionData&& other) noexcept {
+      ops = other.ops;
+      largest_data_len = other.largest_data_len;
+      largest_data_off = other.largest_data_off;
+      largest_data_off_in_data_bl = other.largest_data_off_in_data_bl;
+      fadvise_flags = other.fadvise_flags;
+      other.ops = 0;
+      other.largest_data_len = 0;
+      other.largest_data_off = 0;
+      other.largest_data_off_in_data_bl = 0;
+      other.fadvise_flags = 0;
+      return *this;
+    }
+
+    TransactionData(const TransactionData& other) = default;
+    TransactionData& operator=(const TransactionData& other) = default;
+
+    void encode(bufferlist& bl) const {
+      bl.append((char*)this, sizeof(TransactionData));
+    }
+    void decode(bufferlist::const_iterator &bl) {
+      bl.copy(sizeof(TransactionData), (char*)this);
+    }
+  } __attribute__ ((packed)) ;
+
+private:
+  TransactionData data;
+
+  std::map<coll_t, __le32> coll_index;
+  std::map<ghobject_t, __le32> object_index;
+
+  __le32 coll_id {0};
+  __le32 object_id {0};
+
+  bufferlist data_bl;
+  bufferlist op_bl;
+
+  std::list<Context *> on_applied;
+  std::list<Context *> on_commit;
+  std::list<Context *> on_applied_sync;
+
+public:
+  Transaction() = default;
+
+  explicit Transaction(bufferlist::const_iterator &dp) {
+    decode(dp);
+  }
+  explicit Transaction(bufferlist &nbl) {
+    auto dp = nbl.cbegin();
+    decode(dp);
+  }
+
+  // override default move operations to reset default values
+  Transaction(Transaction&& other) noexcept :
+    data(std::move(other.data)),
+    coll_index(std::move(other.coll_index)),
+    object_index(std::move(other.object_index)),
+    coll_id(other.coll_id),
+    object_id(other.object_id),
+    data_bl(std::move(other.data_bl)),
+    op_bl(std::move(other.op_bl)),
+    on_applied(std::move(other.on_applied)),
+    on_commit(std::move(other.on_commit)),
+    on_applied_sync(std::move(other.on_applied_sync)) {
+    other.coll_id = 0;
+    other.object_id = 0;
+  }
+
+  Transaction& operator=(Transaction&& other) noexcept {
+    data = std::move(other.data);
+    coll_index = std::move(other.coll_index);
+    object_index = std::move(other.object_index);
+    coll_id = other.coll_id;
+    object_id = other.object_id;
+    data_bl = std::move(other.data_bl);
+    op_bl = std::move(other.op_bl);
+    on_applied = std::move(other.on_applied);
+    on_commit = std::move(other.on_commit);
+    on_applied_sync = std::move(other.on_applied_sync);
+    other.coll_id = 0;
+    other.object_id = 0;
+    return *this;
+  }
+
+  Transaction(const Transaction& other) = default;
+  Transaction& operator=(const Transaction& other) = default;
+
+  // expose object_index for FileStore::Op's benefit
+  const map<ghobject_t, __le32>& get_object_index() const {
+    return object_index;
+  }
+
+  /* Operations on callback contexts */
+  void register_on_applied(Context *c) {
+    if (!c) return;
+    on_applied.push_back(c);
+  }
+  void register_on_commit(Context *c) {
+    if (!c) return;
+    on_commit.push_back(c);
+  }
+  void register_on_applied_sync(Context *c) {
+    if (!c) return;
+    on_applied_sync.push_back(c);
+  }
+  void register_on_complete(Context *c) {
+    if (!c) return;
+    RunOnDeleteRef _complete (std::make_shared<RunOnDelete>(c));
+    register_on_applied(new ContainerContext<RunOnDeleteRef>(_complete));
+    register_on_commit(new ContainerContext<RunOnDeleteRef>(_complete));
+  }
+  bool has_contexts() const {
+    return
+      !on_commit.empty() ||
+      !on_applied.empty() ||
+      !on_applied_sync.empty();
+  }
+
+  static void collect_contexts(vector<Transaction>& t,
+			       Context **out_on_applied,
+			       Context **out_on_commit,
+			       Context **out_on_applied_sync) {
+    ceph_assert(out_on_applied);
+    ceph_assert(out_on_commit);
+    ceph_assert(out_on_applied_sync);
+    std::list<Context *> on_applied, on_commit, on_applied_sync;
+    for (auto& i : t) {
+      on_applied.splice(on_applied.end(), i.on_applied);
+      on_commit.splice(on_commit.end(), i.on_commit);
+      on_applied_sync.splice(on_applied_sync.end(), i.on_applied_sync);
+    }
+    *out_on_applied = C_Contexts::list_to_context(on_applied);
+    *out_on_commit = C_Contexts::list_to_context(on_commit);
+    *out_on_applied_sync = C_Contexts::list_to_context(on_applied_sync);
+  }
+  static void collect_contexts(vector<Transaction>& t,
+			       std::list<Context*> *out_on_applied,
+			       std::list<Context*> *out_on_commit,
+			       std::list<Context*> *out_on_applied_sync) {
+    ceph_assert(out_on_applied);
+    ceph_assert(out_on_commit);
+    ceph_assert(out_on_applied_sync);
+    for (auto& i : t) {
+      out_on_applied->splice(out_on_applied->end(), i.on_applied);
+      out_on_commit->splice(out_on_commit->end(), i.on_commit);
+      out_on_applied_sync->splice(out_on_applied_sync->end(),
+				  i.on_applied_sync);
+    }
+  }
+
+  Context *get_on_applied() {
+    return C_Contexts::list_to_context(on_applied);
+  }
+  Context *get_on_commit() {
+    return C_Contexts::list_to_context(on_commit);
+  }
+  Context *get_on_applied_sync() {
+    return C_Contexts::list_to_context(on_applied_sync);
+  }
+
+  void set_fadvise_flags(uint32_t flags) {
+    data.fadvise_flags = flags;
+  }
+  void set_fadvise_flag(uint32_t flag) {
+    data.fadvise_flags = data.fadvise_flags | flag;
+  }
+  uint32_t get_fadvise_flags() { return data.fadvise_flags; }
+
+  void swap(Transaction& other) noexcept {
+    std::swap(data, other.data);
+    std::swap(on_applied, other.on_applied);
+    std::swap(on_commit, other.on_commit);
+    std::swap(on_applied_sync, other.on_applied_sync);
+    
+    std::swap(coll_index, other.coll_index);
+    std::swap(object_index, other.object_index);
+    std::swap(coll_id, other.coll_id);
+    std::swap(object_id, other.object_id);
+    op_bl.swap(other.op_bl);
+    data_bl.swap(other.data_bl);
+  }
+
+  void _update_op(Op* op,
+		  vector<__le32> &cm,
+		  vector<__le32> &om) {
+
+    switch (op->op) {
+    case OP_NOP:
+      break;
+
+    case OP_TOUCH:
+    case OP_REMOVE:
+    case OP_SETATTR:
+    case OP_SETATTRS:
+    case OP_RMATTR:
+    case OP_RMATTRS:
+    case OP_COLL_REMOVE:
+    case OP_OMAP_CLEAR:
+    case OP_OMAP_SETKEYS:
+    case OP_OMAP_RMKEYS:
+    case OP_OMAP_RMKEYRANGE:
+    case OP_OMAP_SETHEADER:
+    case OP_WRITE:
+    case OP_ZERO:
+    case OP_TRUNCATE:
+    case OP_SETALLOCHINT:
+      ceph_assert(op->cid < cm.size());
+      ceph_assert(op->oid < om.size());
+      op->cid = cm[op->cid];
+      op->oid = om[op->oid];
+      break;
+
+    case OP_CLONERANGE2:
+    case OP_CLONE:
+      ceph_assert(op->cid < cm.size());
+      ceph_assert(op->oid < om.size());
+      ceph_assert(op->dest_oid < om.size());
+      op->cid = cm[op->cid];
+      op->oid = om[op->oid];
+      op->dest_oid = om[op->dest_oid];
+      break;
+
+    case OP_MKCOLL:
+    case OP_RMCOLL:
+    case OP_COLL_SETATTR:
+    case OP_COLL_RMATTR:
+    case OP_COLL_SETATTRS:
+    case OP_COLL_HINT:
+    case OP_COLL_SET_BITS:
+      ceph_assert(op->cid < cm.size());
+      op->cid = cm[op->cid];
+      break;
+
+    case OP_COLL_ADD:
+      ceph_assert(op->cid < cm.size());
+      ceph_assert(op->oid < om.size());
+      ceph_assert(op->dest_cid < om.size());
+      op->cid = cm[op->cid];
+      op->dest_cid = cm[op->dest_cid];
+      op->oid = om[op->oid];
+      break;
+      
+    case OP_COLL_MOVE_RENAME:
+      ceph_assert(op->cid < cm.size());
+      ceph_assert(op->oid < om.size());
+      ceph_assert(op->dest_cid < cm.size());
+      ceph_assert(op->dest_oid < om.size());
+      op->cid = cm[op->cid];
+      op->oid = om[op->oid];
+      op->dest_cid = cm[op->dest_cid];
+      op->dest_oid = om[op->dest_oid];
+      break;
+      
+    case OP_TRY_RENAME:
+      ceph_assert(op->cid < cm.size());
+      ceph_assert(op->oid < om.size());
+      ceph_assert(op->dest_oid < om.size());
+      op->cid = cm[op->cid];
+      op->oid = om[op->oid];
+      op->dest_oid = om[op->dest_oid];
+      break;
+      
+    case OP_SPLIT_COLLECTION2:
+      ceph_assert(op->cid < cm.size());
+      ceph_assert(op->dest_cid < cm.size());
+      op->cid = cm[op->cid];
+      op->dest_cid = cm[op->dest_cid];
+      break;
+      
+    case OP_MERGE_COLLECTION:
+      ceph_assert(op->cid < cm.size());
+      ceph_assert(op->dest_cid < cm.size());
+      op->cid = cm[op->cid];
+      op->dest_cid = cm[op->dest_cid];
+      break;
+      
+    default:
+      ceph_abort_msg("Unknown OP");
+    }
+  }
+  void _update_op_bl(
+		     bufferlist& bl,
+		     vector<__le32> &cm,
+		     vector<__le32> &om) {
+    for (auto& bp : bl.buffers()) {
+      ceph_assert(bp.length() % sizeof(Op) == 0);
+      
+      char* raw_p = const_cast<char*>(bp.c_str());
+      char* raw_end = raw_p + bp.length();
+      while (raw_p < raw_end) {
+	_update_op(reinterpret_cast<Op*>(raw_p), cm, om);
+	raw_p += sizeof(Op);
+      }
+    }
+  }
+  /// Append the operations of the parameter to this Transaction. Those
+  /// operations are removed from the parameter Transaction
+  void append(Transaction& other) {
+
+    data.ops = data.ops + other.data.ops;
+    if (other.data.largest_data_len > data.largest_data_len) {
+      data.largest_data_len = other.data.largest_data_len;
+      data.largest_data_off = other.data.largest_data_off;
+      data.largest_data_off_in_data_bl = data_bl.length() + other.data.largest_data_off_in_data_bl;
+    }
+    data.fadvise_flags = data.fadvise_flags | other.data.fadvise_flags;
+    on_applied.splice(on_applied.end(), other.on_applied);
+    on_commit.splice(on_commit.end(), other.on_commit);
+    on_applied_sync.splice(on_applied_sync.end(), other.on_applied_sync);
+    
+    //append coll_index & object_index
+    vector<__le32> cm(other.coll_index.size());
+    map<coll_t, __le32>::iterator coll_index_p;
+    for (coll_index_p = other.coll_index.begin();
+	 coll_index_p != other.coll_index.end();
+	 ++coll_index_p) {
+      cm[coll_index_p->second] = _get_coll_id(coll_index_p->first);
+    }
+    
+    vector<__le32> om(other.object_index.size());
+    map<ghobject_t, __le32>::iterator object_index_p;
+    for (object_index_p = other.object_index.begin();
+	 object_index_p != other.object_index.end();
+	 ++object_index_p) {
+      om[object_index_p->second] = _get_object_id(object_index_p->first);
+    }      
+    
+    //the other.op_bl SHOULD NOT be changes during append operation,
+    //we use additional bufferlist to avoid this problem
+    bufferlist other_op_bl;
+    {
+      bufferptr other_op_bl_ptr(other.op_bl.length());
+      other.op_bl.copy(0, other.op_bl.length(), other_op_bl_ptr.c_str());
+      other_op_bl.append(std::move(other_op_bl_ptr));
+    }
+    
+    //update other_op_bl with cm & om
+    //When the other is appended to current transaction, all coll_index and
+    //object_index in other.op_buffer should be updated by new index of the
+    //combined transaction
+    _update_op_bl(other_op_bl, cm, om);
+    
+    //append op_bl
+    op_bl.append(other_op_bl);
+    //append data_bl
+    data_bl.append(other.data_bl);
+  }
+  
+  /** Inquires about the Transaction as a whole. */
+  
+  /// How big is the encoded Transaction buffer?
+  uint64_t get_encoded_bytes() {
+    //layout: data_bl + op_bl + coll_index + object_index + data
+    
+    // coll_index size, object_index size and sizeof(transaction_data)
+    // all here, so they may be computed at compile-time
+    size_t final_size = sizeof(__u32) * 2 + sizeof(data);
+    
+    // coll_index second and object_index second
+    final_size += (coll_index.size() + object_index.size()) * sizeof(__le32);
+    
+    // coll_index first
+    for (auto p = coll_index.begin(); p != coll_index.end(); ++p) {
+      final_size += p->first.encoded_size();
+    }
+    
+    // object_index first
+    for (auto p = object_index.begin(); p != object_index.end(); ++p) {
+      final_size += p->first.encoded_size();
+    }
+    
+    return data_bl.length() +
+      op_bl.length() +
+      final_size;
+  }
+  
+  /// Retain old version for regression testing purposes
+  uint64_t get_encoded_bytes_test() {
+    using ceph::encode;
+    //layout: data_bl + op_bl + coll_index + object_index + data
+    bufferlist bl;
+    encode(coll_index, bl);
+    encode(object_index, bl);
+    
+    return data_bl.length() +
+      op_bl.length() +
+      bl.length() +
+      sizeof(data);
+  }
+  
+  uint64_t get_num_bytes() {
+    return get_encoded_bytes();
+  }
+  /// Size of largest data buffer to the "write" operation encountered so far
+  uint32_t get_data_length() {
+    return data.largest_data_len;
+  }
+  /// offset within the encoded buffer to the start of the largest data buffer
+  /// that's encoded
+  uint32_t get_data_offset() {
+    if (data.largest_data_off_in_data_bl) {
+      return data.largest_data_off_in_data_bl +
+	sizeof(__u8) +      // encode struct_v
+	sizeof(__u8) +      // encode compat_v
+	sizeof(__u32) +     // encode len
+	sizeof(__u32);      // data_bl len
+    }
+    return 0;  // none
+  }
+  /// offset of buffer as aligned to destination within object.
+  int get_data_alignment() {
+    if (!data.largest_data_len)
+      return 0;
+    return (0 - get_data_offset()) & ~CEPH_PAGE_MASK;
+  }
+  /// Is the Transaction empty (no operations)
+  bool empty() {
+    return !data.ops;
+  }
+  /// Number of operations in the transaction
+  int get_num_ops() {
+    return data.ops;
+  }
+  
+  /**
+   * iterator
+   *
+   * Helper object to parse Transactions.
+   *
+   * ObjectStore instances use this object to step down the encoded
+   * buffer decoding operation codes and parameters as we go.
