// -*- 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) 2004-2006 Sage Weil <sage@newdream.net>
 *
 * 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 "MDSRank.h"
#include "MDCache.h"
#include "Mutation.h"
#include "SessionMap.h"
#include "osdc/Filer.h"
#include "common/Finisher.h"

#include "common/config.h"
#include "common/errno.h"
#include "common/DecayCounter.h"
#include "include/ceph_assert.h"
#include "include/stringify.h"

#define dout_context g_ceph_context
#define dout_subsys ceph_subsys_mds
#undef dout_prefix
#define dout_prefix *_dout << "mds." << rank << ".sessionmap "

namespace {
class SessionMapIOContext : public MDSIOContextBase
{
  protected:
    SessionMap *sessionmap;
    MDSRank *get_mds() override {return sessionmap->mds;}
  public:
    explicit SessionMapIOContext(SessionMap *sessionmap_) : sessionmap(sessionmap_) {
      ceph_assert(sessionmap != NULL);
    }
};
};

void SessionMap::register_perfcounters()
{
  PerfCountersBuilder plb(g_ceph_context, "mds_sessions",
      l_mdssm_first, l_mdssm_last);

  plb.add_u64(l_mdssm_session_count, "session_count",
      "Session count", "sess", PerfCountersBuilder::PRIO_INTERESTING);

  plb.set_prio_default(PerfCountersBuilder::PRIO_USEFUL);
  plb.add_u64_counter(l_mdssm_session_add, "session_add",
      "Sessions added");
  plb.add_u64_counter(l_mdssm_session_remove, "session_remove",
      "Sessions removed");
  plb.add_u64(l_mdssm_session_open, "sessions_open",
              "Sessions currently open");
  plb.add_u64(l_mdssm_session_stale, "sessions_stale",
              "Sessions currently stale");
  plb.add_u64(l_mdssm_total_load, "total_load", "Total Load");
  plb.add_u64(l_mdssm_avg_load, "average_load", "Average Load");
  plb.add_u64(l_mdssm_avg_session_uptime, "avg_session_uptime",
               "Average session uptime");

  logger = plb.create_perf_counters();
  g_ceph_context->get_perfcounters_collection()->add(logger);
}

void SessionMap::dump()
{
  dout(10) << "dump" << dendl;
  for (ceph::unordered_map<entity_name_t,Session*>::iterator p = session_map.begin();
       p != session_map.end();
       ++p) 
    dout(10) << p->first << " " << p->second
	     << " state " << p->second->get_state_name()
	     << " completed " << p->second->info.completed_requests
	     << " free_prealloc_inos " << p->second->free_prealloc_inos
	     << " delegated_inos " << p->second->delegated_inos
	     << dendl;
}


// ----------------
// LOAD


object_t SessionMap::get_object_name() const
{
  char s[30];
  snprintf(s, sizeof(s), "mds%d_sessionmap", int(mds->get_nodeid()));
  return object_t(s);
}

namespace {
class C_IO_SM_Load : public SessionMapIOContext {
public:
  const bool first;  //< Am I the initial (header) load?
  int header_r;  //< Return value from OMAP header read
  int values_r;  //< Return value from OMAP value read
  bufferlist header_bl;
  std::map<std::string, bufferlist> session_vals;
  bool more_session_vals = false;

  C_IO_SM_Load(SessionMap *cm, const bool f)
    : SessionMapIOContext(cm), first(f), header_r(0), values_r(0) {}

  void finish(int r) override {
    sessionmap->_load_finish(r, header_r, values_r, first, header_bl, session_vals,
      more_session_vals);
  }
  void print(ostream& out) const override {
    out << "session_load";
  }
};
}


/**
 * Decode OMAP header.  Call this once when loading.
 */
void SessionMapStore::decode_header(
      bufferlist &header_bl)
{
  auto q = header_bl.cbegin();
  DECODE_START(1, q)
  decode(version, q);
  DECODE_FINISH(q);
}

void SessionMapStore::encode_header(
    bufferlist *header_bl)
{
  ENCODE_START(1, 1, *header_bl);
  encode(version, *header_bl);
  ENCODE_FINISH(*header_bl);
}

/**
 * Decode and insert some serialized OMAP values.  Call this
 * repeatedly to insert batched loads.
 */
void SessionMapStore::decode_values(std::map<std::string, bufferlist> &session_vals)
{
  for (std::map<std::string, bufferlist>::iterator i = session_vals.begin();
       i != session_vals.end(); ++i) {

    entity_inst_t inst;

    bool parsed = inst.name.parse(i->first);
    if (!parsed) {
      derr << "Corrupt entity name '" << i->first << "' in sessionmap" << dendl;
      throw buffer::malformed_input("Corrupt entity name in sessionmap");
    }

    Session *s = get_or_add_session(inst);
    if (s->is_closed()) {
      s->set_state(Session::STATE_OPEN);
      s->set_load_avg_decay_rate(decay_rate);
    }
    auto q = i->second.cbegin();
    s->decode(q);
  }
}

