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diff --git a/src/ceph/src/mds/MDSContext.h b/src/ceph/src/mds/MDSContext.h
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+++ b/src/ceph/src/mds/MDSContext.h
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+// -*- 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) 2012 Red Hat
+ *
+ * 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.
+ * 
+ */
+
+
+#ifndef MDS_CONTEXT_H
+#define MDS_CONTEXT_H
+
+#include "include/Context.h"
+
+class MDSRank;
+
+
+/**
+ * Completion which has access to a reference to the global MDS instance.
+ *
+ * This class exists so that Context subclasses can provide the MDS pointer
+ * from a pointer they already had, e.g. MDCache or Locker, rather than
+ * necessarily having to carry around an extra MDS* pointer. 
+ */
+class MDSContext : public Context
+{
+protected:
+  virtual MDSRank *get_mds() = 0;
+};
+
+
+/**
+ * A context which must be called with the big MDS lock held.  Subclass
+ * this with a get_mds implementation.
+ */
+class MDSInternalContextBase : public MDSContext
+{
+public:
+    void complete(int r) override;
+};
+
+/**
+ * General purpose, lets you pass in an MDS pointer.
+ */
+class MDSInternalContext : public MDSInternalContextBase
+{
+protected:
+  MDSRank *mds;
+  MDSRank* get_mds() override;
+
+public:
+  explicit MDSInternalContext(MDSRank *mds_) : mds(mds_) {
+    assert(mds != NULL);
+  }
+};
+
+/**
+ * Wrap a regular Context up as an Internal context. Useful
+ * if you're trying to work with one of our more generic frameworks.
+ */
+class MDSInternalContextWrapper : public MDSInternalContextBase
+{
+protected:
+  MDSRank *mds;
+  Context *fin;
+  MDSRank *get_mds() override;
+public:
+  MDSInternalContextWrapper(MDSRank *m, Context *c) : mds(m), fin(c) {}
+  void finish(int r) override;
+};
+
+class MDSIOContextBase : public MDSContext
+{
+public:
+  void complete(int r) override;
+};
+
+/**
+ * Completion for an log operation, takes big MDSRank lock
+ * before executing finish function. Update log's safe pos
+ * after finish functuon return.
+ */
+class MDSLogContextBase : public MDSIOContextBase
+{
+protected:
+  uint64_t write_pos;
+public:
+  MDSLogContextBase() : write_pos(0) {}
+  void complete(int r) final;
+  void set_write_pos(uint64_t wp) { write_pos = wp; }
+  virtual void pre_finish(int r) {}
+};
+
+/**
+ * Completion for an I/O operation, takes big MDSRank lock
+ * before executing finish function.
+ */
+class MDSIOContext : public MDSIOContextBase
+{
+protected:
+  MDSRank *mds;
+  MDSRank* get_mds() override;
+
+public:
+  explicit MDSIOContext(MDSRank *mds_) : mds(mds_) {
+    assert(mds != NULL);
+  }
+};
+
+/**
+ * Wrap a regular Context up as an IO Context. Useful
+ * if you're trying to work with one of our more generic frameworks.
+ */
+class MDSIOContextWrapper : public MDSIOContextBase
+{
+protected:
+  MDSRank *mds;
+  Context *fin;
+  MDSRank *get_mds() override;
+public:
+  MDSIOContextWrapper(MDSRank *m, Context *c) : mds(m), fin(c) {}
+  void finish(int r) override;
+};
+
+/**
+ * No-op for callers expecting MDSInternalContextBase
+ */
+class C_MDSInternalNoop final : public MDSInternalContextBase
+{
+  MDSRank* get_mds() override {ceph_abort();}
+public:
+  void finish(int r) override {}
+  void complete(int r) override { delete this; }
+};
+
+
+/**
+ * This class is used where you have an MDSInternalContextBase but
+ * you sometimes want to call it back from an I/O completion.
+ */
+class C_IO_Wrapper : public MDSIOContext
+{
+protected:
+  bool async;
+  MDSInternalContextBase *wrapped;
+  void finish(int r) override {
+    wrapped->complete(r);
+    wrapped = nullptr;
+  }
+public:
+  C_IO_Wrapper(MDSRank *mds_, MDSInternalContextBase *wrapped_) :
+    MDSIOContext(mds_), async(true), wrapped(wrapped_) {
+    assert(wrapped != NULL);
+  }
+
+  ~C_IO_Wrapper() override {
+    if (wrapped != nullptr) {
+      delete wrapped;
+      wrapped = nullptr;
+    }
+  }
+  void complete(int r) final;
+};
+
+
+/**
+ * Gather needs a default-constructable class
+ */
+class MDSInternalContextGather : public MDSInternalContextBase
+{
+protected:
+  MDSRank *get_mds() override;
+};
+
+
+class MDSGather : public C_GatherBase<MDSInternalContextBase, MDSInternalContextGather>
+{
+public:
+  MDSGather(CephContext *cct, MDSInternalContextBase *onfinish) : C_GatherBase<MDSInternalContextBase, MDSInternalContextGather>(cct, onfinish) {}
+protected:
+  MDSRank *get_mds() override {return NULL;}
+};
+
+
+typedef C_GatherBuilderBase<MDSInternalContextBase, MDSGather> MDSGatherBuilder;
+
+#endif  // MDS_CONTEXT_H