+   *
+   */
+  class iterator {
+    Transaction *t;
+    
+    uint64_t ops;
+    char* op_buffer_p;
+    
+    bufferlist::const_iterator data_bl_p;
+    
+  public:
+    vector<coll_t> colls;
+    vector<ghobject_t> objects;
+    
+  private:
+    explicit iterator(Transaction *t)
+      : t(t),
+	data_bl_p(t->data_bl.cbegin()),
+	colls(t->coll_index.size()),
+	objects(t->object_index.size()) {
+      
+      ops = t->data.ops;
+      op_buffer_p = t->op_bl.c_str();
+      
+      map<coll_t, __le32>::iterator coll_index_p;
+      for (coll_index_p = t->coll_index.begin();
+	   coll_index_p != t->coll_index.end();
+	   ++coll_index_p) {
+	colls[coll_index_p->second] = coll_index_p->first;
+      }
+      
+      map<ghobject_t, __le32>::iterator object_index_p;
+      for (object_index_p = t->object_index.begin();
+	   object_index_p != t->object_index.end();
+	   ++object_index_p) {
+	objects[object_index_p->second] = object_index_p->first;
+      }
+    }
+    
+    friend class Transaction;
+    
+  public:
+    
+    bool have_op() {
+      return ops > 0;
+    }
+    Op* decode_op() {
+      ceph_assert(ops > 0);
+      
+      Op* op = reinterpret_cast<Op*>(op_buffer_p);
+      op_buffer_p += sizeof(Op);
+      ops--;
+      
+      return op;
+    }
+    string decode_string() {
+      using ceph::decode;
+      string s;
+      decode(s, data_bl_p);
+      return s;
+    }
+    void decode_bp(bufferptr& bp) {
+      using ceph::decode;
+      decode(bp, data_bl_p);
+    }
+    void decode_bl(bufferlist& bl) {
+      using ceph::decode;
+      decode(bl, data_bl_p);
+    }
+    void decode_attrset(map<string,bufferptr>& aset) {
+      using ceph::decode;
+      decode(aset, data_bl_p);
+    }
+    void decode_attrset(map<string,bufferlist>& aset) {
+      using ceph::decode;
+      decode(aset, data_bl_p);
+    }
+    void decode_attrset_bl(bufferlist *pbl);
+    void decode_keyset(set<string> &keys){
+      using ceph::decode;
+      decode(keys, data_bl_p);
+    }
+    void decode_keyset_bl(bufferlist *pbl);
+    
+    const ghobject_t &get_oid(__le32 oid_id) {
+      ceph_assert(oid_id < objects.size());
+      return objects[oid_id];
+    }
+    const coll_t &get_cid(__le32 cid_id) {
+      ceph_assert(cid_id < colls.size());
+      return colls[cid_id];
+    }
+    uint32_t get_fadvise_flags() const {
+      return t->get_fadvise_flags();
+    }
+  };
+  
+  iterator begin() {
+    return iterator(this);
+  }
+  
+private:
+  void _build_actions_from_tbl();
+
+  static constexpr size_t OPS_PER_PTR = 32u;
+  /**
+   * Helper functions to encode the various mutation elements of a
+   * transaction.  These are 1:1 with the operation codes (see
+   * enumeration above).  These routines ensure that the
+   * encoder/creator of a transaction gets the right data in the
+   * right place. Sadly, there's no corresponding version nor any
+   * form of seat belts for the decoder.
+   */
+  Op* _get_next_op() {
+    if (op_bl.get_append_buffer_unused_tail_length() < sizeof(Op)) {
+      op_bl.reserve(sizeof(Op) * OPS_PER_PTR);
+    }
+    // append_hole ensures bptr merging. Even huge number of ops
+    // shouldn't result in overpopulating bl::_buffers.
+    char* const p = op_bl.append_hole(sizeof(Op)).c_str();
+    memset(p, 0, sizeof(Op));
+    return reinterpret_cast<Op*>(p);
+  }
+  __le32 _get_coll_id(const coll_t& coll) {
+    map<coll_t, __le32>::iterator c = coll_index.find(coll);
+    if (c != coll_index.end())
+      return c->second;
+    
+    __le32 index_id = coll_id++;
+    coll_index[coll] = index_id;
+    return index_id;
+  }
+  __le32 _get_object_id(const ghobject_t& oid) {
+    map<ghobject_t, __le32>::iterator o = object_index.find(oid);
+    if (o != object_index.end())
+      return o->second;
+    
+    __le32 index_id = object_id++;
+    object_index[oid] = index_id;
+    return index_id;
+  }
+  
+public:
+  /// noop. 'nuf said
+  void nop() {
+    Op* _op = _get_next_op();
+    _op->op = OP_NOP;
+    data.ops = data.ops + 1;
+  }
+  /**
+   * touch
+   *
+   * Ensure the existance of an object in a collection. Create an
+   * empty object if necessary
+   */
+  void touch(const coll_t& cid, const ghobject_t& oid) {
+    Op* _op = _get_next_op();
+    _op->op = OP_TOUCH;
+    _op->cid = _get_coll_id(cid);
+    _op->oid = _get_object_id(oid);
+    data.ops = data.ops + 1;
+  }
+  /**
+   * Write data to an offset within an object. If the object is too
+   * small, it is expanded as needed.  It is possible to specify an
+   * offset beyond the current end of an object and it will be
+   * expanded as needed. Simple implementations of ObjectStore will
+   * just zero the data between the old end of the object and the
+   * newly provided data. More sophisticated implementations of
+   * ObjectStore will omit the untouched data and store it as a
+   * "hole" in the file.
+   *
+   * Note that a 0-length write does not affect the size of the object.
+   */
+  void write(const coll_t& cid, const ghobject_t& oid, uint64_t off, uint64_t len,
+	     const bufferlist& write_data, uint32_t flags = 0) {
+    using ceph::encode;
+    uint32_t orig_len = data_bl.length();
+    Op* _op = _get_next_op();
+    _op->op = OP_WRITE;
+    _op->cid = _get_coll_id(cid);
+    _op->oid = _get_object_id(oid);
+    _op->off = off;
+    _op->len = len;
+    encode(write_data, data_bl);
+    
+    ceph_assert(len == write_data.length());
+    data.fadvise_flags = data.fadvise_flags | flags;
+    if (write_data.length() > data.largest_data_len) {
+      data.largest_data_len = write_data.length();
+      data.largest_data_off = off;
+      // we are about to
+      data.largest_data_off_in_data_bl = orig_len + sizeof(__u32);  
+    }
+    data.ops = data.ops + 1;
+  }
+  /**
+   * zero out the indicated byte range within an object. Some
+   * ObjectStore instances may optimize this to release the
+   * underlying storage space.
+   *
+   * If the zero range extends beyond the end of the object, the object
+   * size is extended, just as if we were writing a buffer full of zeros.
+   * EXCEPT if the length is 0, in which case (just like a 0-length write)
+   * we do not adjust the object size.
+   */
+  void zero(const coll_t& cid, const ghobject_t& oid, uint64_t off, uint64_t len) {
+    Op* _op = _get_next_op();
+    _op->op = OP_ZERO;
+    _op->cid = _get_coll_id(cid);
+    _op->oid = _get_object_id(oid);
+    _op->off = off;
+    _op->len = len;
+    data.ops = data.ops + 1;
+  }
+  /// Discard all data in the object beyond the specified size.
+  void truncate(const coll_t& cid, const ghobject_t& oid, uint64_t off) {
+    Op* _op = _get_next_op();
+    _op->op = OP_TRUNCATE;
+    _op->cid = _get_coll_id(cid);
+    _op->oid = _get_object_id(oid);
+    _op->off = off;
+    data.ops = data.ops + 1;
+  }
+  /// Remove an object. All four parts of the object are removed.
+  void remove(const coll_t& cid, const ghobject_t& oid) {
+    Op* _op = _get_next_op();
+    _op->op = OP_REMOVE;
+    _op->cid = _get_coll_id(cid);
+    _op->oid = _get_object_id(oid);
+    data.ops = data.ops + 1;
+  }
+  /// Set an xattr of an object
+  void setattr(const coll_t& cid, const ghobject_t& oid,
+	       const char* name,
+	       bufferlist& val) {
+    string n(name);
+    setattr(cid, oid, n, val);
+  }
+  /// Set an xattr of an object
+  void setattr(const coll_t& cid, const ghobject_t& oid,
+	       const string& s, bufferlist& val) {
+    using ceph::encode;
+    Op* _op = _get_next_op();
+    _op->op = OP_SETATTR;
+    _op->cid = _get_coll_id(cid);
+    _op->oid = _get_object_id(oid);
+    encode(s, data_bl);
+    encode(val, data_bl);
+    data.ops = data.ops + 1;
+  }
+  /// Set multiple xattrs of an object
+  void setattrs(const coll_t& cid, const ghobject_t& oid,
+		const map<string,bufferptr>& attrset) {
+    using ceph::encode;
+    Op* _op = _get_next_op();
+    _op->op = OP_SETATTRS;
+    _op->cid = _get_coll_id(cid);
+    _op->oid = _get_object_id(oid);
+    encode(attrset, data_bl);
+    data.ops = data.ops + 1;
+  }
+  /// Set multiple xattrs of an object
+  void setattrs(const coll_t& cid, const ghobject_t& oid,
+		const map<string,bufferlist>& attrset) {
+    using ceph::encode;
+    Op* _op = _get_next_op();
+    _op->op = OP_SETATTRS;
+    _op->cid = _get_coll_id(cid);
+    _op->oid = _get_object_id(oid);
+    encode(attrset, data_bl);
+    data.ops = data.ops + 1;
+  }
+  /// remove an xattr from an object
+  void rmattr(const coll_t& cid, const ghobject_t& oid, const char *name) {
+    string n(name);
+    rmattr(cid, oid, n);
+  }
+  /// remove an xattr from an object
+  void rmattr(const coll_t& cid, const ghobject_t& oid, const string& s) {
+    using ceph::encode;
+    Op* _op = _get_next_op();
+    _op->op = OP_RMATTR;
+    _op->cid = _get_coll_id(cid);
+    _op->oid = _get_object_id(oid);
+    encode(s, data_bl);
+    data.ops = data.ops + 1;
+  }
+  /// remove all xattrs from an object
+  void rmattrs(const coll_t& cid, const ghobject_t& oid) {
+    Op* _op = _get_next_op();
+    _op->op = OP_RMATTRS;
+    _op->cid = _get_coll_id(cid);
+    _op->oid = _get_object_id(oid);
+    data.ops = data.ops + 1;
+  }
+  /**
+   * Clone an object into another object.
+   *
+   * Low-cost (e.g., O(1)) cloning (if supported) is best, but
+   * fallback to an O(n) copy is allowed.  All four parts of the
+   * object are cloned (data, xattrs, omap header, omap
+   * entries).
+   *
+   * The destination named object may already exist, in
+   * which case its previous contents are discarded.
+   */
+  void clone(const coll_t& cid, const ghobject_t& oid,
+	     const ghobject_t& noid) {
+    Op* _op = _get_next_op();
+    _op->op = OP_CLONE;
+    _op->cid = _get_coll_id(cid);
+    _op->oid = _get_object_id(oid);
+    _op->dest_oid = _get_object_id(noid);
+    data.ops = data.ops + 1;
+  }
+  /**
+   * Clone a byte range from one object to another.
+   *
+   * The data portion of the destination object receives a copy of a
+   * portion of the data from the source object. None of the other
+   * three parts of an object is copied from the source.
+   *
+   * The destination object size may be extended to the dstoff + len.
+   *
+   * The source range *must* overlap with the source object data. If it does
+   * not the result is undefined.
+   */
+  void clone_range(const coll_t& cid, const ghobject_t& oid,
+		   const ghobject_t& noid,
+		   uint64_t srcoff, uint64_t srclen, uint64_t dstoff) {
+    Op* _op = _get_next_op();
+    _op->op = OP_CLONERANGE2;
+    _op->cid = _get_coll_id(cid);
+    _op->oid = _get_object_id(oid);
+    _op->dest_oid = _get_object_id(noid);
+    _op->off = srcoff;
+    _op->len = srclen;
+    _op->dest_off = dstoff;
+    data.ops = data.ops + 1;
+  }
+  
+  /// Create the collection
+  void create_collection(const coll_t& cid, int bits) {
+    Op* _op = _get_next_op();
+    _op->op = OP_MKCOLL;
+    _op->cid = _get_coll_id(cid);
+    _op->split_bits = bits;
+    data.ops = data.ops + 1;
+  }
+  
+  /**
+   * Give the collection a hint.
+   *
+   * @param cid  - collection id.
+   * @param type - hint type.
+   * @param hint - the hint payload, which contains the customized
+   *               data along with the hint type.
+   */
+  void collection_hint(const coll_t& cid, uint32_t type, const bufferlist& hint) {
+    using ceph::encode;
+    Op* _op = _get_next_op();
+    _op->op = OP_COLL_HINT;
+    _op->cid = _get_coll_id(cid);
+    _op->hint_type = type;
+    encode(hint, data_bl);
+    data.ops = data.ops + 1;
+  }
+  
+  /// remove the collection, the collection must be empty
+  void remove_collection(const coll_t& cid) {
+    Op* _op = _get_next_op();
+    _op->op = OP_RMCOLL;
+    _op->cid = _get_coll_id(cid);
+    data.ops = data.ops + 1;
+  }
+  void collection_move(const coll_t& cid, const coll_t &oldcid,
+		       const ghobject_t& oid)
+    __attribute__ ((deprecated)) {
+    // NOTE: we encode this as a fixed combo of ADD + REMOVE.  they
+    // always appear together, so this is effectively a single MOVE.
+    Op* _op = _get_next_op();
+    _op->op = OP_COLL_ADD;
+    _op->cid = _get_coll_id(oldcid);
+    _op->oid = _get_object_id(oid);
+    _op->dest_cid = _get_coll_id(cid);
+    data.ops = data.ops + 1;
+    
+    _op = _get_next_op();
+    _op->op = OP_COLL_REMOVE;
+    _op->cid = _get_coll_id(oldcid);
+    _op->oid = _get_object_id(oid);
+    data.ops = data.ops + 1;
+  }
+  void collection_move_rename(const coll_t& oldcid, const ghobject_t& oldoid,
+			      const coll_t &cid, const ghobject_t& oid) {
+    Op* _op = _get_next_op();
+    _op->op = OP_COLL_MOVE_RENAME;
+    _op->cid = _get_coll_id(oldcid);
+    _op->oid = _get_object_id(oldoid);
+    _op->dest_cid = _get_coll_id(cid);
+    _op->dest_oid = _get_object_id(oid);
+    data.ops = data.ops + 1;
+  }
+  void try_rename(const coll_t &cid, const ghobject_t& oldoid,
+		  const ghobject_t& oid) {
+    Op* _op = _get_next_op();
+    _op->op = OP_TRY_RENAME;
+    _op->cid = _get_coll_id(cid);
+    _op->oid = _get_object_id(oldoid);
+    _op->dest_oid = _get_object_id(oid);
+    data.ops = data.ops + 1;
+  }
+  
+  /// Remove omap from oid
+  void omap_clear(
+    const coll_t &cid,           ///< [in] Collection containing oid
+    const ghobject_t &oid  ///< [in] Object from which to remove omap
+    ) {
+    Op* _op = _get_next_op();
+    _op->op = OP_OMAP_CLEAR;
+    _op->cid = _get_coll_id(cid);
+    _op->oid = _get_object_id(oid);
+    data.ops = data.ops + 1;
+  }
+  /// Set keys on oid omap.  Replaces duplicate keys.
+  void omap_setkeys(
+    const coll_t& cid,                           ///< [in] Collection containing oid
+    const ghobject_t &oid,                ///< [in] Object to update
+    const map<string, bufferlist> &attrset ///< [in] Replacement keys and values
+    ) {
+    using ceph::encode;
+    Op* _op = _get_next_op();
+    _op->op = OP_OMAP_SETKEYS;
+    _op->cid = _get_coll_id(cid);
+    _op->oid = _get_object_id(oid);
+    encode(attrset, data_bl);
+    data.ops = data.ops + 1;
+  }
+
+    /// Set keys on an oid omap (bufferlist variant).
+  void omap_setkeys(
+    const coll_t &cid,                           ///< [in] Collection containing oid
+    const ghobject_t &oid,                ///< [in] Object to update
+    const bufferlist &attrset_bl          ///< [in] Replacement keys and values
+  ) {
+    Op* _op = _get_next_op();
+    _op->op = OP_OMAP_SETKEYS;
+    _op->cid = _get_coll_id(cid);
+    _op->oid = _get_object_id(oid);
+    data_bl.append(attrset_bl);
+    data.ops = data.ops + 1;
+  }
+
+  /// Remove keys from oid omap
+  void omap_rmkeys(
+    const coll_t &cid,             ///< [in] Collection containing oid
+    const ghobject_t &oid,  ///< [in] Object from which to remove the omap
+    const set<string> &keys ///< [in] Keys to clear
+    ) {
+    using ceph::encode;
+    Op* _op = _get_next_op();
+    _op->op = OP_OMAP_RMKEYS;
+    _op->cid = _get_coll_id(cid);
+    _op->oid = _get_object_id(oid);
+    encode(keys, data_bl);
+    data.ops = data.ops + 1;
+  }
+
+  /// Remove keys from oid omap
+  void omap_rmkeys(
+    const coll_t &cid,             ///< [in] Collection containing oid
+    const ghobject_t &oid,  ///< [in] Object from which to remove the omap
+    const bufferlist &keys_bl ///< [in] Keys to clear
+    ) {
+    Op* _op = _get_next_op();
+    _op->op = OP_OMAP_RMKEYS;
+    _op->cid = _get_coll_id(cid);
+    _op->oid = _get_object_id(oid);
+    data_bl.append(keys_bl);
+    data.ops = data.ops + 1;
+  }
+  
+  /// Remove key range from oid omap
+  void omap_rmkeyrange(
+    const coll_t &cid,             ///< [in] Collection containing oid
+    const ghobject_t &oid,  ///< [in] Object from which to remove the omap keys
+    const string& first,    ///< [in] first key in range
+    const string& last      ///< [in] first key past range, range is [first,last)
+    ) {
+    using ceph::encode;
+    Op* _op = _get_next_op();
+    _op->op = OP_OMAP_RMKEYRANGE;
+    _op->cid = _get_coll_id(cid);
+    _op->oid = _get_object_id(oid);
+    encode(first, data_bl);
+    encode(last, data_bl);
+    data.ops = data.ops + 1;
+  }
+
+  /// Set omap header
+  void omap_setheader(
+    const coll_t &cid,             ///< [in] Collection containing oid
+    const ghobject_t &oid,  ///< [in] Object
+    const bufferlist &bl    ///< [in] Header value
+    ) {
+    using ceph::encode;
+    Op* _op = _get_next_op();
+    _op->op = OP_OMAP_SETHEADER;
+    _op->cid = _get_coll_id(cid);
+    _op->oid = _get_object_id(oid);
+    encode(bl, data_bl);
+    data.ops = data.ops + 1;
+  }
+
+  /// Split collection based on given prefixes, objects matching the specified
+  /// bits/rem are moved to the new collection
+  void split_collection(
+    const coll_t &cid,
+    uint32_t bits,
+    uint32_t rem,
+    const coll_t &destination) {
+    Op* _op = _get_next_op();
+    _op->op = OP_SPLIT_COLLECTION2;
+    _op->cid = _get_coll_id(cid);
+    _op->dest_cid = _get_coll_id(destination);
+    _op->split_bits = bits;
+    _op->split_rem = rem;
+    data.ops = data.ops + 1;
+  }
+
+  /// Merge collection into another.