/**
 * An OMAP read finished.
 */
void SessionMap::_load_finish(
    int operation_r,
    int header_r,
    int values_r,
    bool first,
    bufferlist &header_bl,
    std::map<std::string, bufferlist> &session_vals,
    bool more_session_vals)
{
  if (operation_r < 0) {
    derr << "_load_finish got " << cpp_strerror(operation_r) << dendl;
    mds->clog->error() << "error reading sessionmap '" << get_object_name()
                       << "' " << operation_r << " ("
                       << cpp_strerror(operation_r) << ")";
    mds->damaged();
    ceph_abort();  // Should be unreachable because damaged() calls respawn()
  }

  // Decode header
  if (first) {
    if (header_r != 0) {
      derr << __func__ << ": header error: " << cpp_strerror(header_r) << dendl;
      mds->clog->error() << "error reading sessionmap header "
                         << header_r << " (" << cpp_strerror(header_r) << ")";
      mds->damaged();
      ceph_abort();  // Should be unreachable because damaged() calls respawn()
    }

    if(header_bl.length() == 0) {
      dout(4) << __func__ << ": header missing, loading legacy..." << dendl;
      load_legacy();
      return;
    }

    try {
      decode_header(header_bl);
    } catch (buffer::error &e) {
      mds->clog->error() << "corrupt sessionmap header: " << e.what();
      mds->damaged();
      ceph_abort();  // Should be unreachable because damaged() calls respawn()
    }
    dout(10) << __func__ << " loaded version " << version << dendl;
  }

  if (values_r != 0) {
    derr << __func__ << ": error reading values: "
      << cpp_strerror(values_r) << dendl;
    mds->clog->error() << "error reading sessionmap values: " 
                       << values_r << " (" << cpp_strerror(values_r) << ")";
    mds->damaged();
    ceph_abort();  // Should be unreachable because damaged() calls respawn()
  }

  // Decode session_vals
  try {
    decode_values(session_vals);
  } catch (buffer::error &e) {
    mds->clog->error() << "corrupt sessionmap values: " << e.what();
    mds->damaged();
    ceph_abort();  // Should be unreachable because damaged() calls respawn()
  }

  if (more_session_vals) {
    // Issue another read if we're not at the end of the omap
    const std::string last_key = session_vals.rbegin()->first;
    dout(10) << __func__ << ": continue omap load from '"
             << last_key << "'" << dendl;
    object_t oid = get_object_name();
    object_locator_t oloc(mds->get_metadata_pool());
    C_IO_SM_Load *c = new C_IO_SM_Load(this, false);
    ObjectOperation op;
    op.omap_get_vals(last_key, "", g_conf()->mds_sessionmap_keys_per_op,
		     &c->session_vals, &c->more_session_vals, &c->values_r);
    mds->objecter->read(oid, oloc, op, CEPH_NOSNAP, NULL, 0,
        new C_OnFinisher(c, mds->finisher));
  } else {
    // I/O is complete.  Update `by_state`
    dout(10) << __func__ << ": omap load complete" << dendl;
    for (ceph::unordered_map<entity_name_t, Session*>::iterator i = session_map.begin();
         i != session_map.end(); ++i) {
      Session *s = i->second;
      auto by_state_entry = by_state.find(s->get_state());
      if (by_state_entry == by_state.end())
	by_state_entry = by_state.emplace(s->get_state(),
					  new xlist<Session*>).first;
      by_state_entry->second->push_back(&s->item_session_list);
    }

    // Population is complete.  Trigger load waiters.
    dout(10) << __func__ << ": v " << version 
	   << ", " << session_map.size() << " sessions" << dendl;
    projected = committing = committed = version;
    dump();
    finish_contexts(g_ceph_context, waiting_for_load);
  }
}

/**
 * Populate session state from OMAP records in this
 * rank's sessionmap object.
 */
void SessionMap::load(MDSContext *onload)
{
  dout(10) << "load" << dendl;

  if (onload)
    waiting_for_load.push_back(onload);
  
  C_IO_SM_Load *c = new C_IO_SM_Load(this, true);
  object_t oid = get_object_name();
  object_locator_t oloc(mds->get_metadata_pool());

  ObjectOperation op;
  op.omap_get_header(&c->header_bl, &c->header_r);
  op.omap_get_vals("", "", g_conf()->mds_sessionmap_keys_per_op,
		   &c->session_vals, &c->more_session_vals, &c->values_r);

  mds->objecter->read(oid, oloc, op, CEPH_NOSNAP, NULL, 0, new C_OnFinisher(c, mds->finisher));
}

namespace {
class C_IO_SM_LoadLegacy : public SessionMapIOContext {
public:
  bufferlist bl;
  explicit C_IO_SM_LoadLegacy(SessionMap *cm) : SessionMapIOContext(cm) {}
  void finish(int r) override {
    sessionmap->_load_legacy_finish(r, bl);
  }
  void print(ostream& out) const override {
    out << "session_load_legacy";
  }
};
}


