Adding upstream version 14.2.21.upstream/14.2.21upstream

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

1 files changed, 1234 insertions, 0 deletions

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);
+};
+}