+  void merge_collection(
+    coll_t cid,
+    coll_t destination,
+    uint32_t bits) {
+    Op* _op = _get_next_op();
+    _op->op = OP_MERGE_COLLECTION;
+    _op->cid = _get_coll_id(cid);
+    _op->dest_cid = _get_coll_id(destination);
+    _op->split_bits = bits;
+    data.ops = data.ops + 1;
+  }
+
+  void collection_set_bits(
+    const coll_t &cid,
+    int bits) {
+    Op* _op = _get_next_op();
+    _op->op = OP_COLL_SET_BITS;
+    _op->cid = _get_coll_id(cid);
+    _op->split_bits = bits;
+    data.ops = data.ops + 1;
+  }
+
+  /// Set allocation hint for an object
+  /// make 0 values(expected_object_size, expected_write_size) noops for all implementations
+  void set_alloc_hint(
+    const coll_t &cid,
+    const ghobject_t &oid,
+    uint64_t expected_object_size,
+    uint64_t expected_write_size,
+    uint32_t flags
+  ) {
+    Op* _op = _get_next_op();
+    _op->op = OP_SETALLOCHINT;
+    _op->cid = _get_coll_id(cid);
+    _op->oid = _get_object_id(oid);
+    _op->expected_object_size = expected_object_size;
+    _op->expected_write_size = expected_write_size;
+    _op->alloc_hint_flags = flags;
+    data.ops = data.ops + 1;
+  }
+
+  void encode(bufferlist& bl) const {
+    //layout: data_bl + op_bl + coll_index + object_index + data
+    ENCODE_START(9, 9, bl);
+    encode(data_bl, bl);
+    encode(op_bl, bl);
+    encode(coll_index, bl);
+    encode(object_index, bl);
+    data.encode(bl);
+    ENCODE_FINISH(bl);
+  }
+
+  void decode(bufferlist::const_iterator &bl) {
+    DECODE_START(9, bl);
+    DECODE_OLDEST(9);
+
+    decode(data_bl, bl);
+    decode(op_bl, bl);
+    decode(coll_index, bl);
+    decode(object_index, bl);
+    data.decode(bl);
+    coll_id = coll_index.size();
+    object_id = object_index.size();
+
+    DECODE_FINISH(bl);
+  }
+
+  void dump(ceph::Formatter *f);
+};
+}
diff --git a/src/crimson/os/cyan_collection.cc b/src/crimson/os/cyan_collection.cc
new file mode 100644
index 00000000..82403dbc
--- /dev/null
+++ b/src/crimson/os/cyan_collection.cc
@@ -0,0 +1,76 @@
+#include "cyan_collection.h"
+
+#include "cyan_object.h"
+
+namespace ceph::os
+{
+
+Collection::Collection(const coll_t& c)
+  : cid{c}
+{}
+
+Collection::~Collection() = default;
+
+Collection::ObjectRef Collection::create_object() const
+{
+  return new ceph::os::Object{};
+}
+
+Collection::ObjectRef Collection::get_object(ghobject_t oid)
+{
+  auto o = object_hash.find(oid);
+  if (o == object_hash.end())
+    return ObjectRef();
+  return o->second;
+}
+
+Collection::ObjectRef Collection::get_or_create_object(ghobject_t oid)
+{
+  auto result = object_hash.emplace(oid, ObjectRef{});
+  if (result.second)
+    object_map[oid] = result.first->second = create_object();
+  return result.first->second;
+}
+
+uint64_t Collection::used_bytes() const
+{
+  uint64_t result = 0;
+  for (auto& obj : object_map) {
+    result += obj.second->get_size();
+  }
+  return result;
+}
+
+void Collection::encode(bufferlist& bl) const
+{
+  ENCODE_START(1, 1, bl);
+  encode(xattr, bl);
+  encode(use_page_set, bl);
+  uint32_t s = object_map.size();
+  encode(s, bl);
+  for (auto& [oid, obj] : object_map) {
+    encode(oid, bl);
+    obj->encode(bl);
+  }
+  ENCODE_FINISH(bl);
+}
+
+void Collection::decode(bufferlist::const_iterator& p)
+{
+  DECODE_START(1, p);
+  decode(xattr, p);
+  decode(use_page_set, p);
+  uint32_t s;
+  decode(s, p);
+  while (s--) {
+    ghobject_t k;
+    decode(k, p);
+    auto o = create_object();
+    o->decode(p);
+    object_map.insert(make_pair(k, o));
+    object_hash.insert(make_pair(k, o));
+  }
+  DECODE_FINISH(p);
+}
+
+}
diff --git a/src/crimson/os/cyan_collection.h b/src/crimson/os/cyan_collection.h
new file mode 100644
index 00000000..78f1aa0a
--- /dev/null
+++ b/src/crimson/os/cyan_collection.h
@@ -0,0 +1,55 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+
+#include <string>
+#include <unordered_map>
+#include <boost/intrusive_ptr.hpp>
+#include <boost/smart_ptr/intrusive_ref_counter.hpp>
+
+#include "include/buffer.h"
+#include "osd/osd_types.h"
+
+namespace ceph::os {
+
+class Object;
+/**
+ * a collection also orders transactions
+ *
+ * Any transactions queued under a given collection will be applied in
+ * sequence.  Transactions queued under different collections may run
+ * in parallel.
+ *
+ * ObjectStore users my get collection handles with open_collection() (or,
+ * for bootstrapping a new collection, create_new_collection()).
+ */
+struct Collection : public boost::intrusive_ref_counter<
+  Collection,
+  boost::thread_unsafe_counter>
+{
+  using ObjectRef = boost::intrusive_ptr<Object>;
+  const coll_t cid;
+  int bits = 0;
+  // always use bufferlist object for testing
+  bool use_page_set = false;
+  std::unordered_map<ghobject_t, ObjectRef> object_hash;  ///< for lookup
+  std::map<ghobject_t, ObjectRef> object_map;        ///< for iteration
+  std::map<std::string,bufferptr> xattr;
+  bool exists = true;
+
+  Collection(const coll_t& c);
+  ~Collection();
+
+  ObjectRef create_object() const;
+  ObjectRef get_object(ghobject_t oid);
+  ObjectRef get_or_create_object(ghobject_t oid);
+  uint64_t used_bytes() const;
+
+  const coll_t &get_cid() const {
+    return cid;
+  }
+
+  void encode(bufferlist& bl) const;
+  void decode(bufferlist::const_iterator& p);
+};
+
+}
diff --git a/src/crimson/os/cyan_object.cc b/src/crimson/os/cyan_object.cc
new file mode 100644
index 00000000..1612cebe
--- /dev/null
+++ b/src/crimson/os/cyan_object.cc
@@ -0,0 +1,88 @@
+#include "cyan_object.h"
+#include "include/encoding.h"
+
+namespace ceph::os {
+
+size_t Object::get_size() const {
+  return data.length();
+}
+
+int Object::read(uint64_t offset, uint64_t len, bufferlist &bl)
+{
+  bl.substr_of(data, offset, len);
+  return bl.length();
+}
+
+int Object::write(uint64_t offset, const bufferlist &src)
+{
+  unsigned len = src.length();
+  // before
+  bufferlist newdata;
+  if (get_size() >= offset) {
+    newdata.substr_of(data, 0, offset);
+  } else {
+    if (get_size()) {
+      newdata.substr_of(data, 0, get_size());
+    }
+    newdata.append_zero(offset - get_size());
+  }
+
+  newdata.append(src);
+
+  // after
+  if (get_size() > offset + len) {
+    bufferlist tail;
+    tail.substr_of(data, offset + len, get_size() - (offset + len));
+    newdata.append(tail);
+  }
+
+  data.claim(newdata);
+  return 0;
+}
+
+int Object::clone(Object *src, uint64_t srcoff, uint64_t len,
+                  uint64_t dstoff)
+{
+  bufferlist bl;
+  if (srcoff == dstoff && len == src->get_size()) {
+    data = src->data;
+    return 0;
+  }
+  bl.substr_of(src->data, srcoff, len);
+  return write(dstoff, bl);
+
+}
+
+int Object::truncate(uint64_t size)
+{
+  if (get_size() > size) {
+    bufferlist bl;
+    bl.substr_of(data, 0, size);
+    data.claim(bl);
+  } else if (get_size() == size) {
+    // do nothing
+  } else {
+    data.append_zero(size - get_size());
+  }
+  return 0;
+}
+
+void Object::encode(bufferlist& bl) const {
+  ENCODE_START(1, 1, bl);
+  encode(data, bl);
+  encode(xattr, bl);
+  encode(omap_header, bl);
+  encode(omap, bl);
+  ENCODE_FINISH(bl);
+}
+
+void Object::decode(bufferlist::const_iterator& p) {
+  DECODE_START(1, p);
+  decode(data, p);
+  decode(xattr, p);
+  decode(omap_header, p);
+  decode(omap, p);
+  DECODE_FINISH(p);
+}
+
+}
diff --git a/src/crimson/os/cyan_object.h b/src/crimson/os/cyan_object.h
new file mode 100644
index 00000000..6846b1a4
--- /dev/null
+++ b/src/crimson/os/cyan_object.h
@@ -0,0 +1,38 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+#include <cstddef>
+#include <map>
+#include <string>
+#include <boost/intrusive_ptr.hpp>
+#include <boost/smart_ptr/intrusive_ref_counter.hpp>
+#include "include/buffer.h"
+
+namespace ceph::os {
+
+struct Object : public boost::intrusive_ref_counter<
+  Object,
+  boost::thread_unsafe_counter>
+{
+  using bufferlist = ceph::bufferlist;
+
+  bufferlist data;
+  std::map<std::string,bufferptr> xattr;
+  bufferlist omap_header;
+  std::map<std::string,bufferlist> omap;
+
+  typedef boost::intrusive_ptr<Object> Ref;
+
+  Object() = default;
+
+  // interface for object data
+  size_t get_size() const;
+  int read(uint64_t offset, uint64_t len, bufferlist &bl);
+  int write(uint64_t offset, const bufferlist &bl);
+  int clone(Object *src, uint64_t srcoff, uint64_t len,
+	     uint64_t dstoff);
+  int truncate(uint64_t offset);
+
+  void encode(bufferlist& bl) const;
+  void decode(bufferlist::const_iterator& p);
+};
+}
diff --git a/src/crimson/os/cyan_store.cc b/src/crimson/os/cyan_store.cc
new file mode 100644
index 00000000..68ccae88
--- /dev/null
+++ b/src/crimson/os/cyan_store.cc
@@ -0,0 +1,277 @@
+#include "cyan_store.h"
+
+#include <fmt/format.h>
+
+#include "common/safe_io.h"
+
+#include "crimson/os/cyan_collection.h"
+#include "crimson/os/cyan_object.h"
+#include "crimson/os/Transaction.h"
+
+namespace {
+  seastar::logger& logger() {
+    return ceph::get_logger(ceph_subsys_filestore);
+  }
+}
+
+namespace ceph::os {
+
+using ObjectRef = boost::intrusive_ptr<Object>;
+
+CyanStore::CyanStore(const std::string& path)
+  : path{path}
+{}
+
+CyanStore::~CyanStore() = default;
+
+seastar::future<> CyanStore::mount()
+{
+  bufferlist bl;
+  string fn = path + "/collections";
+  string err;
+  if (int r = bl.read_file(fn.c_str(), &err); r < 0) {
+    throw std::runtime_error("read_file");
+  }
+
+  set<coll_t> collections;
+  auto p = bl.cbegin();
+  decode(collections, p);
+
+  for (auto& coll : collections) {
+    string fn = fmt::format("{}/{}", path, coll);
+    bufferlist cbl;
+    if (int r = cbl.read_file(fn.c_str(), &err); r < 0) {
+      throw std::runtime_error("read_file");
+    }
+    CollectionRef c{new Collection{coll}};
+    auto p = cbl.cbegin();
+    c->decode(p);
+    coll_map[coll] = c;
+    used_bytes += c->used_bytes();
+  }
+  return seastar::now();
+}
+
+seastar::future<> CyanStore::umount()
+{
+  set<coll_t> collections;
+  for (auto& [col, ch] : coll_map) {
+    collections.insert(col);
+    bufferlist bl;
+    ceph_assert(ch);
+    ch->encode(bl);
+    string fn = fmt::format("{}/{}", path, col);
+    if (int r = bl.write_file(fn.c_str()); r < 0) {
+      throw std::runtime_error("write_file");
+    }
+  }
+
+  string fn = path + "/collections";
+  bufferlist bl;
+  encode(collections, bl);
+  if (int r = bl.write_file(fn.c_str()); r < 0) {
+    throw std::runtime_error("write_file");
+  }
+  return seastar::now();
+}
+
+seastar::future<> CyanStore::mkfs(uuid_d osd_fsid)
+{
+  string fsid_str;
+  int r = read_meta("fsid", &fsid_str);
+  if (r == -ENOENT) {
+    write_meta("fsid", fmt::format("{}", osd_fsid));
+  } else if (r < 0) {
+    throw std::runtime_error("read_meta");
+  } else {
+    logger().error("{} already has fsid {}", __func__, fsid_str);
+    throw std::runtime_error("mkfs");
+  }
+
+  string fn = path + "/collections";
+  bufferlist bl;
+  set<coll_t> collections;
+  encode(collections, bl);
+  r = bl.write_file(fn.c_str());
+  if (r < 0)
+    throw std::runtime_error("write_file");
+
+  write_meta("type", "memstore");
+  return seastar::now();
+}
+
+CyanStore::CollectionRef CyanStore::create_new_collection(const coll_t& cid)
+{
+  auto c = new Collection{cid};
+  return new_coll_map[cid] = c;
+}
+
+CyanStore::CollectionRef CyanStore::open_collection(const coll_t& cid)
+{
+  auto cp = coll_map.find(cid);
+  if (cp == coll_map.end())
+    return {};
+  return cp->second;
+}
+
+std::vector<coll_t> CyanStore::list_collections()
+{
+  std::vector<coll_t> collections;
+  for (auto& coll : coll_map) {
+    collections.push_back(coll.first);
+  }
+  return collections;
+}
+
+seastar::future<bufferlist> CyanStore::read(CollectionRef c,
+                                            const ghobject_t& oid,
+                                            uint64_t offset,
+                                            size_t len,
+                                            uint32_t op_flags)
+{
+  logger().info("{} {} {} {}~{}",
+                __func__, c->cid, oid, offset, len);
+  if (!c->exists) {
+    throw std::runtime_error(fmt::format("collection does not exist: {}", c->cid));
+  }
+  ObjectRef o = c->get_object(oid);
+  if (!o) {
+    throw std::runtime_error(fmt::format("object does not exist: {}", oid));
+  }
+  if (offset >= o->get_size())
+    return seastar::make_ready_future<bufferlist>();
+  size_t l = len;
+  if (l == 0 && offset == 0)  // note: len == 0 means read the entire object
+    l = o->get_size();
+  else if (offset + l > o->get_size())
+    l = o->get_size() - offset;
+  bufferlist bl;
+  if (int r = o->read(offset, l, bl); r < 0) {
+    throw std::runtime_error("read");
+  }
+  return seastar::make_ready_future<bufferlist>(std::move(bl));
+}
+
+seastar::future<CyanStore::omap_values_t>
+CyanStore::omap_get_values(CollectionRef c,
+                           const ghobject_t& oid,
+                           std::vector<std::string>&& keys)
+{
+  logger().info("{} {} {}",
+                __func__, c->cid, oid);
+  auto o = c->get_object(oid);
+  if (!o) {
+    throw std::runtime_error(fmt::format("object does not exist: {}", oid));
+  }
+  omap_values_t values;
+  for (auto& key : keys) {
+    if (auto found = o->omap.find(key); found != o->omap.end()) {
+      values.insert(*found);
+    }
+  }
+  return seastar::make_ready_future<omap_values_t>(std::move(values));
+}
+
+seastar::future<> CyanStore::do_transaction(CollectionRef ch,
+                                            Transaction&& t)
+{
+  auto i = t.begin();
+  while (i.have_op()) {
+    Transaction::Op* op = i.decode_op();
+    int r = 0;
+    switch (op->op) {
+    case Transaction::OP_NOP:
+      break;
+    case Transaction::OP_WRITE:
+      {
+        coll_t cid = i.get_cid(op->cid);
+        ghobject_t oid = i.get_oid(op->oid);
+        uint64_t off = op->off;
+        uint64_t len = op->len;
+        uint32_t fadvise_flags = i.get_fadvise_flags();
+        bufferlist bl;
+        i.decode_bl(bl);
+        r = _write(cid, oid, off, len, bl, fadvise_flags);
+      }
+      break;
+    case Transaction::OP_MKCOLL:
+      {
+        coll_t cid = i.get_cid(op->cid);
+        r = _create_collection(cid, op->split_bits);
+      }
+      break;
+    default:
+      logger().error("bad op {}", static_cast<unsigned>(op->op));
+      abort();
+    }
+    if (r < 0) {
+      abort();
+    }
+  }
+  return seastar::now();
+}
+
+int CyanStore::_write(const coll_t& cid, const ghobject_t& oid,
+                       uint64_t offset, size_t len, const bufferlist& bl,
+                       uint32_t fadvise_flags)
+{
+  logger().info("{} {} {} {} ~ {}",
+                __func__, cid, oid, offset, len);