/**
 * Load legacy (object data blob) SessionMap format, assuming
 * that waiting_for_load has already been populated with
 * the relevant completion.  This is the fallback if we do not
 * find an OMAP header when attempting to load normally.
 */
void SessionMap::load_legacy()
{
  dout(10) << __func__ << dendl;

  C_IO_SM_LoadLegacy *c = new C_IO_SM_LoadLegacy(this);
  object_t oid = get_object_name();
  object_locator_t oloc(mds->get_metadata_pool());

  mds->objecter->read_full(oid, oloc, CEPH_NOSNAP, &c->bl, 0,
			   new C_OnFinisher(c, mds->finisher));
}

void SessionMap::_load_legacy_finish(int r, bufferlist &bl)
{ 
  auto blp = bl.cbegin();
  if (r < 0) {
    derr << "_load_finish got " << cpp_strerror(r) << dendl;
    ceph_abort_msg("failed to load sessionmap");
  }
  dump();
  decode_legacy(blp);  // note: this sets last_cap_renew = now()
  dout(10) << "_load_finish v " << version 
	   << ", " << session_map.size() << " sessions, "
	   << bl.length() << " bytes"
	   << dendl;
  projected = committing = committed = version;
  dump();

  // Mark all sessions dirty, so that on next save() we will write
  // a complete OMAP version of the data loaded from the legacy format
  for (ceph::unordered_map<entity_name_t, Session*>::iterator i = session_map.begin();
       i != session_map.end(); ++i) {
    // Don't use mark_dirty because on this occasion we want to ignore the
    // keys_per_op limit and do one big write (upgrade must be atomic)
    dirty_sessions.insert(i->first);
  }
  loaded_legacy = true;

  finish_contexts(g_ceph_context, waiting_for_load);
}


// ----------------
// SAVE

namespace {
class C_IO_SM_Save : public SessionMapIOContext {
  version_t version;
public:
  C_IO_SM_Save(SessionMap *cm, version_t v) : SessionMapIOContext(cm), version(v) {}
  void finish(int r) override {
    if (r != 0) {
      get_mds()->handle_write_error(r);
    } else {
      sessionmap->_save_finish(version);
    }
  }
  void print(ostream& out) const override {
    out << "session_save";
  }
};
}

void SessionMap::save(MDSContext *onsave, version_t needv)
{
  dout(10) << __func__ << ": needv " << needv << ", v " << version << dendl;
 
  if (needv && committing >= needv) {
    ceph_assert(committing > committed);
    commit_waiters[committing].push_back(onsave);
    return;
  }

  commit_waiters[version].push_back(onsave);

  committing = version;
  SnapContext snapc;
  object_t oid = get_object_name();
  object_locator_t oloc(mds->get_metadata_pool());

  ObjectOperation op;

  /* Compose OSD OMAP transaction for full write */
  bufferlist header_bl;
  encode_header(&header_bl);
  op.omap_set_header(header_bl);

  /* If we loaded a legacy sessionmap, then erase the old data.  If
   * an old-versioned MDS tries to read it, it'll fail out safely
   * with an end_of_buffer exception */
  if (loaded_legacy) {
    dout(4) << __func__ << " erasing legacy sessionmap" << dendl;
    op.truncate(0);
    loaded_legacy = false;  // only need to truncate once.
  }

  dout(20) << " updating keys:" << dendl;
  map<string, bufferlist> to_set;
  for(std::set<entity_name_t>::iterator i = dirty_sessions.begin();
      i != dirty_sessions.end(); ++i) {
    const entity_name_t name = *i;
    Session *session = session_map[name];

    if (session->is_open() ||
	session->is_closing() ||
	session->is_stale() ||
	session->is_killing()) {
      dout(20) << "  " << name << dendl;
      // Serialize K
      CachedStackStringStream css;
      *css << name;

      // Serialize V
      bufferlist bl;
      session->info.encode(bl, mds->mdsmap->get_up_features());

      // Add to RADOS op
      to_set[std::string(css->strv())] = bl;

      session->clear_dirty_completed_requests();
    } else {
      dout(20) << "  " << name << " (ignoring)" << dendl;
    }
  }
  if (!to_set.empty()) {
    op.omap_set(to_set);
  }

  dout(20) << " removing keys:" << dendl;
  set<string> to_remove;
  for(std::set<entity_name_t>::const_iterator i = null_sessions.begin();
      i != null_sessions.end(); ++i) {
    dout(20) << "  " << *i << dendl;
    CachedStackStringStream css;
    *css << *i;
    to_remove.insert(css->str());
  }
  if (!to_remove.empty()) {
    op.omap_rm_keys(to_remove);
  }

  dirty_sessions.clear();
  null_sessions.clear();

  mds->objecter->mutate(oid, oloc, op, snapc,
			ceph::real_clock::now(),
			0,
			new C_OnFinisher(new C_IO_SM_Save(this, version),
					 mds->finisher));
}

void SessionMap::_save_finish(version_t v)
{
  dout(10) << "_save_finish v" << v << dendl;
  committed = v;

  finish_contexts(g_ceph_context, commit_waiters[v]);
  commit_waiters.erase(v);
}


/**
 * Deserialize sessions, and update by_state index
 */
void SessionMap::decode_legacy(bufferlist::const_iterator &p)
{
  // Populate `sessions`
  SessionMapStore::decode_legacy(p);