+  assert(len == bl.length());
+
+  auto c = open_collection(cid);
+  if (!c)
+    return -ENOENT;
+
+  ObjectRef o = c->get_or_create_object(oid);
+  if (len > 0) {
+    const ssize_t old_size = o->get_size();
+    o->write(offset, bl);
+    used_bytes += (o->get_size() - old_size);
+  }
+
+  return 0;
+}
+
+int CyanStore::_create_collection(const coll_t& cid, int bits)
+{
+  auto result = coll_map.insert(std::make_pair(cid, CollectionRef()));
+  if (!result.second)
+    return -EEXIST;
+  auto p = new_coll_map.find(cid);
+  assert(p != new_coll_map.end());
+  result.first->second = p->second;
+  result.first->second->bits = bits;
+  new_coll_map.erase(p);
+  return 0;
+}
+
+void CyanStore::write_meta(const std::string& key,
+                           const std::string& value)
+{
+  std::string v = value;
+  v += "\n";
+  if (int r = safe_write_file(path.c_str(), key.c_str(),
+                              v.c_str(), v.length(), 0600);
+      r < 0) {
+    throw std::runtime_error{fmt::format("unable to write_meta({})", key)};
+  }
+}
+
+int CyanStore::read_meta(const std::string& key,
+                          std::string* value)
+{
+  char buf[4096];
+  int r = safe_read_file(path.c_str(), key.c_str(),
+                         buf, sizeof(buf));
+  if (r <= 0) {
+    return r;
+  }
+  // drop trailing newlines
+  while (r && isspace(buf[r-1])) {
+    --r;
+  }
+  *value = string{buf, static_cast<size_t>(r)};
+  return 0;
+}
+}
diff --git a/src/crimson/os/cyan_store.h b/src/crimson/os/cyan_store.h
new file mode 100644
index 00000000..0b7f3d87
--- /dev/null
+++ b/src/crimson/os/cyan_store.h
@@ -0,0 +1,63 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+
+#pragma once
+
+#include <string>
+#include <unordered_map>
+#include <map>
+#include <vector>
+#include <seastar/core/future.hh>
+#include "osd/osd_types.h"
+#include "include/uuid.h"
+
+namespace ceph::os {
+
+class Collection;
+class Transaction;
+
+// a just-enough store for reading/writing the superblock
+class CyanStore {
+  using CollectionRef = boost::intrusive_ptr<Collection>;
+  const std::string path;
+  std::unordered_map<coll_t, CollectionRef> coll_map;
+  std::map<coll_t,CollectionRef> new_coll_map;
+  uint64_t used_bytes = 0;
+
+public:
+  CyanStore(const std::string& path);
+  ~CyanStore();
+
+  seastar::future<> mount();
+  seastar::future<> umount();
+
+  seastar::future<> mkfs(uuid_d osd_fsid);
+  seastar::future<bufferlist> read(CollectionRef c,
+				   const ghobject_t& oid,
+				   uint64_t offset,
+				   size_t len,
+				   uint32_t op_flags = 0);
+  using omap_values_t = std::map<std::string,bufferlist, std::less<>>;
+  seastar::future<omap_values_t> omap_get_values(
+    CollectionRef c,
+    const ghobject_t& oid,
+    std::vector<std::string>&& keys);
+  CollectionRef create_new_collection(const coll_t& cid);
+  CollectionRef open_collection(const coll_t& cid);
+  std::vector<coll_t> list_collections();
+
+  seastar::future<> do_transaction(CollectionRef ch,
+				   Transaction&& txn);
+
+  void write_meta(const std::string& key,
+		  const std::string& value);
+  int read_meta(const std::string& key, std::string* value);
+
+private:
+  int _write(const coll_t& cid, const ghobject_t& oid,
+	     uint64_t offset, size_t len, const bufferlist& bl,
+	     uint32_t fadvise_flags);
+  int _create_collection(const coll_t& cid, int bits);
+};
+
+}
diff --git a/src/crimson/osd/CMakeLists.txt b/src/crimson/osd/CMakeLists.txt
new file mode 100644
index 00000000..e86a11b5
--- /dev/null
+++ b/src/crimson/osd/CMakeLists.txt
@@ -0,0 +1,10 @@
+add_executable(crimson-osd
+  chained_dispatchers.cc
+  heartbeat.cc
+  main.cc
+  osd.cc
+  osd_meta.cc
+  pg.cc
+  pg_meta.cc)
+target_link_libraries(crimson-osd
+  crimson-common crimson-os crimson)
diff --git a/src/crimson/osd/chained_dispatchers.cc b/src/crimson/osd/chained_dispatchers.cc
new file mode 100644
index 00000000..da4aa269
--- /dev/null
+++ b/src/crimson/osd/chained_dispatchers.cc
@@ -0,0 +1,72 @@
+#include "chained_dispatchers.h"
+#include "crimson/net/Connection.h"
+
+
+seastar::future<>
+ChainedDispatchers::ms_dispatch(ceph::net::ConnectionRef conn,
+                                MessageRef m) {
+  return seastar::do_for_each(dispatchers, [conn, m](Dispatcher* dispatcher) {
+    return dispatcher->ms_dispatch(conn, m);
+  });
+}
+
+seastar::future<>
+ChainedDispatchers::ms_handle_accept(ceph::net::ConnectionRef conn) {
+  return seastar::do_for_each(dispatchers, [conn](Dispatcher* dispatcher) {
+    return dispatcher->ms_handle_accept(conn);
+  });
+}
+
+seastar::future<>
+ChainedDispatchers::ms_handle_connect(ceph::net::ConnectionRef conn) {
+  return seastar::do_for_each(dispatchers, [conn](Dispatcher* dispatcher) {
+    return dispatcher->ms_handle_connect(conn);
+  });
+}
+
+seastar::future<>
+ChainedDispatchers::ms_handle_reset(ceph::net::ConnectionRef conn) {
+  return seastar::do_for_each(dispatchers, [conn](Dispatcher* dispatcher) {
+    return dispatcher->ms_handle_reset(conn);
+  });
+}
+
+seastar::future<>
+ChainedDispatchers::ms_handle_remote_reset(ceph::net::ConnectionRef conn) {
+  return seastar::do_for_each(dispatchers, [conn](Dispatcher* dispatcher) {
+    return dispatcher->ms_handle_remote_reset(conn);
+  });
+}
+
+seastar::future<std::unique_ptr<AuthAuthorizer>>
+ChainedDispatchers::ms_get_authorizer(peer_type_t peer_type)
+{
+  // since dispatcher returns a nullptr if it does not have the authorizer,
+  // let's use the chain-of-responsibility pattern here.
+  struct Params {
+    peer_type_t peer_type;
+    std::deque<Dispatcher*>::iterator first, last;
+  } params = {peer_type, dispatchers.begin(), dispatchers.end()};
+  return seastar::do_with(Params{params}, [this] (Params& params) {
+    using result_t = std::unique_ptr<AuthAuthorizer>;
+    return seastar::repeat_until_value([&] () {
+      auto& first = params.first;
+      if (first == params.last) {
+        // just give up
+        return seastar::make_ready_future<std::optional<result_t>>(result_t{});
+      } else {
+        return (*first)->ms_get_authorizer(params.peer_type)
+          .then([&] (auto&& auth)-> std::optional<result_t> {
+          if (auth) {
+            // hooray!
+            return std::move(auth);
+          } else {
+            // try next one
+            ++first;
+            return {};
+          }
+        });
+      }
+    });
+  });
+}	 
diff --git a/src/crimson/osd/chained_dispatchers.h b/src/crimson/osd/chained_dispatchers.h
new file mode 100644
index 00000000..c3040836
--- /dev/null
+++ b/src/crimson/osd/chained_dispatchers.h
@@ -0,0 +1,32 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:nil -*- 
+// vim: ts=8 sw=2 smarttab
+
+#pragma once
+
+#include <deque>
+#include "crimson/net/Dispatcher.h"
+
+// in existing Messenger, dispatchers are put into a chain as described by
+// chain-of-responsibility pattern. we could do the same to stop processing
+// the message once any of the dispatchers claims this message, and prevent
+// other dispatchers from reading it. but this change is more involved as
+// it requires changing the ms_ methods to return a bool. so as an intermediate 
+// solution, we are using an observer dispatcher to notify all the interested
+// or unintersted parties.
+class ChainedDispatchers : public ceph::net::Dispatcher {
+  std::deque<Dispatcher*> dispatchers;
+public:
+  void push_front(Dispatcher* dispatcher) {
+    dispatchers.push_front(dispatcher);
+  }
+  void push_back(Dispatcher* dispatcher) {
+    dispatchers.push_back(dispatcher);
+  }
+  seastar::future<> ms_dispatch(ceph::net::ConnectionRef conn, MessageRef m) override;
+  seastar::future<> ms_handle_accept(ceph::net::ConnectionRef conn) override;
+  seastar::future<> ms_handle_connect(ceph::net::ConnectionRef conn) override;
+  seastar::future<> ms_handle_reset(ceph::net::ConnectionRef conn) override;
+  seastar::future<> ms_handle_remote_reset(ceph::net::ConnectionRef conn) override;
+  seastar::future<std::unique_ptr<AuthAuthorizer>>
+  ms_get_authorizer(peer_type_t peer_type) override;
+};
diff --git a/src/crimson/osd/heartbeat.cc b/src/crimson/osd/heartbeat.cc
new file mode 100644
index 00000000..6dfefb3b
--- /dev/null
+++ b/src/crimson/osd/heartbeat.cc
@@ -0,0 +1,415 @@
+#include "heartbeat.h"
+
+#include <boost/range/join.hpp>
+
+#include "messages/MOSDPing.h"
+#include "messages/MOSDFailure.h"
+
+#include "crimson/common/config_proxy.h"
+#include "crimson/net/Connection.h"
+#include "crimson/net/Messenger.h"
+#include "crimson/osd/osdmap_service.h"
+#include "crimson/mon/MonClient.h"
+
+#include "osd/OSDMap.h"
+
+using ceph::common::local_conf;
+
+namespace {
+  seastar::logger& logger() {
+    return ceph::get_logger(ceph_subsys_osd);
+  }
+
+  template<typename Message, typename... Args>
+  Ref<Message> make_message(Args&&... args)
+  {
+    return {new Message{std::forward<Args>(args)...}, false};
+  }
+}
+
+Heartbeat::Heartbeat(int whoami,
+                     uint32_t nonce,
+                     const OSDMapService& service,
+                     ceph::mon::Client& monc)
+  : whoami{whoami},
+    nonce{nonce},
+    service{service},
+    monc{monc},
+    timer{[this] {send_heartbeats();}}
+{}
+
+seastar::future<> Heartbeat::start(entity_addrvec_t front_addrs,
+                                   entity_addrvec_t back_addrs)
+{
+  logger().info("heartbeat: start");
+  // i only care about the address, so any unused port would work
+  for (auto& addr : boost::join(front_addrs.v, back_addrs.v)) {
+    addr.set_port(0);
+  }
+  return seastar::when_all_succeed(
+      ceph::net::Messenger::create(entity_name_t::OSD(whoami),
+                                   "hb_front",
+                                   nonce,
+                                   seastar::engine().cpu_id())
+        .then([this, front_addrs] (auto msgr) {
+          front_msgr = msgr;
+          return start_messenger(front_msgr, front_addrs);
+        }),
+      ceph::net::Messenger::create(entity_name_t::OSD(whoami),
+                                   "hb_back",
+                                   nonce,
+                                   seastar::engine().cpu_id())
+        .then([this, back_addrs] (auto msgr) {
+          back_msgr = msgr;
+          return start_messenger(back_msgr, back_addrs);
+        }))
+    .then([this] {
+      timer.arm_periodic(
+        std::chrono::seconds(local_conf()->osd_heartbeat_interval));
+    });
+}
+
+seastar::future<>
+Heartbeat::start_messenger(ceph::net::Messenger* msgr,
+                           const entity_addrvec_t& addrs)
+{
+  if (local_conf()->ms_crc_data) {
+    msgr->set_crc_data();
+  }
+  if (local_conf()->ms_crc_header) {
+    msgr->set_crc_header();
+  }
+  return msgr->try_bind(addrs,
+                        local_conf()->ms_bind_port_min,
+                        local_conf()->ms_bind_port_max).then([msgr, this] {
+    return msgr->start(this);
+  });
+}
+
+seastar::future<> Heartbeat::stop()
+{
+  return seastar::when_all_succeed(front_msgr->shutdown(),
+                                   back_msgr->shutdown());
+}
+
+const entity_addrvec_t& Heartbeat::get_front_addrs() const
+{
+  return front_msgr->get_myaddrs();
+}
+
+const entity_addrvec_t& Heartbeat::get_back_addrs() const
+{
+  return back_msgr->get_myaddrs();
+}
+
+seastar::future<> Heartbeat::add_peer(osd_id_t peer, epoch_t epoch)
+{
+  auto found = peers.find(peer);
+  if (found == peers.end()) {
+    logger().info("add_peer({})", peer);
+    auto osdmap = service.get_map();
+    // TODO: msgr v2
+    return seastar::when_all_succeed(
+        front_msgr->connect(osdmap->get_hb_front_addrs(peer).legacy_addr(),
+                            CEPH_ENTITY_TYPE_OSD),
+        back_msgr->connect(osdmap->get_hb_back_addrs(peer).legacy_addr(),
+                           CEPH_ENTITY_TYPE_OSD))
+      .then([this, peer, epoch] (auto xcon_front, auto xcon_back) {
+        PeerInfo info;
+        // sharded-messenger compatible mode
+        info.con_front = xcon_front->release();
+        info.con_back = xcon_back->release();
+        info.epoch = epoch;
+        peers.emplace(peer, std::move(info));
+      });
+  } else {
+    found->second.epoch = epoch;
+    return seastar::now();
+  }
+}
+
+seastar::future<Heartbeat::osds_t> Heartbeat::remove_down_peers()
+{
+  osds_t osds;
+  for (auto& peer : peers) {
+    osds.push_back(peer.first);
+  }
+  return seastar::map_reduce(std::move(osds),
+    [this](auto& osd) {
+      auto osdmap = service.get_map();
+      if (!osdmap->is_up(osd)) {
+        return remove_peer(osd).then([] {
+          return seastar::make_ready_future<osd_id_t>(-1);
+        });
+      } else if (peers[osd].epoch < osdmap->get_epoch()) {
+        return seastar::make_ready_future<osd_id_t>(osd);
+      } else {
+        return seastar::make_ready_future<osd_id_t>(-1);
+      }
+    }, osds_t{},
+    [this](osds_t&& extras, osd_id_t extra) {
+      if (extra >= 0) {
+        extras.push_back(extra);
+      }
+      return extras;
+    });
+}
+
+void Heartbeat::add_reporter_peers(int whoami)
+{
+  auto osdmap = service.get_map();
+  // include next and previous up osds to ensure we have a fully-connected set
+  set<int> want;
+  if (auto next = osdmap->get_next_up_osd_after(whoami); next >= 0) {
+    want.insert(next);
+  }
+  if (auto prev = osdmap->get_previous_up_osd_before(whoami); prev >= 0) {
+    want.insert(prev);
+  }
+  // make sure we have at least **min_down** osds coming from different
+  // subtree level (e.g., hosts) for fast failure detection.
+  auto min_down = local_conf().get_val<uint64_t>("mon_osd_min_down_reporters");
+  auto subtree = local_conf().get_val<string>("mon_osd_reporter_subtree_level");
+  osdmap->get_random_up_osds_by_subtree(
+    whoami, subtree, min_down, want, &want);
+  for (auto osd : want) {
+    add_peer(osd, osdmap->get_epoch());
+  }
+}
+
+seastar::future<> Heartbeat::update_peers(int whoami)
+{
+  const auto min_peers = static_cast<size_t>(
+    local_conf().get_val<int64_t>("osd_heartbeat_min_peers"));
+  return remove_down_peers().then([=](osds_t&& extra) {
+    add_reporter_peers(whoami);
+    // too many?
+    struct iteration_state {
+      osds_t::const_iterator where;
+      osds_t::const_iterator end;
+    };
+    return seastar::do_with(iteration_state{extra.begin(),extra.end()},
+      [=](iteration_state& s) {
+        return seastar::do_until(
+          [min_peers, &s, this] {
+            return peers.size() < min_peers || s.where == s.end; },
+          [&s, this] {
+            return remove_peer(*s.where); }
+        );
+    });
+  }).then([=] {
+    // or too few?
+    auto osdmap = service.get_map();
+    for (auto next = osdmap->get_next_up_osd_after(whoami);
+      peers.size() < min_peers && next >= 0 && next != whoami;
+      next = osdmap->get_next_up_osd_after(next)) {
+      add_peer(next, osdmap->get_epoch());
+    }
+    return seastar::now();
+  });
+}
+
+seastar::future<> Heartbeat::remove_peer(osd_id_t peer)
+{
+  auto found = peers.find(peer);
+  assert(found != peers.end());
+  logger().info("remove_peer({})", peer);
+  return seastar::when_all_succeed(found->second.con_front->close(),
+                                   found->second.con_back->close()).then(
+    [this, peer] {
+      peers.erase(peer);
+      return seastar::now();
+    });
+}
+
+seastar::future<> Heartbeat::ms_dispatch(ceph::net::ConnectionRef conn,
+                                         MessageRef m)
+{
+  logger().info("heartbeat: ms_dispatch {} from {}",
+                *m, m->get_source());
+  switch (m->get_type()) {
+  case CEPH_MSG_PING:
+    return handle_osd_ping(conn, boost::static_pointer_cast<MOSDPing>(m));
+  default:
+    return seastar::now();
+  }
+}
+
+seastar::future<> Heartbeat::handle_osd_ping(ceph::net::ConnectionRef conn,
+                                             Ref<MOSDPing> m)
+{
+  switch (m->op) {
+  case MOSDPing::PING:
+    return handle_ping(conn, m);
+  case MOSDPing::PING_REPLY:
+    return handle_reply(conn, m);
+  case MOSDPing::YOU_DIED:
+    return handle_you_died();
+  default:
+    return seastar::now();
+  }
+}
+
+seastar::future<> Heartbeat::handle_ping(ceph::net::ConnectionRef conn,
+                                         Ref<MOSDPing> m)
+{
+  auto min_message = static_cast<uint32_t>(
+    local_conf()->osd_heartbeat_min_size);
+  auto reply =
+    make_message<MOSDPing>(m->fsid,
+                           service.get_map()->get_epoch(),
+                           MOSDPing::PING_REPLY,
+                           m->stamp,
+                           min_message);
+  return conn->send(reply);
+}
+
+seastar::future<> Heartbeat::handle_reply(ceph::net::ConnectionRef conn,
+                                          Ref<MOSDPing> m)
+{
+  const osd_id_t from = m->get_source().num();
+  auto found = peers.find(from);
+  if (found == peers.end()) {
+    // stale reply
+    return seastar::now();
+  }
+  auto& peer = found->second;
+  auto ping = peer.ping_history.find(m->stamp);
+  if (ping == peer.ping_history.end()) {
+    // old replies, deprecated by newly sent pings.
+    return seastar::now();
+  }
+  const auto now = clock::now();
+  auto& unacked = ping->second.unacknowledged;
+  if (conn == peer.con_back) {
+    peer.last_rx_back = now;
+    unacked--;
+  } else if (conn == peer.con_front) {
+    peer.last_rx_front = now;
+    unacked--;
+  }
+  if (unacked == 0) {
+    peer.ping_history.erase(peer.ping_history.begin(), ++ping);
+  }
+  if (peer.is_healthy(now)) {
+    // cancel false reports
+    failure_queue.erase(from);
+    if (auto pending = failure_pending.find(from);
+        pending != failure_pending.end()) {
+      return send_still_alive(from, pending->second.addrs);
+    }
+  }
+  return seastar::now();
+}
+
+seastar::future<> Heartbeat::handle_you_died()
+{
+  // TODO: ask for newer osdmap
+  return seastar::now();
+}
+
+seastar::future<> Heartbeat::send_heartbeats()
+{
+  using peers_item_t = typename peers_map_t::value_type;
+  return seastar::parallel_for_each(peers,
+    [this](peers_item_t& item) {
+      const auto now = clock::now();
+      const auto deadline =
+        now + std::chrono::seconds(local_conf()->osd_heartbeat_grace);
+      auto& [peer, info] = item;
+      info.last_tx = now;
+      if (clock::is_zero(info.first_tx)) {
+        info.first_tx = now;
+      }
+      const utime_t sent_stamp{now};
+      auto [reply, added] = info.ping_history.emplace(sent_stamp,
+                                                      reply_t{deadline, 0});
+      std::vector<ceph::net::ConnectionRef> conns{info.con_front,
+                                                  info.con_back};
+      return seastar::parallel_for_each(std::move(conns),
+        [sent_stamp, &reply=reply->second, this] (auto con) {
+          if (con) {
+            auto min_message = static_cast<uint32_t>(
+              local_conf()->osd_heartbeat_min_size);
+            auto ping = make_message<MOSDPing>(monc.get_fsid(),
+                                               service.get_map()->get_epoch(),
+                                               MOSDPing::PING,
+                                               sent_stamp,
+                                               min_message);
+            return con->send(ping).then([&reply] {
+              reply.unacknowledged++;
+              return seastar::now();
+            });
+          } else {
+            return seastar::now();
+          }
+        });
+    });
+}
+
+seastar::future<> Heartbeat::send_failures()
+{
+  using failure_item_t = typename failure_queue_t::value_type;
+  return seastar::parallel_for_each(failure_queue,
+    [this](failure_item_t& failure_item) {
+      auto [osd, failed_since] = failure_item;
+      if (failure_pending.count(osd)) {
+        return seastar::now();
+      }
+      auto failed_for = chrono::duration_cast<chrono::seconds>(
+        clock::now() - failed_since).count();
+      auto osdmap = service.get_map();
+      auto failure_report =
+        make_message<MOSDFailure>(monc.get_fsid(),
+                                  osd,
+                                  osdmap->get_addrs(osd),
+                                  static_cast<int>(failed_for),
+                                  osdmap->get_epoch());
+      failure_pending.emplace(osd, failure_info_t{failed_since,
+                                                  osdmap->get_addrs(osd)});
+      return monc.send_message(failure_report);
+    }).then([this] {
+      failure_queue.clear();
+      return seastar::now();
+    });
+}
+
+seastar::future<> Heartbeat::send_still_alive(osd_id_t osd,
+                                              const entity_addrvec_t& addrs)
+{
+  auto still_alive = make_message<MOSDFailure>(monc.get_fsid(),
+                                               osd,
+                                               addrs,
+                                               0,
+                                               service.get_map()->get_epoch(),
+                                               MOSDFailure::FLAG_ALIVE);
+  return monc.send_message(still_alive).then([=] {
+    failure_pending.erase(osd);
+    return seastar::now();
+  });
+}
+
+bool Heartbeat::PeerInfo::is_unhealthy(clock::time_point now) const
+{
+  if (ping_history.empty()) {
+    // we haven't sent a ping yet or we have got all replies,
+    // in either way we are safe and healthy for now
+    return false;
+  } else {
+    auto oldest_ping = ping_history.begin();
+    return now > oldest_ping->second.deadline;
+  }
+}
+
+bool Heartbeat::PeerInfo::is_healthy(clock::time_point now) const
+{
+  if (con_front && clock::is_zero(last_rx_front)) {
+    return false;
+  }
+  if (con_back && clock::is_zero(last_rx_back)) {
+    return false;
+  }
+  // only declare to be healthy until we have received the first
+  // replies from both front/back connections
+  return !is_unhealthy(now);
+}
diff --git a/src/crimson/osd/heartbeat.h b/src/crimson/osd/heartbeat.h
new file mode 100644
index 00000000..b5eb0f7c
--- /dev/null
+++ b/src/crimson/osd/heartbeat.h
@@ -0,0 +1,121 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+
+#pragma once
+
+#include <cstdint>
+#include <seastar/core/future.hh>
+#include "common/ceph_time.h"
+#include "crimson/net/Dispatcher.h"
+#include "crimson/net/Fwd.h"
+
+class MOSDPing;
+class OSDMapService;
+
+namespace ceph::mon {
+  class Client;
+}
+
+template<typename Message> using Ref = boost::intrusive_ptr<Message>;
+
+class Heartbeat : public ceph::net::Dispatcher {
+public:
+  using osd_id_t = int;
+
+  Heartbeat(int whoami,
+	    uint32_t nonce,
+	    const OSDMapService& service,
+	    ceph::mon::Client& monc);
+
+  seastar::future<> start(entity_addrvec_t front,
+			  entity_addrvec_t back);
+  seastar::future<> stop();
+
+  seastar::future<> add_peer(osd_id_t peer, epoch_t epoch);
+  seastar::future<> update_peers(int whoami);
+  seastar::future<> remove_peer(osd_id_t peer);
+
+  seastar::future<> send_heartbeats();
+  seastar::future<> send_failures();
+
+  const entity_addrvec_t& get_front_addrs() const;
+  const entity_addrvec_t& get_back_addrs() const;
+
+  // Dispatcher methods
+  seastar::future<> ms_dispatch(ceph::net::ConnectionRef conn,
+				MessageRef m) override;
+
+private:
+  seastar::future<> handle_osd_ping(ceph::net::ConnectionRef conn,
+				    Ref<MOSDPing> m);
+  seastar::future<> handle_ping(ceph::net::ConnectionRef conn,
+				Ref<MOSDPing> m);
+  seastar::future<> handle_reply(ceph::net::ConnectionRef conn,
+				 Ref<MOSDPing> m);
+  seastar::future<> handle_you_died();
+
+  seastar::future<> send_still_alive(osd_id_t, const entity_addrvec_t&);
+
+  using osds_t = std::vector<osd_id_t>;
+  /// remove down OSDs
+  /// @return peers not needed in this epoch
+  seastar::future<osds_t> remove_down_peers();
+  /// add enough reporters for fast failure detection
+  void add_reporter_peers(int whoami);
+
+  seastar::future<> start_messenger(ceph::net::Messenger* msgr,
+				    const entity_addrvec_t& addrs);
+private:
+  const int whoami;
+  const uint32_t nonce;
+  ceph::net::Messenger* front_msgr = nullptr;
+  ceph::net::Messenger* back_msgr = nullptr;
+  const OSDMapService& service;
+  ceph::mon::Client& monc;
+
+  seastar::timer<seastar::lowres_clock> timer;
+  // use real_clock so it can be converted to utime_t
+  using clock = ceph::coarse_real_clock;
+
+  struct reply_t {
+    clock::time_point deadline;
+    // one sent over front conn, another sent over back conn
+    uint8_t unacknowledged = 0;
+  };
+  struct PeerInfo {
+    /// peer connection (front)
+    ceph::net::ConnectionRef con_front;
+    /// peer connection (back)
+    ceph::net::ConnectionRef con_back;
+    /// time we sent our first ping request
+    clock::time_point first_tx;
+    /// last time we sent a ping request
+    clock::time_point last_tx;
+    /// last time we got a ping reply on the front side
+    clock::time_point last_rx_front;
+    /// last time we got a ping reply on the back side
+    clock::time_point last_rx_back;
+    /// most recent epoch we wanted this peer
+    epoch_t epoch;
+    /// history of inflight pings, arranging by timestamp we sent
+    std::map<utime_t, reply_t> ping_history;
+
+    bool is_unhealthy(clock::time_point now) const;
+    bool is_healthy(clock::time_point now) const;
+  };
+  using peers_map_t = std::map<osd_id_t, PeerInfo>;
+  peers_map_t peers;
+
+  // osds which are considered failed
+  // osd_id => when was the last time that both front and back pings were acked
+  //           use for calculating how long the OSD has been unresponsive
+  using failure_queue_t = std::map<osd_id_t, clock::time_point>;
+  failure_queue_t failure_queue;
+  struct failure_info_t {
+    clock::time_point failed_since;
+    entity_addrvec_t addrs;
+  };
+  // osds we've reported to monior as failed ones, but they are not marked down
+  // yet
+  std::map<osd_id_t, failure_info_t> failure_pending;
+};
diff --git a/src/crimson/osd/main.cc b/src/crimson/osd/main.cc
new file mode 100644
index 00000000..04a0c97d
--- /dev/null
+++ b/src/crimson/osd/main.cc
@@ -0,0 +1,89 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:nil -*-
+// vim: ts=8 sw=2 smarttab
+
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <iostream>
+
+#include <seastar/core/app-template.hh>
+#include <seastar/core/thread.hh>
+
+#include "common/ceph_argparse.h"
+#include "crimson/common/config_proxy.h"
+
+#include "osd.h"
+
+using config_t = ceph::common::ConfigProxy;
+
+void usage(const char* prog) {
+  std::cout << "usage: " << prog << " -i <ID>" << std::endl;
+  generic_server_usage();
+}
+
+int main(int argc, char* argv[])
+{
+  std::vector<const char*> args{argv + 1, argv + argc};
+  if (ceph_argparse_need_usage(args)) {
+    usage(argv[0]);
+    return EXIT_SUCCESS;
+  }
+  std::string cluster;
+  std::string conf_file_list;
+  // ceph_argparse_early_args() could _exit(), while local_conf() won't ready
+  // until it's started. so do the boilerplate-settings parsing here.
+  auto init_params = ceph_argparse_early_args(args,
+                                              CEPH_ENTITY_TYPE_OSD,
+                                              &cluster,
+                                              &conf_file_list);
+  seastar::app_template app;
+  app.add_options()
+    ("mkfs", "create a [new] data directory");
+  seastar::sharded<OSD> osd;
+
+  using ceph::common::sharded_conf;
+  using ceph::common::sharded_perf_coll;
+  using ceph::common::local_conf;
+
+  args.insert(begin(args), argv[0]);
+  try {
+    return app.run_deprecated(args.size(), const_cast<char**>(args.data()), [&] {
+      auto& config = app.configuration();
+      seastar::engine().at_exit([] {
+        return sharded_conf().stop();
+      });
+      seastar::engine().at_exit([] {
+        return sharded_perf_coll().stop();
+      });
+      seastar::engine().at_exit([&] {
+       return osd.stop();
+      });
+      return sharded_conf().start(init_params.name, cluster).then([] {
+        return sharded_perf_coll().start();
+      }).then([&conf_file_list] {
+        return local_conf().parse_config_files(conf_file_list);
+      }).then([&] {
+        return osd.start_single(std::stoi(local_conf()->name.get_id()),
+                                static_cast<uint32_t>(getpid()));
+      }).then([&osd, mkfs = config.count("mkfs")] {
+        if (mkfs) {
+          return osd.invoke_on(0, &OSD::mkfs,
+                               local_conf().get_val<uuid_d>("fsid"));
+        } else {
+          return osd.invoke_on(0, &OSD::start);
+        }
+      });
+    });
+  } catch (...) {
+    seastar::fprint(std::cerr, "FATAL: Exception during startup, aborting: %s\n", std::current_exception());
+    return EXIT_FAILURE;
+  }
+}
+
+/*
+ * Local Variables:
+ * compile-command: "make -j4 \
+ * -C ../../../build \
+ * crimson-osd"
+ * End:
+ */
diff --git a/src/crimson/osd/osd.cc b/src/crimson/osd/osd.cc
new file mode 100644
index 00000000..bdb1642e
--- /dev/null
+++ b/src/crimson/osd/osd.cc
@@ -0,0 +1,658 @@
+#include "osd.h"
+
+#include <boost/range/join.hpp>
+#include <boost/smart_ptr/make_local_shared.hpp>
+
+#include "common/pick_address.h"
+#include "messages/MOSDBeacon.h"
+#include "messages/MOSDBoot.h"
+#include "messages/MOSDMap.h"
+#include "crimson/net/Connection.h"
+#include "crimson/net/Messenger.h"
+#include "crimson/os/cyan_collection.h"
+#include "crimson/os/cyan_object.h"
+#include "crimson/os/cyan_store.h"
+#include "crimson/os/Transaction.h"
+#include "crimson/osd/heartbeat.h"
+#include "crimson/osd/osd_meta.h"
+#include "crimson/osd/pg.h"
+#include "crimson/osd/pg_meta.h"
+
+namespace {
+  seastar::logger& logger() {
+    return ceph::get_logger(ceph_subsys_osd);
+  }
+
+  template<typename Message, typename... Args>
+  Ref<Message> make_message(Args&&... args)
+  {
+    return {new Message{std::forward<Args>(args)...}, false};
+  }
+  static constexpr int TICK_INTERVAL = 1;
+}
+
+using ceph::common::local_conf;
+using ceph::os::CyanStore;
+
+OSD::OSD(int id, uint32_t nonce)
+  : whoami{id},
+    nonce{nonce},
+    beacon_timer{[this] { send_beacon(); }},
+    heartbeat_timer{[this] { update_heartbeat_peers(); }}
+{
+  osdmaps[0] = boost::make_local_shared<OSDMap>();
+}
+
+OSD::~OSD() = default;
+
+namespace {
+// Initial features in new superblock.