  // Update `by_state`
  for (ceph::unordered_map<entity_name_t, Session*>::iterator i = session_map.begin();
       i != session_map.end(); ++i) {
    Session *s = i->second;
    auto by_state_entry = by_state.find(s->get_state());
    if (by_state_entry == by_state.end())
      by_state_entry = by_state.emplace(s->get_state(),
					new xlist<Session*>).first;
    by_state_entry->second->push_back(&s->item_session_list);
  }
}

uint64_t SessionMap::set_state(Session *session, int s) {
  if (session->state != s) {
    session->set_state(s);
    auto by_state_entry = by_state.find(s);
    if (by_state_entry == by_state.end())
      by_state_entry = by_state.emplace(s, new xlist<Session*>).first;
    by_state_entry->second->push_back(&session->item_session_list);

    if (session->is_open() || session->is_stale()) {
      session->set_load_avg_decay_rate(decay_rate);
    }

    // refresh number of sessions for states which have perf
    // couters associated
    logger->set(l_mdssm_session_open,
                get_session_count_in_state(Session::STATE_OPEN));
    logger->set(l_mdssm_session_stale,
                get_session_count_in_state(Session::STATE_STALE));
  }

  return session->get_state_seq();
}

void SessionMapStore::decode_legacy(bufferlist::const_iterator& p)
{
  auto now = clock::now();
  uint64_t pre;
  decode(pre, p);
  if (pre == (uint64_t)-1) {
    DECODE_START_LEGACY_COMPAT_LEN(3, 3, 3, p);
    ceph_assert(struct_v >= 2);
    
    decode(version, p);
    
    while (!p.end()) {
      entity_inst_t inst;
      decode(inst.name, p);
      Session *s = get_or_add_session(inst);
      if (s->is_closed()) {
        s->set_state(Session::STATE_OPEN);
        s->set_load_avg_decay_rate(decay_rate);
      }
      s->decode(p);
    }

    DECODE_FINISH(p);
  } else {
    // --- old format ----
    version = pre;

    // this is a meaningless upper bound.  can be ignored.
    __u32 n;
    decode(n, p);
    
    while (n-- && !p.end()) {
      auto p2 = p;
      Session *s = new Session(ConnectionRef());
      s->info.decode(p);
      {
        auto& name = s->info.inst.name;
        auto it = session_map.find(name);
        if (it != session_map.end()) {
	  // eager client connected too fast!  aie.
	  dout(10) << " already had session for " << name << ", recovering" << dendl;
	  delete s;
	  s = it->second;
	  p = p2;
	  s->info.decode(p);
        } else {
	  it->second = s;
        }
      }
      s->set_state(Session::STATE_OPEN);
      s->set_load_avg_decay_rate(decay_rate);
      s->last_cap_renew = now;
    }
  }
}

void Session::dump(Formatter *f, bool cap_dump) const
{
  f->dump_int("id", info.inst.name.num());
  f->dump_object("entity", info.inst);
  f->dump_string("state", get_state_name());
  f->dump_int("num_leases", leases.size());
  f->dump_int("num_caps", caps.size());
  if (cap_dump) {
    f->open_array_section("caps");
    for (const auto& cap : caps) {
      f->dump_object("cap", *cap);
    }
    f->close_section();
  }
  if (is_open() || is_stale()) {
    f->dump_unsigned("request_load_avg", get_load_avg());
  }
  f->dump_float("uptime", get_session_uptime());
  f->dump_unsigned("requests_in_flight", get_request_count());
  f->dump_unsigned("num_completed_requests", get_num_completed_requests());
  f->dump_unsigned("num_completed_flushes", get_num_completed_flushes());
  f->dump_bool("reconnecting", reconnecting);
  f->dump_object("recall_caps", recall_caps);
  f->dump_object("release_caps", release_caps);
  f->dump_object("recall_caps_throttle", recall_caps_throttle);
  f->dump_object("recall_caps_throttle2o", recall_caps_throttle2o);
  f->dump_object("session_cache_liveness", session_cache_liveness);
  f->dump_object("cap_acquisition", cap_acquisition);

  f->open_array_section("delegated_inos");
  for (const auto& [start, len] : delegated_inos) {
    f->open_object_section("ino_range");
    f->dump_stream("start") << start;
    f->dump_unsigned("length", len);
    f->close_section();
  }
  f->close_section();

  info.dump(f);
}

void SessionMapStore::dump(Formatter *f) const
{
  f->open_array_section("sessions");
  for (const auto& p : session_map) {
    f->dump_object("session", *p.second);
  }
  f->close_section(); // Sessions
}