+// Features here are also automatically upgraded
+CompatSet get_osd_initial_compat_set()
+{
+  CompatSet::FeatureSet ceph_osd_feature_compat;
+  CompatSet::FeatureSet ceph_osd_feature_ro_compat;
+  CompatSet::FeatureSet ceph_osd_feature_incompat;
+  ceph_osd_feature_incompat.insert(CEPH_OSD_FEATURE_INCOMPAT_BASE);
+  ceph_osd_feature_incompat.insert(CEPH_OSD_FEATURE_INCOMPAT_PGINFO);
+  ceph_osd_feature_incompat.insert(CEPH_OSD_FEATURE_INCOMPAT_OLOC);
+  ceph_osd_feature_incompat.insert(CEPH_OSD_FEATURE_INCOMPAT_LEC);
+  ceph_osd_feature_incompat.insert(CEPH_OSD_FEATURE_INCOMPAT_CATEGORIES);
+  ceph_osd_feature_incompat.insert(CEPH_OSD_FEATURE_INCOMPAT_HOBJECTPOOL);
+  ceph_osd_feature_incompat.insert(CEPH_OSD_FEATURE_INCOMPAT_BIGINFO);
+  ceph_osd_feature_incompat.insert(CEPH_OSD_FEATURE_INCOMPAT_LEVELDBINFO);
+  ceph_osd_feature_incompat.insert(CEPH_OSD_FEATURE_INCOMPAT_LEVELDBLOG);
+  ceph_osd_feature_incompat.insert(CEPH_OSD_FEATURE_INCOMPAT_SNAPMAPPER);
+  ceph_osd_feature_incompat.insert(CEPH_OSD_FEATURE_INCOMPAT_HINTS);
+  ceph_osd_feature_incompat.insert(CEPH_OSD_FEATURE_INCOMPAT_PGMETA);
+  ceph_osd_feature_incompat.insert(CEPH_OSD_FEATURE_INCOMPAT_MISSING);
+  ceph_osd_feature_incompat.insert(CEPH_OSD_FEATURE_INCOMPAT_FASTINFO);
+  ceph_osd_feature_incompat.insert(CEPH_OSD_FEATURE_INCOMPAT_RECOVERY_DELETES);
+  return CompatSet(ceph_osd_feature_compat,
+                   ceph_osd_feature_ro_compat,
+                   ceph_osd_feature_incompat);
+}
+}
+
+seastar::future<> OSD::mkfs(uuid_d cluster_fsid)
+{
+  const auto data_path = local_conf().get_val<std::string>("osd_data");
+  store = std::make_unique<ceph::os::CyanStore>(data_path);
+  uuid_d osd_fsid;
+  osd_fsid.generate_random();
+  return store->mkfs(osd_fsid).then([this] {
+    return store->mount();
+  }).then([cluster_fsid, osd_fsid, this] {
+    superblock.cluster_fsid = cluster_fsid;
+    superblock.osd_fsid = osd_fsid;
+    superblock.whoami = whoami;
+    superblock.compat_features = get_osd_initial_compat_set();
+
+    meta_coll = make_unique<OSDMeta>(
+      store->create_new_collection(coll_t::meta()), store.get());
+    ceph::os::Transaction t;
+    meta_coll->create(t);
+    meta_coll->store_superblock(t, superblock);
+    return store->do_transaction(meta_coll->collection(), std::move(t));
+  }).then([cluster_fsid, this] {
+    store->write_meta("ceph_fsid", cluster_fsid.to_string());
+    store->write_meta("whoami", std::to_string(whoami));
+    return seastar::now();
+  });
+}
+
+namespace {
+  entity_addrvec_t pick_addresses(int what) {
+    entity_addrvec_t addrs;
+    CephContext cct;
+    if (int r = ::pick_addresses(&cct, what, &addrs, -1); r < 0) {
+      throw std::runtime_error("failed to pick address");
+    }
+    // TODO: v2: ::pick_addresses() returns v2 addresses, but crimson-msgr does
+    // not support v2 yet. remove following set_type() once v2 support is ready.
+    for (auto addr : addrs.v) {
+      addr.set_type(addr.TYPE_LEGACY);
+      logger().info("picked address {}", addr);
+    }
+    return addrs;
+  }
+  std::pair<entity_addrvec_t, bool>
+  replace_unknown_addrs(entity_addrvec_t maybe_unknowns,
+                        const entity_addrvec_t& knowns) {
+    bool changed = false;
+    auto maybe_replace = [&](entity_addr_t addr) {
+      if (!addr.is_blank_ip()) {
+        return addr;
+      }
+      for (auto& b : knowns.v) {
+        if (addr.get_family() == b.get_family()) {
+          auto a = b;
+          a.set_nonce(addr.get_nonce());
+          a.set_type(addr.get_type());
+          a.set_port(addr.get_port());
+          changed = true;
+          return a;
+        }
+      }
+      throw std::runtime_error("failed to replace unknown address");
+    };
+    entity_addrvec_t replaced;
+    std::transform(maybe_unknowns.v.begin(),
+                   maybe_unknowns.v.end(),
+                   std::back_inserter(replaced.v),
+                   maybe_replace);
+    return {replaced, changed};
+  }
+}
+
+seastar::future<> OSD::start()
+{
+  logger().info("start");
+
+  return seastar::when_all_succeed(
+    ceph::net::Messenger::create(entity_name_t::OSD(whoami),
+                                 "cluster",
+                                 nonce,
+                                 seastar::engine().cpu_id())
+      .then([this] (auto msgr) { cluster_msgr = msgr; }),
+    ceph::net::Messenger::create(entity_name_t::OSD(whoami),
+                                 "client",
+                                 nonce,
+                                 seastar::engine().cpu_id())
+      .then([this] (auto msgr) { public_msgr = msgr; }))
+  .then([this] {
+    monc.reset(new ceph::mon::Client{*public_msgr});
+    heartbeat.reset(new Heartbeat{whoami, nonce, *this, *monc});
+
+    for (auto msgr : {cluster_msgr, public_msgr}) {
+      if (local_conf()->ms_crc_data) {
+        msgr->set_crc_data();
+      }
+      if (local_conf()->ms_crc_header) {
+        msgr->set_crc_header();
+      }
+    }
+    dispatchers.push_front(this);
+    dispatchers.push_front(monc.get());
+
+    const auto data_path = local_conf().get_val<std::string>("osd_data");
+    store = std::make_unique<ceph::os::CyanStore>(data_path);
+    return store->mount();
+  }).then([this] {
+    meta_coll = make_unique<OSDMeta>(store->open_collection(coll_t::meta()),
+                                     store.get());
+    return meta_coll->load_superblock();
+  }).then([this](OSDSuperblock&& sb) {
+    superblock = std::move(sb);
+    return get_map(superblock.current_epoch);
+  }).then([this](cached_map_t&& map) {
+    osdmap = std::move(map);
+    return load_pgs();
+  }).then([this] {
+    return seastar::when_all_succeed(
+      cluster_msgr->try_bind(pick_addresses(CEPH_PICK_ADDRESS_CLUSTER),
+                             local_conf()->ms_bind_port_min,
+                             local_conf()->ms_bind_port_max)
+        .then([this] { return cluster_msgr->start(&dispatchers); }),
+      public_msgr->try_bind(pick_addresses(CEPH_PICK_ADDRESS_PUBLIC),
+                            local_conf()->ms_bind_port_min,
+                            local_conf()->ms_bind_port_max)
+        .then([this] { return public_msgr->start(&dispatchers); }));
+  }).then([this] {
+    return monc->start();
+  }).then([this] {
+    monc->sub_want("osd_pg_creates", last_pg_create_epoch, 0);
+    monc->sub_want("mgrmap", 0, 0);
+    monc->sub_want("osdmap", 0, 0);
+    return monc->renew_subs();
+  }).then([this] {
+    if (auto [addrs, changed] =
+        replace_unknown_addrs(cluster_msgr->get_myaddrs(),
+                              public_msgr->get_myaddrs()); changed) {
+      cluster_msgr->set_myaddrs(addrs);
+    }
+    return heartbeat->start(public_msgr->get_myaddrs(),
+                            cluster_msgr->get_myaddrs());
+  }).then([this] {
+    return start_boot();
+  });
+}
+
+seastar::future<> OSD::start_boot()
+{
+  state.set_preboot();
+  return monc->get_version("osdmap").then([this](version_t newest, version_t oldest) {
+    return _preboot(oldest, newest);
+  });
+}
+
+seastar::future<> OSD::_preboot(version_t oldest, version_t newest)
+{
+  logger().info("osd.{}: _preboot", whoami);
+  if (osdmap->get_epoch() == 0) {
+    logger().warn("waiting for initial osdmap");
+  } else if (osdmap->is_destroyed(whoami)) {
+    logger().warn("osdmap says I am destroyed");
+    // provide a small margin so we don't livelock seeing if we
+    // un-destroyed ourselves.
+    if (osdmap->get_epoch() > newest - 1) {
+      throw std::runtime_error("i am destroyed");
+    }
+  } else if (osdmap->is_noup(whoami)) {
+    logger().warn("osdmap NOUP flag is set, waiting for it to clear");
+  } else if (!osdmap->test_flag(CEPH_OSDMAP_SORTBITWISE)) {
+    logger().error("osdmap SORTBITWISE OSDMap flag is NOT set; please set it");
+  } else if (osdmap->require_osd_release < CEPH_RELEASE_LUMINOUS) {
+    logger().error("osdmap require_osd_release < luminous; please upgrade to luminous");
+  } else if (false) {
+    // TODO: update mon if current fullness state is different from osdmap
+  } else if (version_t n = local_conf()->osd_map_message_max;
+             osdmap->get_epoch() >= oldest - 1 &&
+             osdmap->get_epoch() + n > newest) {
+    return _send_boot();
+  }
+  // get all the latest maps
+  if (osdmap->get_epoch() + 1 >= oldest) {
+    return osdmap_subscribe(osdmap->get_epoch() + 1, false);
+  } else {
+    return osdmap_subscribe(oldest - 1, true);
+  }
+}
+
+seastar::future<> OSD::_send_boot()
+{
+  state.set_booting();
+
+  logger().info("hb_back_msgr: {}", heartbeat->get_back_addrs());
+  logger().info("hb_front_msgr: {}", heartbeat->get_front_addrs());
+  logger().info("cluster_msgr: {}", cluster_msgr->get_myaddr());
+  auto m = make_message<MOSDBoot>(superblock,
+                                  osdmap->get_epoch(),
+                                  osdmap->get_epoch(),
+                                  heartbeat->get_back_addrs(),
+                                  heartbeat->get_front_addrs(),
+                                  cluster_msgr->get_myaddrs(),
+                                  CEPH_FEATURES_ALL);
+  return monc->send_message(m);
+}
+
+seastar::future<> OSD::stop()
+{
+  // see also OSD::shutdown()
+  state.set_stopping();
+  return gate.close().then([this] {
+    return heartbeat->stop();
+  }).then([this] {
+    return monc->stop();
+  }).then([this] {
+    return public_msgr->shutdown();
+  }).then([this] {
+    return cluster_msgr->shutdown();
+  });
+}
+
+seastar::future<> OSD::load_pgs()
+{
+  return seastar::parallel_for_each(store->list_collections(),
+    [this](auto coll) {
+      spg_t pgid;
+      if (coll.is_pg(&pgid)) {
+        return load_pg(pgid).then([pgid, this](auto&& pg) {
+          logger().info("load_pgs: loaded {}", pgid);
+          pgs.emplace(pgid, std::move(pg));
+          return seastar::now();
+        });
+      } else if (coll.is_temp(&pgid)) {
+        // TODO: remove the collection
+        return seastar::now();
+      } else {
+        logger().warn("ignoring unrecognized collection: {}", coll);
+        return seastar::now();
+      }
+    });
+}
+
+seastar::future<Ref<PG>> OSD::load_pg(spg_t pgid)
+{
+  using ec_profile_t = map<string,string>;
+  return PGMeta{store.get(), pgid}.get_epoch().then([this](epoch_t e) {
+    return get_map(e);
+  }).then([pgid, this] (auto&& create_map) {
+    if (create_map->have_pg_pool(pgid.pool())) {
+      pg_pool_t pi = *create_map->get_pg_pool(pgid.pool());
+      string name = create_map->get_pool_name(pgid.pool());
+      ec_profile_t ec_profile;
+      if (pi.is_erasure()) {
+        ec_profile = create_map->get_erasure_code_profile(pi.erasure_code_profile);
+      }
+      return seastar::make_ready_future<pg_pool_t,
+                                        string,
+                                        ec_profile_t>(std::move(pi),
+                                                      std::move(name),
+                                                      std::move(ec_profile));
+    } else {
+      // pool was deleted; grab final pg_pool_t off disk.
+      return meta_coll->load_final_pool_info(pgid.pool());
+    }
+  }).then([this](pg_pool_t&& pool, string&& name, ec_profile_t&& ec_profile) {
+    Ref<PG> pg{new PG{std::move(pool),
+                      std::move(name),
+                      std::move(ec_profile)}};
+    return seastar::make_ready_future<Ref<PG>>(std::move(pg));
+  });
+}
+
+seastar::future<> OSD::ms_dispatch(ceph::net::ConnectionRef conn, MessageRef m)
+{
+  logger().info("ms_dispatch {}", *m);
+  if (state.is_stopping()) {
+    return seastar::now();
+  }
+
+  switch (m->get_type()) {
+  case CEPH_MSG_OSD_MAP:
+    return handle_osd_map(conn, boost::static_pointer_cast<MOSDMap>(m));
+  default:
+    return seastar::now();
+  }
+}
+
+seastar::future<> OSD::ms_handle_connect(ceph::net::ConnectionRef conn)
+{
+  if (conn->get_peer_type() != CEPH_ENTITY_TYPE_MON) {
+    return seastar::now();
+  } else {
+    return seastar::now();
+  }
+}
+
+seastar::future<> OSD::ms_handle_reset(ceph::net::ConnectionRef conn)
+{
+  // TODO: cleanup the session attached to this connection
+  logger().warn("ms_handle_reset");
+  return seastar::now();
+}
+
+seastar::future<> OSD::ms_handle_remote_reset(ceph::net::ConnectionRef conn)
+{
+  logger().warn("ms_handle_remote_reset");
+  return seastar::now();
+}
+
+OSD::cached_map_t OSD::get_map() const
+{
+  return osdmap;
+}
+
+seastar::future<OSD::cached_map_t> OSD::get_map(epoch_t e)
+{
+  // TODO: use LRU cache for managing osdmap, fallback to disk if we have to
+  if (auto found = osdmaps.find(e); found) {
+    return seastar::make_ready_future<cached_map_t>(std::move(found));
+  } else {
+    return load_map_bl(e).then([e, this](bufferlist bl) {
+      auto osdmap = std::make_unique<OSDMap>();
+      osdmap->decode(bl);
+      return seastar::make_ready_future<cached_map_t>(
+        osdmaps.insert(e, std::move(osdmap)));
+    });
+  }
+}
+
+void OSD::store_map_bl(ceph::os::Transaction& t,
+                       epoch_t e, bufferlist&& bl)
+{
+  meta_coll->store_map(t, e, bl);
+  map_bl_cache.insert(e, std::move(bl));
+}
+
+seastar::future<bufferlist> OSD::load_map_bl(epoch_t e)
+{
+  if (std::optional<bufferlist> found = map_bl_cache.find(e); found) {
+    return seastar::make_ready_future<bufferlist>(*found);
+  } else {
+    return meta_coll->load_map(e);
+  }
+}
+
+seastar::future<> OSD::store_maps(ceph::os::Transaction& t,
+                                  epoch_t start, Ref<MOSDMap> m)
+{
+  return seastar::do_for_each(boost::counting_iterator<epoch_t>(start),
+                              boost::counting_iterator<epoch_t>(m->get_last() + 1),
+                              [&t, m, this](epoch_t e) {
+    if (auto p = m->maps.find(e); p != m->maps.end()) {
+      auto o = std::make_unique<OSDMap>();
+      o->decode(p->second);
+      logger().info("store_maps osdmap.{}", e);
+      store_map_bl(t, e, std::move(std::move(p->second)));
+      osdmaps.insert(e, std::move(o));
+      return seastar::now();
+    } else if (auto p = m->incremental_maps.find(e);
+               p != m->incremental_maps.end()) {
+      OSDMap::Incremental inc;
+      auto i = p->second.cbegin();
+      inc.decode(i);
+      return load_map_bl(e - 1)
+        .then([&t, e, inc=std::move(inc), this](bufferlist bl) {
+          auto o = std::make_unique<OSDMap>();
+          o->decode(bl);
+          o->apply_incremental(inc);
+          bufferlist fbl;
+          o->encode(fbl, inc.encode_features | CEPH_FEATURE_RESERVED);
+          store_map_bl(t, e, std::move(fbl));
+          osdmaps.insert(e, std::move(o));
+          return seastar::now();
+      });
+    } else {
+      logger().error("MOSDMap lied about what maps it had?");
+      return seastar::now();
+    }
+  });
+}
+
+seastar::future<> OSD::osdmap_subscribe(version_t epoch, bool force_request)
+{
+  logger().info("{}({})", __func__, epoch);
+  if (monc->sub_want_increment("osdmap", epoch, CEPH_SUBSCRIBE_ONETIME) ||
+      force_request) {
+    return monc->renew_subs();
+  } else {
+    return seastar::now();
+  }
+}
+
+seastar::future<> OSD::handle_osd_map(ceph::net::ConnectionRef conn,
+                                      Ref<MOSDMap> m)
+{
+  logger().info("handle_osd_map {}", *m);
+  if (m->fsid != superblock.cluster_fsid) {
+    logger().warn("fsid mismatched");
+    return seastar::now();
+  }
+  if (state.is_initializing()) {
+    logger().warn("i am still initializing");
+    return seastar::now();
+  }
+
+  const auto first = m->get_first();
+  const auto last = m->get_last();
+
+  // make sure there is something new, here, before we bother flushing
+  // the queues and such
+  if (last <= superblock.newest_map) {
+    return seastar::now();
+  }
+  // missing some?