void SessionMapStore::generate_test_instances(std::list<SessionMapStore*>& ls)
{
  // pretty boring for now
  ls.push_back(new SessionMapStore());
}

void SessionMap::wipe()
{
  dout(1) << "wipe start" << dendl;
  dump();
  while (!session_map.empty()) {
    Session *s = session_map.begin()->second;
    remove_session(s);
  }
  version = ++projected;
  dout(1) << "wipe result" << dendl;
  dump();
  dout(1) << "wipe done" << dendl;
}

void SessionMap::wipe_ino_prealloc()
{
  for (ceph::unordered_map<entity_name_t,Session*>::iterator p = session_map.begin(); 
       p != session_map.end(); 
       ++p) {
    p->second->pending_prealloc_inos.clear();
    p->second->free_prealloc_inos.clear();
    p->second->delegated_inos.clear();
    p->second->info.prealloc_inos.clear();
  }
  projected = ++version;
}

void SessionMap::add_session(Session *s)
{
  dout(10) << __func__ << " s=" << s << " name=" << s->info.inst.name << dendl;

  ceph_assert(session_map.count(s->info.inst.name) == 0);
  session_map[s->info.inst.name] = s;
  auto by_state_entry = by_state.find(s->state);
  if (by_state_entry == by_state.end())
    by_state_entry = by_state.emplace(s->state, new xlist<Session*>).first;
  by_state_entry->second->push_back(&s->item_session_list);
  s->get();

  update_average_birth_time(*s);

  logger->set(l_mdssm_session_count, session_map.size());
  logger->inc(l_mdssm_session_add);
}

void SessionMap::remove_session(Session *s)
{
  dout(10) << __func__ << " s=" << s << " name=" << s->info.inst.name << dendl;

  update_average_birth_time(*s, false);

  s->trim_completed_requests(0);
  s->item_session_list.remove_myself();
  session_map.erase(s->info.inst.name);
  dirty_sessions.erase(s->info.inst.name);
  null_sessions.insert(s->info.inst.name);
  s->put();

  logger->set(l_mdssm_session_count, session_map.size());
  logger->inc(l_mdssm_session_remove);
}

void SessionMap::touch_session(Session *session)
{
  dout(10) << __func__ << " s=" << session << " name=" << session->info.inst.name << dendl;

  // Move to the back of the session list for this state (should
  // already be on a list courtesy of add_session and set_state)
  ceph_assert(session->item_session_list.is_on_list());
  auto by_state_entry = by_state.find(session->state);
  if (by_state_entry == by_state.end())
    by_state_entry = by_state.emplace(session->state,
				      new xlist<Session*>).first;
  by_state_entry->second->push_back(&session->item_session_list);

  session->last_cap_renew = clock::now();
}

void SessionMap::_mark_dirty(Session *s, bool may_save)
{
  if (dirty_sessions.count(s->info.inst.name))
    return;

  if (may_save &&
      dirty_sessions.size() >= g_conf()->mds_sessionmap_keys_per_op) {
    // Pre-empt the usual save() call from journal segment trim, in
    // order to avoid building up an oversized OMAP update operation
    // from too many sessions modified at once
    save(new C_MDSInternalNoop, version);
  }

  null_sessions.erase(s->info.inst.name);
  dirty_sessions.insert(s->info.inst.name);
}

void SessionMap::mark_dirty(Session *s, bool may_save)
{
  dout(20) << __func__ << " s=" << s << " name=" << s->info.inst.name
    << " v=" << version << dendl;

  _mark_dirty(s, may_save);
  version++;
  s->pop_pv(version);
}

void SessionMap::replay_dirty_session(Session *s)
{
  dout(20) << __func__ << " s=" << s << " name=" << s->info.inst.name
    << " v=" << version << dendl;

  _mark_dirty(s, false);

  replay_advance_version();
}

void SessionMap::replay_advance_version()
{
  version++;
  projected = version;
}

void SessionMap::replay_open_sessions(version_t event_cmapv,
			    map<client_t,entity_inst_t>& client_map,
			    map<client_t,client_metadata_t>& client_metadata_map)
{
  unsigned already_saved;

  if (version + client_map.size() < event_cmapv)
    goto bad;

  // Server::finish_force_open_sessions() marks sessions dirty one by one.
  // Marking a session dirty may flush all existing dirty sessions. So it's
  // possible that some sessions are already saved in sessionmap.
  already_saved = client_map.size() - (event_cmapv - version);
  for (const auto& p : client_map) {
    Session *s = get_or_add_session(p.second);
    auto q = client_metadata_map.find(p.first);
    if (q != client_metadata_map.end())
      s->info.client_metadata.merge(q->second);

    if (already_saved > 0) {
      if (s->is_closed())
	goto bad;