+  bool skip_maps = false;
+  epoch_t start = superblock.newest_map + 1;
+  if (first > start) {
+    logger().info("handle_osd_map message skips epochs {}..{}",
+                  start, first - 1);
+    if (m->oldest_map <= start) {
+      return osdmap_subscribe(start, false);
+    }
+    // always try to get the full range of maps--as many as we can.  this
+    //  1- is good to have
+    //  2- is at present the only way to ensure that we get a *full* map as
+    //     the first map!
+    if (m->oldest_map < first) {
+      return osdmap_subscribe(m->oldest_map - 1, true);
+    }
+    skip_maps = true;
+    start = first;
+  }
+
+  return seastar::do_with(ceph::os::Transaction{},
+                          [=](auto& t) {
+    return store_maps(t, start, m).then([=, &t] {
+      // even if this map isn't from a mon, we may have satisfied our subscription
+      monc->sub_got("osdmap", last);
+      if (!superblock.oldest_map || skip_maps) {
+        superblock.oldest_map = first;
+      }
+      superblock.newest_map = last;
+      superblock.current_epoch = last;
+
+      // note in the superblock that we were clean thru the prior epoch
+      if (boot_epoch && boot_epoch >= superblock.mounted) {
+        superblock.mounted = boot_epoch;
+        superblock.clean_thru = last;
+      }
+      meta_coll->store_superblock(t, superblock);
+      return store->do_transaction(meta_coll->collection(), std::move(t));
+    });
+  }).then([=] {
+    // TODO: write to superblock and commit the transaction
+    return committed_osd_maps(start, last, m);
+  });
+}
+
+seastar::future<> OSD::committed_osd_maps(version_t first,
+                                          version_t last,
+                                          Ref<MOSDMap> m)
+{
+  logger().info("osd.{}: committed_osd_maps({}, {})", whoami, first, last);
+  // advance through the new maps
+  return seastar::parallel_for_each(boost::irange(first, last + 1),
+                                    [this](epoch_t cur) {
+    return get_map(cur).then([this](cached_map_t&& o) {
+      osdmap = std::move(o);
+      if (up_epoch != 0 &&
+          osdmap->is_up(whoami) &&
+          osdmap->get_addrs(whoami) == public_msgr->get_myaddrs()) {
+        up_epoch = osdmap->get_epoch();
+        if (!boot_epoch) {
+          boot_epoch = osdmap->get_epoch();
+        }
+      }
+    });
+  }).then([m, this] {
+    if (osdmap->is_up(whoami) &&
+        osdmap->get_addrs(whoami) == public_msgr->get_myaddrs() &&
+        bind_epoch < osdmap->get_up_from(whoami)) {
+      if (state.is_booting()) {
+        logger().info("osd.{}: activating...", whoami);
+        state.set_active();
+        beacon_timer.arm_periodic(
+          std::chrono::seconds(local_conf()->osd_beacon_report_interval));
+        heartbeat_timer.arm_periodic(
+          std::chrono::seconds(TICK_INTERVAL));
+      }
+    }
+
+    if (state.is_active()) {
+      logger().info("osd.{}: now active", whoami);
+      if (!osdmap->exists(whoami)) {
+        return shutdown();
+      }
+      if (should_restart()) {
+        return restart();
+      } else {
+        return seastar::now();
+      }
+    } else if (state.is_preboot()) {
+      logger().info("osd.{}: now preboot", whoami);
+
+      if (m->get_source().is_mon()) {
+        return _preboot(m->oldest_map, m->newest_map);
+      } else {
+        logger().info("osd.{}: start_boot", whoami);
+        return start_boot();
+      }
+    } else {
+      logger().info("osd.{}: now {}", whoami, state);
+      // XXX
+      return seastar::now();
+    }
+  });
+}
+
+bool OSD::should_restart() const
+{
+  if (!osdmap->is_up(whoami)) {
+    logger().info("map e {} marked osd.{} down",
+                  osdmap->get_epoch(), whoami);
+    return true;
+  } else if (osdmap->get_addrs(whoami) != public_msgr->get_myaddrs()) {
+    logger().error("map e {} had wrong client addr ({} != my {})",
+                   osdmap->get_epoch(),
+                   osdmap->get_addrs(whoami),
+                   public_msgr->get_myaddrs());
+    return true;
+  } else if (osdmap->get_cluster_addrs(whoami) != cluster_msgr->get_myaddrs()) {
+    logger().error("map e {} had wrong cluster addr ({} != my {})",
+                   osdmap->get_epoch(),
+                   osdmap->get_cluster_addrs(whoami),
+                   cluster_msgr->get_myaddrs());
+    return true;
+  } else {
+    return false;
+  }
+}
+
+seastar::future<> OSD::restart()
+{
+  up_epoch = 0;
+  bind_epoch = osdmap->get_epoch();
+  // TODO: promote to shutdown if being marked down for multiple times
+  // rebind messengers
+  return start_boot();
+}
+
+seastar::future<> OSD::shutdown()
+{
+  // TODO
+  superblock.mounted = boot_epoch;
+  superblock.clean_thru = osdmap->get_epoch();
+  return seastar::now();
+}
+
+seastar::future<> OSD::send_beacon()
+{
+  // FIXME: min lec should be calculated from pg_stat
+  //        and should set m->pgs
+  epoch_t min_last_epoch_clean = osdmap->get_epoch();
+  auto m = make_message<MOSDBeacon>(osdmap->get_epoch(),
+                                    min_last_epoch_clean);
+  return monc->send_message(m);
+}
+
+void OSD::update_heartbeat_peers()
+{
+  if (!state.is_active()) {
+    return;
+  }
+  for (auto& pg : pgs) {
+    vector<int> up, acting;
+    osdmap->pg_to_up_acting_osds(pg.first.pgid,
+                                 &up, nullptr,
+                                 &acting, nullptr);
+    for (auto osd : boost::join(up, acting)) {
+      if (osd != CRUSH_ITEM_NONE) {
+        heartbeat->add_peer(osd, osdmap->get_epoch());
+      }
+    }
+  }
+  heartbeat->update_peers(whoami);
+}
diff --git a/src/crimson/osd/osd.h b/src/crimson/osd/osd.h
new file mode 100644
index 00000000..c5aff5e2
--- /dev/null
+++ b/src/crimson/osd/osd.h
@@ -0,0 +1,125 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+
+#pragma once
+
+#include <map>
+#include <seastar/core/future.hh>
+#include <seastar/core/gate.hh>
+#include <seastar/core/shared_ptr.hh>
+#include <seastar/core/timer.hh>
+
+#include "crimson/common/simple_lru.h"
+#include "crimson/common/shared_lru.h"
+#include "crimson/mon/MonClient.h"
+#include "crimson/net/Dispatcher.h"
+#include "crimson/osd/chained_dispatchers.h"
+#include "crimson/osd/osdmap_service.h"
+#include "crimson/osd/state.h"
+
+#include "osd/OSDMap.h"
+
+class MOSDMap;
+class OSDMap;
+class OSDMeta;
+class PG;
+class Heartbeat;
+
+namespace ceph::net {
+  class Messenger;
+}
+
+namespace ceph::os {
+  class CyanStore;
+  struct Collection;
+  class Transaction;
+}
+
+template<typename T> using Ref = boost::intrusive_ptr<T>;
+
+class OSD : public ceph::net::Dispatcher,
+	    private OSDMapService {
+  seastar::gate gate;
+  const int whoami;
+  const uint32_t nonce;
+  seastar::timer<seastar::lowres_clock> beacon_timer;
+  // talk with osd
+  ceph::net::Messenger* cluster_msgr = nullptr;
+  // talk with client/mon/mgr
+  ceph::net::Messenger* public_msgr = nullptr;
+  ChainedDispatchers dispatchers;
+  std::unique_ptr<ceph::mon::Client> monc;
+
+  std::unique_ptr<Heartbeat> heartbeat;
+  seastar::timer<seastar::lowres_clock> heartbeat_timer;
+
+  SharedLRU<epoch_t, OSDMap> osdmaps;
+  SimpleLRU<epoch_t, bufferlist, false> map_bl_cache;
+  cached_map_t osdmap;
+  // TODO: use a wrapper for ObjectStore
+  std::unique_ptr<ceph::os::CyanStore> store;
+  std::unique_ptr<OSDMeta> meta_coll;
+
+  std::unordered_map<spg_t, Ref<PG>> pgs;
+  OSDState state;
+
+  /// _first_ epoch we were marked up (after this process started)
+  epoch_t boot_epoch = 0;
+  /// _most_recent_ epoch we were marked up
+  epoch_t up_epoch = 0;
+  //< epoch we last did a bind to new ip:ports
+  epoch_t bind_epoch = 0;
+  //< since when there is no more pending pg creates from mon
+  epoch_t last_pg_create_epoch = 0;
+
+  OSDSuperblock superblock;
+
+  // Dispatcher methods
+  seastar::future<> ms_dispatch(ceph::net::ConnectionRef conn, MessageRef m) override;
+  seastar::future<> ms_handle_connect(ceph::net::ConnectionRef conn) override;
+  seastar::future<> ms_handle_reset(ceph::net::ConnectionRef conn) override;
+  seastar::future<> ms_handle_remote_reset(ceph::net::ConnectionRef conn) override;
+
+public:
+  OSD(int id, uint32_t nonce);
+  ~OSD() override;
+
+  seastar::future<> mkfs(uuid_d fsid);
+
+  seastar::future<> start();
+  seastar::future<> stop();
+
+private:
+  seastar::future<> start_boot();
+  seastar::future<> _preboot(version_t oldest_osdmap, version_t newest_osdmap);
+  seastar::future<> _send_boot();
+
+  seastar::future<Ref<PG>> load_pg(spg_t pgid);
+  seastar::future<> load_pgs();
+
+  // OSDMapService methods
+  seastar::future<cached_map_t> get_map(epoch_t e) override;
+  cached_map_t get_map() const override;
+
+  seastar::future<bufferlist> load_map_bl(epoch_t e);
+  void store_map_bl(ceph::os::Transaction& t,
+                    epoch_t e, bufferlist&& bl);
+  seastar::future<> store_maps(ceph::os::Transaction& t,
+                               epoch_t start, Ref<MOSDMap> m);
+  seastar::future<> osdmap_subscribe(version_t epoch, bool force_request);
+
+  void write_superblock(ceph::os::Transaction& t);
+  seastar::future<> read_superblock();
+
+  seastar::future<> handle_osd_map(ceph::net::ConnectionRef conn,
+                                   Ref<MOSDMap> m);
+  seastar::future<> committed_osd_maps(version_t first,
+                                       version_t last,
+                                       Ref<MOSDMap> m);
+  bool should_restart() const;
+  seastar::future<> restart();
+  seastar::future<> shutdown();
+
+  seastar::future<> send_beacon();
+  void update_heartbeat_peers();
+};
diff --git a/src/crimson/osd/osd_meta.cc b/src/crimson/osd/osd_meta.cc
new file mode 100644
index 00000000..6eb225fe
--- /dev/null
+++ b/src/crimson/osd/osd_meta.cc
@@ -0,0 +1,80 @@
+#include "osd_meta.h"
+
+#include "crimson/os/cyan_collection.h"
+#include "crimson/os/cyan_store.h"
+#include "crimson/os/Transaction.h"
+
+void OSDMeta::create(ceph::os::Transaction& t)
+{
+  t.create_collection(coll->cid, 0);
+}
+
+void OSDMeta::store_map(ceph::os::Transaction& t,
+                        epoch_t e, const bufferlist& m)
+{
+  t.write(coll->cid, osdmap_oid(e), 0, m.length(), m);
+}
+
+seastar::future<bufferlist> OSDMeta::load_map(epoch_t e)
+{
+  return store->read(coll,
+                     osdmap_oid(e), 0, 0,
+                     CEPH_OSD_OP_FLAG_FADVISE_WILLNEED);
+}
+
+void OSDMeta::store_superblock(ceph::os::Transaction& t,
+                               const OSDSuperblock& superblock)
+{
+  bufferlist bl;
+  encode(superblock, bl);
+  t.write(coll->cid, superblock_oid(), 0, bl.length(), bl);
+}
+
+seastar::future<OSDSuperblock> OSDMeta::load_superblock()
+{
+  return store->read(coll, superblock_oid(), 0, 0)
+    .then([this] (bufferlist&& bl) {
+      auto p = bl.cbegin();
+      OSDSuperblock superblock;
+      decode(superblock, p);
+      return seastar::make_ready_future<OSDSuperblock>(std::move(superblock));
+  });
+}
+
+seastar::future<pg_pool_t,
+                std::string,
+                OSDMeta::ec_profile_t>
+OSDMeta::load_final_pool_info(int64_t pool) {
+  return store->read(coll, final_pool_info_oid(pool),
+                     0, 0).then([this] (bufferlist&& bl) {
+    auto p = bl.cbegin();
+    pg_pool_t pi;
+    string name;
+    ec_profile_t ec_profile;
+    decode(pi, p);
+    decode(name, p);
+    decode(ec_profile, p);
+    return seastar::make_ready_future<pg_pool_t,
+                                      string,
+                                      ec_profile_t>(std::move(pi),
+                                                    std::move(name),
+                                                    std::move(ec_profile));
+  });
+}
+
+ghobject_t OSDMeta::osdmap_oid(epoch_t epoch)
+{
+  string name = fmt::format("osdmap.{}", epoch);
+  return ghobject_t(hobject_t(sobject_t(object_t(name), 0)));
+}
+
+ghobject_t OSDMeta::final_pool_info_oid(int64_t pool)
+{
+  string name = fmt::format("final_pool_{}", pool);
+  return ghobject_t(hobject_t(sobject_t(object_t(name), CEPH_NOSNAP)));
+}
+
+ghobject_t OSDMeta::superblock_oid()
+{
+  return ghobject_t(hobject_t(sobject_t(object_t("osd_superblock"), 0)));
+}
diff --git a/src/crimson/osd/osd_meta.h b/src/crimson/osd/osd_meta.h
new file mode 100644
index 00000000..936d9548
--- /dev/null
+++ b/src/crimson/osd/osd_meta.h
@@ -0,0 +1,53 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+
+#pragma once
+
+#include <map>
+#include <string>
+#include <seastar/core/future.hh>
+#include "osd/osd_types.h"
+
+namespace ceph::os {
+  class CyanStore;
+  class Collection;
+  class Transaction;
+}
+
+/// metadata shared across PGs, or put in another way,
+/// metadata not specific to certain PGs.