      --already_saved;
      continue;
    }

    set_state(s, Session::STATE_OPEN);
    replay_dirty_session(s);
  }
  return;

bad:
  mds->clog->error() << "error replaying open sessions(" << client_map.size()
		     << ") sessionmap v " << event_cmapv << " table " << version;
  ceph_assert(g_conf()->mds_wipe_sessions);
  mds->sessionmap.wipe();
  mds->sessionmap.set_version(event_cmapv);
}

version_t SessionMap::mark_projected(Session *s)
{
  dout(20) << __func__ << " s=" << s << " name=" << s->info.inst.name
    << " pv=" << projected << " -> " << projected + 1 << dendl;
  ++projected;
  s->push_pv(projected);
  return projected;
}

namespace {
class C_IO_SM_Save_One : public SessionMapIOContext {
  MDSContext *on_safe;
public:
  C_IO_SM_Save_One(SessionMap *cm, MDSContext *on_safe_)
    : SessionMapIOContext(cm), on_safe(on_safe_) {}
  void finish(int r) override {
    if (r != 0) {
      get_mds()->handle_write_error(r);
    } else {
      on_safe->complete(r);
    }
  }
  void print(ostream& out) const override {
    out << "session_save_one";
  }
};
}


void SessionMap::save_if_dirty(const std::set<entity_name_t> &tgt_sessions,
                               MDSGatherBuilder *gather_bld)
{
  ceph_assert(gather_bld != NULL);

  std::vector<entity_name_t> write_sessions;

  // Decide which sessions require a write
  for (std::set<entity_name_t>::iterator i = tgt_sessions.begin();
       i != tgt_sessions.end(); ++i) {
    const entity_name_t &session_id = *i;

    if (session_map.count(session_id) == 0) {
      // Session isn't around any more, never mind.
      continue;
    }

    Session *session = session_map[session_id];
    if (!session->has_dirty_completed_requests()) {
      // Session hasn't had completed_requests
      // modified since last write, no need to
      // write it now.
      continue;
    }

    if (dirty_sessions.count(session_id) > 0) {
      // Session is already dirtied, will be written, no
      // need to pre-empt that.
      continue;
    }
    // Okay, passed all our checks, now we write
    // this session out.  The version we write
    // into the OMAP may now be higher-versioned
    // than the version in the header, but that's
    // okay because it's never a problem to have
    // an overly-fresh copy of a session.
    write_sessions.push_back(*i);
  }

  dout(4) << __func__ << ": writing " << write_sessions.size() << dendl;

  // Batch writes into mds_sessionmap_keys_per_op
  const uint32_t kpo = g_conf()->mds_sessionmap_keys_per_op;
  map<string, bufferlist> to_set;
  for (uint32_t i = 0; i < write_sessions.size(); ++i) {
    const entity_name_t &session_id = write_sessions[i];
    Session *session = session_map[session_id];
    session->clear_dirty_completed_requests();

    // Serialize K
    CachedStackStringStream css;
    *css << session_id;

    // Serialize V
    bufferlist bl;
    session->info.encode(bl, mds->mdsmap->get_up_features());

    // Add to RADOS op
    to_set[css->str()] = bl;

    // Complete this write transaction?
    if (i == write_sessions.size() - 1
        || i % kpo == kpo - 1) {
      ObjectOperation op;
      op.omap_set(to_set);
      to_set.clear(); // clear to start a new transaction      

      SnapContext snapc;
      object_t oid = get_object_name();
      object_locator_t oloc(mds->get_metadata_pool());
      MDSContext *on_safe = gather_bld->new_sub();
      mds->objecter->mutate(oid, oloc, op, snapc,
			    ceph::real_clock::now(), 0,
			    new C_OnFinisher(
			      new C_IO_SM_Save_One(this, on_safe),
			      mds->finisher));
    }
  }
}

// =================
// Session

#undef dout_prefix
#define dout_prefix *_dout << "Session "

/**
 * Calculate the length of the `requests` member list,
 * because elist does not have a size() method.
 *
 * O(N) runtime.
 */
size_t Session::get_request_count() const
{
  size_t result = 0;
  for (auto p = requests.begin(); !p.end(); ++p)
    ++result;
  return result;
}

/**
 * Capped in response to a CEPH_MSG_CLIENT_CAPRELEASE message,
 * with n_caps equal to the number of caps that were released
 * in the message.  Used to update state about how many caps a
 * client has released since it was last instructed to RECALL_STATE.
 */
void Session::notify_cap_release(size_t n_caps)
{
  recall_caps.hit(-(double)n_caps);
  release_caps.hit(n_caps);
}

/**
 * Called when a CEPH_MSG_CLIENT_SESSION->CEPH_SESSION_RECALL_STATE
 * message is sent to the client.  Update our recall-related state
 * in order to generate health metrics if the session doesn't see
 * a commensurate number of calls to ::notify_cap_release
 */
uint64_t Session::notify_recall_sent(size_t new_limit)
{
  const auto num_caps = caps.size();
  ceph_assert(new_limit < num_caps);  // Behaviour of Server::recall_client_state
  const auto count = num_caps-new_limit;
  uint64_t new_change;
  if (recall_limit != new_limit) {
    new_change = count;
  } else {
    new_change = 0; /* no change! */
  }

  /* Always hit the session counter as a RECALL message is still sent to the
   * client and we do not want the MDS to burn its global counter tokens on a
   * session that is not releasing caps (i.e. allow the session counter to
   * throttle future RECALL messages).
   */
  recall_caps_throttle.hit(count);
  recall_caps_throttle2o.hit(count);
  recall_caps.hit(count);
  return new_change;
}

/**
 * Use client metadata to generate a somewhat-friendlier
 * name for the client than its session ID.
 *
 * This is *not* guaranteed to be unique, and any machine
 * consumers of session-related output should always use
 * the session ID as a primary capacity and use this only
 * as a presentation hint.
 */
void Session::_update_human_name()
{
  auto info_client_metadata_entry = info.client_metadata.find("hostname");
  if (info_client_metadata_entry != info.client_metadata.end()) {
    // Happy path, refer to clients by hostname
    human_name = info_client_metadata_entry->second;
    if (!info.auth_name.has_default_id()) {
      // When a non-default entity ID is set by the user, assume they
      // would like to see it in references to the client, if it's
      // reasonable short.  Limit the length because we don't want
      // to put e.g. uuid-generated names into a "human readable"
      // rendering.
      const int arbitrarily_short = 16;
      if (info.auth_name.get_id().size() < arbitrarily_short) {
        human_name += std::string(":") + info.auth_name.get_id();
      }
    }
  } else {
    // Fallback, refer to clients by ID e.g. client.4567
    human_name = stringify(info.inst.name.num());
  }
}

void Session::decode(bufferlist::const_iterator &p)
{
  info.decode(p);

  free_prealloc_inos = info.prealloc_inos;

  _update_human_name();
}

int Session::check_access(CInode *in, unsigned mask,
			  int caller_uid, int caller_gid,
			  const vector<uint64_t> *caller_gid_list,
			  int new_uid, int new_gid)
{
  string path;
  CInode *diri = NULL;
  if (!in->is_base())
    diri = in->get_projected_parent_dn()->get_dir()->get_inode();
  if (diri && diri->is_stray()){
    path = in->get_projected_inode()->stray_prior_path;
    dout(20) << __func__ << " stray_prior_path " << path << dendl;
  } else {
    in->make_path_string(path, true);
    dout(20) << __func__ << " path " << path << dendl;
  }
  if (path.length())
    path = path.substr(1);    // drop leading /

  const auto& inode = in->get_inode();
  if (in->is_dir() &&
      inode->has_layout() &&
      inode->layout.pool_ns.length() &&
      !connection->has_feature(CEPH_FEATURE_FS_FILE_LAYOUT_V2)) {
    dout(10) << __func__ << " client doesn't support FS_FILE_LAYOUT_V2" << dendl;
    return -CEPHFS_EIO;
  }

  if (!auth_caps.is_capable(path, inode->uid, inode->gid, inode->mode,
			    caller_uid, caller_gid, caller_gid_list, mask,
			    new_uid, new_gid,
			    info.inst.addr)) {
    return -CEPHFS_EACCES;
  }
  return 0;
}

// track total and per session load
void SessionMap::hit_session(Session *session) {
  uint64_t sessions = get_session_count_in_state(Session::STATE_OPEN) +
                      get_session_count_in_state(Session::STATE_STALE) +
                      get_session_count_in_state(Session::STATE_CLOSING);
  ceph_assert(sessions != 0);

  double total_load = total_load_avg.hit();
  double avg_load = total_load / sessions;

  logger->set(l_mdssm_total_load, (uint64_t)total_load);
  logger->set(l_mdssm_avg_load, (uint64_t)avg_load);

  session->hit_session();
}

void SessionMap::handle_conf_change(const std::set<std::string>& changed)
{
  auto apply_to_open_sessions = [this](auto f) {
    if (auto it = by_state.find(Session::STATE_OPEN); it != by_state.end()) {
      for (const auto &session : *(it->second)) {
        f(session);
      }
    }
    if (auto it = by_state.find(Session::STATE_STALE); it != by_state.end()) {
      for (const auto &session : *(it->second)) {
        f(session);
      }
    }
  };

  if (changed.count("mds_request_load_average_decay_rate")) {
    auto d = g_conf().get_val<double>("mds_request_load_average_decay_rate");

    decay_rate = d;
    total_load_avg = DecayCounter(d);