+class OSDMeta {
+  template<typename T> using Ref = boost::intrusive_ptr<T>;
+
+  ceph::os::CyanStore* store;
+  Ref<ceph::os::Collection> coll;
+
+public:
+  OSDMeta(Ref<ceph::os::Collection> coll,
+          ceph::os::CyanStore* store)
+    : store{store}, coll{coll}
+  {}
+
+
+  auto collection() {
+    return coll;
+  }
+  void create(ceph::os::Transaction& t);
+
+  void store_map(ceph::os::Transaction& t,
+                 epoch_t e, const bufferlist& m);
+  seastar::future<bufferlist> load_map(epoch_t e);
+
+  void store_superblock(ceph::os::Transaction& t,
+                        const OSDSuperblock& sb);
+  seastar::future<OSDSuperblock> load_superblock();
+
+  using ec_profile_t = std::map<std::string, std::string>;
+  seastar::future<pg_pool_t,
+                  std::string,
+                  ec_profile_t> load_final_pool_info(int64_t pool);
+private:
+  static ghobject_t osdmap_oid(epoch_t epoch);
+  static ghobject_t final_pool_info_oid(int64_t pool);
+  static ghobject_t superblock_oid();
+};
diff --git a/src/crimson/osd/osdmap_service.h b/src/crimson/osd/osdmap_service.h
new file mode 100644
index 00000000..0a3aaed3
--- /dev/null
+++ b/src/crimson/osd/osdmap_service.h
@@ -0,0 +1,19 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+
+#pragma once
+
+#include <boost/smart_ptr/local_shared_ptr.hpp>
+
+#include "include/types.h"
+
+class OSDMap;
+
+class OSDMapService {
+public:
+  using cached_map_t = boost::local_shared_ptr<OSDMap>;
+  virtual ~OSDMapService() = default;
+  virtual seastar::future<cached_map_t> get_map(epoch_t e) = 0;
+  /// get the latest map
+  virtual cached_map_t get_map() const = 0;
+};
diff --git a/src/crimson/osd/pg.cc b/src/crimson/osd/pg.cc
new file mode 100644
index 00000000..bc7b8c2d
--- /dev/null
+++ b/src/crimson/osd/pg.cc
@@ -0,0 +1,6 @@
+#include "pg.h"
+
+PG::PG(pg_pool_t&& pool, std::string&& name, ec_profile_t&& ec_profile)
+{
+  // TODO
+}
diff --git a/src/crimson/osd/pg.h b/src/crimson/osd/pg.h
new file mode 100644
index 00000000..4bb672f4
--- /dev/null
+++ b/src/crimson/osd/pg.h
@@ -0,0 +1,21 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+
+#pragma once
+
+#include <boost/intrusive_ptr.hpp>
+#include <boost/smart_ptr/intrusive_ref_counter.hpp>
+#include <seastar/core/future.hh>
+
+#include "osd/osd_types.h"
+
+template<typename T> using Ref = boost::intrusive_ptr<T>;
+
+class PG : public boost::intrusive_ref_counter<
+  PG,
+  boost::thread_unsafe_counter>
+{
+  using ec_profile_t = std::map<std::string,std::string>;
+public:
+  PG(pg_pool_t&& pool, std::string&& name, ec_profile_t&& ec_profile);
+};
diff --git a/src/crimson/osd/pg_meta.cc b/src/crimson/osd/pg_meta.cc
new file mode 100644
index 00000000..2098e50a
--- /dev/null
+++ b/src/crimson/osd/pg_meta.cc
@@ -0,0 +1,104 @@
+#include "pg_meta.h"
+
+#include <string_view>
+
+#include "crimson/os/cyan_collection.h"
+#include "crimson/os/cyan_store.h"
+
+// prefix pgmeta_oid keys with _ so that PGLog::read_log_and_missing() can
+// easily skip them
+
+static const string_view infover_key = "_infover"sv;
+static const string_view info_key = "_info"sv;
+static const string_view biginfo_key = "_biginfo"sv;
+static const string_view epoch_key = "_epoch"sv;
+static const string_view fastinfo_key = "_fastinfo"sv;
+
+using ceph::os::CyanStore;
+
+PGMeta::PGMeta(CyanStore* store, spg_t pgid)
+  : store{store},
+    pgid{pgid}
+{}
+
+namespace {
+  template<typename T>
+  std::optional<T> find_value(const CyanStore::omap_values_t& values,
+                              string_view key)
+  {
+    auto found = values.find(key);
+    if (found == values.end()) {
+      return {};
+    }
+    auto p = found->second.cbegin();
+    T value;
+    decode(value, p);
+    return std::make_optional(std::move(value));
+  }
+}
+seastar::future<epoch_t> PGMeta::get_epoch()
+{
+  auto ch = store->open_collection(coll_t{pgid});
+  return store->omap_get_values(ch,
+                                pgid.make_pgmeta_oid(),
+                                {string{infover_key},
+                                 string{epoch_key}}).then(
+    [](auto&& values) {
+      {
+        // sanity check
+        auto infover = find_value<__u8>(values, infover_key);
+        assert(infover);
+        if (*infover < 10) {
+          throw std::runtime_error("incompatible pg meta");
+        }
+      }
+      {
+        auto epoch = find_value<epoch_t>(values, epoch_key);
+        assert(epoch);
+        return seastar::make_ready_future<epoch_t>(*epoch);
+      }
+    });
+}
+
+seastar::future<pg_info_t, PastIntervals> PGMeta::load()
+{
+  auto ch = store->open_collection(coll_t{pgid});
+  return store->omap_get_values(ch,
+                                pgid.make_pgmeta_oid(),
+                                {string{infover_key},
+                                 string{info_key},
+                                 string{biginfo_key},
+                                 string{fastinfo_key}}).then(
+    [this](auto&& values) {
+      {
+        // sanity check
+        auto infover = find_value<__u8>(values, infover_key);
+        assert(infover);
+        if (infover < 10) {
+          throw std::runtime_error("incompatible pg meta");
+        }
+      }
+      pg_info_t info;
+      {
+        auto found = find_value<pg_info_t>(values, info_key);
+        assert(found);
+        info = *std::move(found);
+      }
+      PastIntervals past_intervals;
+      {
+        using biginfo_t = std::pair<PastIntervals, decltype(info.purged_snaps)>;
+        auto big_info = find_value<biginfo_t>(values, biginfo_key);
+        assert(big_info);
+        past_intervals = std::move(big_info->first);
+        info.purged_snaps = std::move(big_info->second);
+      }
+      {
+        auto fast_info = find_value<pg_fast_info_t>(values, fastinfo_key);
+        assert(fast_info);
+        fast_info->try_apply_to(&info);
+      }
+      return seastar::make_ready_future<pg_info_t, PastIntervals>(
+        std::move(info),
+        std::move(past_intervals));
+    });
+}
diff --git a/src/crimson/osd/pg_meta.h b/src/crimson/osd/pg_meta.h
new file mode 100644
index 00000000..10f2234a
--- /dev/null
+++ b/src/crimson/osd/pg_meta.h
@@ -0,0 +1,22 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+
+#pragma once
+
+#include <seastar/core/future.hh>
+#include "osd/osd_types.h"
+
+namespace ceph::os {
+  class CyanStore;
+}
+
+/// PG related metadata
+class PGMeta
+{
+  ceph::os::CyanStore* store;
+  const spg_t pgid;
+public:
+  PGMeta(ceph::os::CyanStore *store, spg_t pgid);
+  seastar::future<epoch_t> get_epoch();
+  seastar::future<pg_info_t, PastIntervals> load();
+};
diff --git a/src/crimson/osd/state.h b/src/crimson/osd/state.h
new file mode 100644
index 00000000..4c445348
--- /dev/null
+++ b/src/crimson/osd/state.h
@@ -0,0 +1,71 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+
+#pragma once
+
+#include <string_view>
+#include <ostream>
+
+class OSDMap;
+
+class OSDState {
+
+  enum class State {
+    INITIALIZING,
+    PREBOOT,
+    BOOTING,
+    ACTIVE,
+    STOPPING,
+    WAITING_FOR_HEALTHY,
+  };
+
+  State state = State::INITIALIZING;
+
+public:
+  bool is_initializing() const {
+    return state == State::INITIALIZING;
+  }
+  bool is_preboot() const {
+    return state == State::PREBOOT;
+  }
+  bool is_booting() const {
+    return state == State::BOOTING;
+  }
+  bool is_active() const {
+    return state == State::ACTIVE;
+  }
+  bool is_stopping() const {
+    return state == State::STOPPING;
+  }
+  bool is_waiting_for_healthy() const {
+    return state == State::WAITING_FOR_HEALTHY;
+  }
+  void set_preboot() {
+    state = State::PREBOOT;
+  }
+  void set_booting() {
+    state = State::BOOTING;
+  }
+  void set_active() {
+    state = State::ACTIVE;
+  }
+  void set_stopping() {
+    state = State::STOPPING;
+  }
+  std::string_view to_string() const {
+    switch (state) {
+    case State::INITIALIZING: return "initializing";
+    case State::PREBOOT: return "preboot";
+    case State::BOOTING: return "booting";
+    case State::ACTIVE: return "active";
+    case State::STOPPING: return "stopping";
+    case State::WAITING_FOR_HEALTHY: return "waiting_for_healthy";
+    default: return "???";
+    }
+  }
+};
+
+inline std::ostream&
+operator<<(std::ostream& os, const OSDState& s) {
+  return os << s.to_string();
+}
diff --git a/src/crimson/thread/Condition.h b/src/crimson/thread/Condition.h
new file mode 100644
index 00000000..2a5c643d
--- /dev/null
+++ b/src/crimson/thread/Condition.h
@@ -0,0 +1,36 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+
+#pragma once
+
+#include <seastar/core/reactor.hh>
+#include <sys/eventfd.h>
+
+namespace ceph::thread {
+
+/// a synchronization primitive can be used to block a seastar thread, until
+/// another thread notifies it.
+class Condition {
+  seastar::file_desc file_desc;
+  int fd;
+  seastar::pollable_fd_state fd_state;
+  eventfd_t event = 0;
+public:
+  Condition()
+    : file_desc{seastar::file_desc::eventfd(0, 0)},
+      fd(file_desc.get()),
+      fd_state{std::move(file_desc)}
+  {}
+  seastar::future<> wait() {
+    return seastar::engine().read_some(fd_state, &event, sizeof(event))
+      .then([](size_t) {
+	  return seastar::now();
+	});
+  }
+  void notify() {
+    eventfd_t result = 1;
+    ::eventfd_write(fd, result);
+  }
+};
+
+} // namespace ceph::thread
diff --git a/src/crimson/thread/ThreadPool.cc b/src/crimson/thread/ThreadPool.cc
new file mode 100644
index 00000000..9df849b5
--- /dev/null
+++ b/src/crimson/thread/ThreadPool.cc
@@ -0,0 +1,76 @@
+#include "ThreadPool.h"
+
+#include <pthread.h>
+#include "crimson/net/Config.h"
+#include "include/intarith.h"
+
+#include "include/ceph_assert.h"
+
+namespace ceph::thread {
+
+ThreadPool::ThreadPool(size_t n_threads,
+                       size_t queue_sz,
+                       unsigned cpu_id)
+  : queue_size{round_up_to(queue_sz, seastar::smp::count)},
+    pending{queue_size}
+{
+  for (size_t i = 0; i < n_threads; i++) {
+    threads.emplace_back([this, cpu_id] {
+      pin(cpu_id);
+      loop();
+    });
+  }
+}
+
+ThreadPool::~ThreadPool()
+{
+  for (auto& thread : threads) {
+    thread.join();
+  }
+}
+
+void ThreadPool::pin(unsigned cpu_id)
+{
+  cpu_set_t cs;
+  CPU_ZERO(&cs);
+  CPU_SET(cpu_id, &cs);
+  [[maybe_unused]] auto r = pthread_setaffinity_np(pthread_self(),
+                                                   sizeof(cs), &cs);
+  ceph_assert(r == 0);
+}
+
+void ThreadPool::loop()
+{
+  for (;;) {
+    WorkItem* work_item = nullptr;
+    {
+      std::unique_lock lock{mutex};
+      cond.wait_for(lock,
+                    ceph::net::conf.threadpool_empty_queue_max_wait,
+                    [this, &work_item] {
+        return pending.pop(work_item) || is_stopping();
+      });
+    }
+    if (work_item) {
+      work_item->process();
+    } else if (is_stopping()) {
+      break;
+    }
+  }
+}
+
+seastar::future<> ThreadPool::start()
+{
+  auto slots_per_shard = queue_size / seastar::smp::count;
+  return submit_queue.start(slots_per_shard);
+}
+
+seastar::future<> ThreadPool::stop()
+{
+  return submit_queue.stop().then([this] {
+    stopping = true;
+    cond.notify_all();
+  });
+}
+
+} // namespace ceph::thread
diff --git a/src/crimson/thread/ThreadPool.h b/src/crimson/thread/ThreadPool.h
new file mode 100644
index 00000000..cfd72d2a
--- /dev/null
+++ b/src/crimson/thread/ThreadPool.h
@@ -0,0 +1,118 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*- 
+// vim: ts=8 sw=2 smarttab
+#pragma once
+
+#include <atomic>
+#include <condition_variable>
+#include <tuple>
+#include <type_traits>
+#include <boost/lockfree/queue.hpp>
+#include <boost/optional.hpp>
+#include <seastar/core/future.hh>
+#include <seastar/core/gate.hh>
+#include <seastar/core/semaphore.hh>
+#include <seastar/core/sharded.hh>
+
+#include "Condition.h"
+
+namespace ceph::thread {
+
+struct WorkItem {
+  virtual ~WorkItem() {}
+  virtual void process() = 0;
+};
+
+template<typename Func, typename T = std::invoke_result_t<Func>>
+struct Task final : WorkItem {
+  Func func;
+  seastar::future_state<T> state;
+  ceph::thread::Condition on_done;
+public:
+  explicit Task(Func&& f)
+    : func(std::move(f))
+  {}
+  void process() override {
+    try {
+      state.set(func());
+    } catch (...) {
+      state.set_exception(std::current_exception());
+    }
+    on_done.notify();
+  }
+  seastar::future<T> get_future() {
+    return on_done.wait().then([this] {
+      return seastar::make_ready_future<T>(state.get0(std::move(state).get()));
+    });
+  }
+};
+
+struct SubmitQueue {
+  seastar::semaphore free_slots;
+  seastar::gate pending_tasks;
+  explicit SubmitQueue(size_t num_free_slots)
+    : free_slots(num_free_slots)
+  {}
+  seastar::future<> stop() {
+    return pending_tasks.close();
+  }
+};
+
+/// an engine for scheduling non-seastar tasks from seastar fibers
+class ThreadPool {
+  std::atomic<bool> stopping = false;
+  std::mutex mutex;
+  std::condition_variable cond;
+  std::vector<std::thread> threads;
+  seastar::sharded<SubmitQueue> submit_queue;
+  const size_t queue_size;
+  boost::lockfree::queue<WorkItem*> pending;
+
+  void loop();
+  bool is_stopping() const {
+    return stopping.load(std::memory_order_relaxed);
+  }
+  static void pin(unsigned cpu_id);
+  seastar::semaphore& local_free_slots() {
+    return submit_queue.local().free_slots;
+  }
+  ThreadPool(const ThreadPool&) = delete;
+  ThreadPool& operator=(const ThreadPool&) = delete;
+public:
+  /**
+   * @param queue_sz the depth of pending queue. before a task is scheduled,
+   *                 it waits in this queue. we will round this number to
+   *                 multiple of the number of cores.
+   * @param n_threads the number of threads in this thread pool.
+   * @param cpu the CPU core to which this thread pool is assigned
+   * @note each @c Task has its own ceph::thread::Condition, which possesses
+   * possesses an fd, so we should keep the size of queue under a reasonable
+   * limit.
+   */
+  ThreadPool(size_t n_threads, size_t queue_sz, unsigned cpu);
+  ~ThreadPool();
+  seastar::future<> start();
+  seastar::future<> stop();
+  template<typename Func, typename...Args>
+  auto submit(Func&& func, Args&&... args) {
+    auto packaged = [func=std::move(func),
+                     args=std::forward_as_tuple(args...)] {
+      return std::apply(std::move(func), std::move(args));
+    };
+    return seastar::with_gate(submit_queue.local().pending_tasks,
+      [packaged=std::move(packaged), this] {
+        return local_free_slots().wait()
+          .then([packaged=std::move(packaged), this] {
+            auto task = new Task{std::move(packaged)};
+            auto fut = task->get_future();
+            pending.push(task);
+            cond.notify_one();
+            return fut.finally([task, this] {
+              local_free_slots().signal();
+              delete task;
+            });
+          });
+        });
+  }
+};
+
+} // namespace ceph::thread
diff --git a/src/crimson/thread/Throttle.cc b/src/crimson/thread/Throttle.cc
new file mode 100644
index 00000000..1d67e723
--- /dev/null
+++ b/src/crimson/thread/Throttle.cc
@@ -0,0 +1,59 @@
+#include "Throttle.h"
+
+namespace ceph::thread {
+
+int64_t Throttle::take(int64_t c)
+{
+  if (!max) {
+    return 0;
+  }
+  count += c;
+  return count;
+}
+
+int64_t Throttle::put(int64_t c)
+{
+  if (!max) {
+    return 0;
+  }
+  if (!c) {
+    return count;
+  }
+  on_free_slots.signal();
+  count -= c;
+  return count;
+}
+
+seastar::future<> Throttle::get(size_t c)
+{
+  if (!max) {
+    return seastar::now();
+  }
+  return on_free_slots.wait([this, c] {
+    return !_should_wait(c);
+  }).then([this, c] {
+    count += c;
+    return seastar::now();
+  });
+}
+
+void Throttle::reset_max(size_t m) {
+  if (max == m) {
+    return;
+  }
+
+  if (m > max) {
+    on_free_slots.signal();
+  }
+  max = m;
+}
+
+bool Throttle::_should_wait(size_t c) const {
+  if (!max) {
+    return false;
+  }
+  return ((c <= max && count + c > max) || // normally stay under max
+          (c >= max && count > max));      // except for large c
+}
+
+} // namespace ceph::thread::seastar
diff --git a/src/crimson/thread/Throttle.h b/src/crimson/thread/Throttle.h
new file mode 100644
index 00000000..c2342171
--- /dev/null
+++ b/src/crimson/thread/Throttle.h
@@ -0,0 +1,36 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:nil -*-
+// vim: ts=8 sw=2 smarttab
+
+#pragma once
+
+#include <seastar/core/condition-variable.hh>
+
+#include "common/ThrottleInterface.h"
+
+namespace ceph::thread {
+
+class Throttle final : public ThrottleInterface {
+  size_t max = 0;
+  size_t count = 0;
+  // we cannot change the "count" of seastar::semaphore after it is created,
+  // so use condition_variable instead.
+  seastar::condition_variable on_free_slots;
+public:
+  explicit Throttle(size_t m)
+    : max(m)
+  {}
+  int64_t take(int64_t c = 1) override;
+  int64_t put(int64_t c = 1) override;
+  seastar::future<> get(size_t c);
+  size_t get_current() const {
+    return count;
+  }
+  size_t get_max() const {
+    return max;
+  }
+  void reset_max(size_t m);
+private:
+  bool _should_wait(size_t c) const;
+};
+
+} // namespace ceph::thread