    auto mut = [d](auto s) {
      s->set_load_avg_decay_rate(d);
    };
    apply_to_open_sessions(mut);
  }
  if (changed.count("mds_recall_max_decay_rate")) {
    auto d = g_conf().get_val<double>("mds_recall_max_decay_rate");
    auto mut = [d](auto s) {
      s->recall_caps_throttle = DecayCounter(d);
    };
    apply_to_open_sessions(mut);
  }
  if (changed.count("mds_recall_warning_decay_rate")) {
    auto d = g_conf().get_val<double>("mds_recall_warning_decay_rate");
    auto mut = [d](auto s) {
      s->recall_caps = DecayCounter(d);
      s->release_caps = DecayCounter(d);
    };
    apply_to_open_sessions(mut);
  }
  if (changed.count("mds_session_cache_liveness_decay_rate")) {
    auto d = g_conf().get_val<double>("mds_session_cache_liveness_decay_rate");
    auto mut = [d](auto s) {
      s->session_cache_liveness = DecayCounter(d);
      s->session_cache_liveness.hit(s->caps.size()); /* so the MDS doesn't immediately start trimming a new session */
    };
    apply_to_open_sessions(mut);
  }
  if (changed.count("mds_session_cap_acquisition_decay_rate")) {
    auto d = g_conf().get_val<double>("mds_session_cap_acquisition_decay_rate");
    auto mut = [d](auto s) {
      s->cap_acquisition = DecayCounter(d);
    };
    apply_to_open_sessions(mut);
  }
}

void SessionMap::update_average_session_age() {
  if (!session_map.size()) {
    return;
  }

  double avg_uptime = std::chrono::duration<double>(clock::now()-avg_birth_time).count();
  logger->set(l_mdssm_avg_session_uptime, (uint64_t)avg_uptime);
}

int SessionFilter::parse(
    const std::vector<std::string> &args,
    std::ostream *ss)
{
  ceph_assert(ss != NULL);

  for (const auto &s : args) {
    dout(20) << __func__ << " parsing filter '" << s << "'" << dendl;

    auto eq = s.find("=");
    if (eq == std::string::npos || eq == s.size()) {
      // allow this to be a bare id for compatibility with pre-octopus asok
      // 'session evict'.
      std::string err;
      id = strict_strtoll(s.c_str(), 10, &err);
      if (!err.empty()) {
	*ss << "Invalid filter '" << s << "'";
	return -CEPHFS_EINVAL;
      }
      return 0;
    }

    // Keys that start with this are to be taken as referring
    // to freeform client metadata fields.
    const std::string metadata_prefix("client_metadata.");

    auto k = s.substr(0, eq);
    auto v = s.substr(eq + 1);

    dout(20) << __func__ << " parsed k='" << k << "', v='" << v << "'" << dendl;

    if (k.compare(0, metadata_prefix.size(), metadata_prefix) == 0
        && k.size() > metadata_prefix.size()) {
      // Filter on arbitrary metadata key (no fixed schema for this,
      // so anything after the dot is a valid field to filter on)
      auto metadata_key = k.substr(metadata_prefix.size());
      metadata.insert(std::make_pair(metadata_key, v));
    } else if (k == "auth_name") {
      // Filter on client entity name
      auth_name = v;
    } else if (k == "state") {
      state = v;
    } else if (k == "id") {
      std::string err;
      id = strict_strtoll(v.c_str(), 10, &err);
      if (!err.empty()) {
        *ss << err;
        return -CEPHFS_EINVAL;
      }
    } else if (k == "reconnecting") {

      /**
       * Strict boolean parser.  Allow true/false/0/1.
       * Anything else is -CEPHFS_EINVAL.
       */
      auto is_true = [](std::string_view bstr, bool *out) -> bool
      {
        ceph_assert(out != nullptr);

        if (bstr == "true" || bstr == "1") {
          *out = true;
          return 0;
        } else if (bstr == "false" || bstr == "0") {
          *out = false;
          return 0;
        } else {
          return -CEPHFS_EINVAL;
        }
      };

      bool bval;
      int r = is_true(v, &bval);
      if (r == 0) {
        set_reconnecting(bval);
      } else {
        *ss << "Invalid boolean value '" << v << "'";
        return -CEPHFS_EINVAL;
      }
    } else {
      *ss << "Invalid filter key '" << k << "'";
      return -CEPHFS_EINVAL;
    }
  }

  return 0;
}

bool SessionFilter::match(
    const Session &session,
    std::function<bool(client_t)> is_reconnecting) const
{
  for (const auto &m : metadata) {
    const auto &k = m.first;
    const auto &v = m.second;
    auto it = session.info.client_metadata.find(k);
    if (it == session.info.client_metadata.end()) {
      return false;
    }
    if (it->second != v) {
      return false;
    }
  }

  if (!auth_name.empty() && auth_name != session.info.auth_name.get_id()) {
    return false;
  }

  if (!state.empty() && state != session.get_state_name()) {
    return false;
  }

  if (id != 0 && id != session.info.inst.name.num()) {
    return false;
  }

  if (reconnecting.first) {
    const bool am_reconnecting = is_reconnecting(session.info.inst.name.num());
    if (reconnecting.second != am_reconnecting) {
      return false;
    }
  }

  return true;
}

std::ostream& operator<<(std::ostream &out, const Session &s)
{
 if (s.get_human_name() == stringify(s.get_client())) {
   out << s.get_human_name();
 } else {
   out << s.get_human_name() << " (" << std::dec << s.get_client() << ")";
 }
 return out;
}