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diff --git a/src/ceph/src/client/barrier.cc b/src/ceph/src/client/barrier.cc
new file mode 100644
index 0000000..b8a9751
--- /dev/null
+++ b/src/ceph/src/client/barrier.cc
@@ -0,0 +1,196 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+/*
+ *
+ * Copyright (C) 2012 CohortFS, LLC.
+ *
+ * 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.
+ *
+ */
+
+#if defined(__FreeBSD__)
+#include <sys/param.h>
+#endif
+
+#include "include/Context.h"
+#include "Client.h"
+#include "barrier.h"
+#include "include/assert.h"
+
+#undef dout_prefix
+#define dout_prefix *_dout << "client." << whoami << " "
+
+#define dout_subsys ceph_subsys_client
+
+#define cldout(cl, v)  dout_impl((cl)->cct, dout_subsys, v) \
+  *_dout << "client." << cl->whoami << " "
+
+/* C_Block_Sync */
+class C_Block_Sync : public Context {
+private:
+  Client *cl;
+  uint64_t ino;
+  barrier_interval iv;
+  enum CBlockSync_State state;
+  Barrier *barrier;
+  int *rval; /* see Cond.h */
+
+public:
+  boost::intrusive::list_member_hook<> intervals_hook;
+  C_Block_Sync(Client *c, uint64_t i, barrier_interval iv, int *r);
+  void finish(int rval);
+
+  friend class Barrier;
+  friend class BarrierContext;
+};
+
+C_Block_Sync::C_Block_Sync(Client *c, uint64_t i, barrier_interval iv,
+			   int *r=0) :
+  cl(c), ino(i), iv(iv), rval(r)
+{
+  state = CBlockSync_State_None;
+  barrier = NULL;
+
+  cldout(cl, 1) << "C_Block_Sync for " << ino << dendl;
+
+  if (!cl->barriers[ino]) {
+    cl->barriers[ino] = new BarrierContext(cl, ino);
+  }
+  /* XXX current semantics aren't commit-ordered */
+  cl->barriers[ino]->write_nobarrier(*this);
+}
+
+void C_Block_Sync::finish(int r) {
+  cldout(cl, 1) << "C_Block_Sync::finish() for " << ino << " "
+		<< iv << " r==" << r << dendl;
+  if (rval)
+    *rval = r;
+  cl->barriers[ino]->complete(*this);
+}
+
+/* Barrier */
+Barrier::Barrier()
+{ }
+
+Barrier::~Barrier()
+{ }
+
+/* BarrierContext */
+BarrierContext::BarrierContext(Client *c, uint64_t ino) :
+  cl(c), ino(ino), lock("BarrierContext")
+{ };
+
+void BarrierContext::write_nobarrier(C_Block_Sync &cbs)
+{
+  Mutex::Locker locker(lock);
+  cbs.state = CBlockSync_State_Unclaimed;
+  outstanding_writes.push_back(cbs);
+}
+
+void BarrierContext::write_barrier(C_Block_Sync &cbs)
+{
+  Mutex::Locker locker(lock);
+  barrier_interval &iv = cbs.iv;
+
+  { /* find blocking commit--intrusive no help here */
+    BarrierList::iterator iter;
+    bool done = false;
+    for (iter = active_commits.begin();
+	 !done && (iter != active_commits.end());
+	 ++iter) {
+      Barrier &barrier = *iter;
+      while (boost::icl::intersects(barrier.span, iv)) {
+	/*  wait on this */
+	barrier.cond.Wait(lock);
+	done = true;
+      }
+    }
+  }
+
+  cbs.state = CBlockSync_State_Unclaimed;
+  outstanding_writes.push_back(cbs);
+
+} /* write_barrier */
+
+void BarrierContext::commit_barrier(barrier_interval &civ)
+{
+    Mutex::Locker locker(lock);
+
+    /* we commit outstanding writes--if none exist, we don't care */
+    if (outstanding_writes.size() == 0)
+      return;
+
+    boost::icl::interval_set<uint64_t> cvs;
+    cvs.insert(civ);
+
+    Barrier *barrier = NULL;
+    BlockSyncList::iterator iter, iter2;
+
+    iter = outstanding_writes.begin();
+    while (iter != outstanding_writes.end()) {
+      barrier_interval &iv = iter->iv;
+      if (boost::icl::intersects(cvs, iv)) {
+	C_Block_Sync &a_write = *iter;
+	if (! barrier)
+	  barrier = new Barrier();
+	/* mark the callback */
+	a_write.state = CBlockSync_State_Committing;
+	a_write.barrier = barrier;
+	iter2 = iter++;
+	outstanding_writes.erase(iter2);
+	barrier->write_list.push_back(a_write);
+	barrier->span.insert(iv);
+	/* avoid iter invalidate */
+      } else {
+	++iter;
+      }
+    }
+
+    if (barrier) {
+      active_commits.push_back(*barrier);
+      /* and wait on this */
+      barrier->cond.Wait(lock);
+    }
+
+} /* commit_barrier */
+
+void BarrierContext::complete(C_Block_Sync &cbs)
+{
+    Mutex::Locker locker(lock);
+    BlockSyncList::iterator iter =
+      BlockSyncList::s_iterator_to(cbs);
+
+    switch (cbs.state) {
+    case CBlockSync_State_Unclaimed:
+      /* cool, no waiting */
+      outstanding_writes.erase(iter);
+      break;
+    case CBlockSync_State_Committing:
+    {
+      Barrier *barrier = iter->barrier;
+      barrier->write_list.erase(iter);
+      /* signal waiters */
+      barrier->cond.Signal();
+	/* dispose cleared barrier */
+      if (barrier->write_list.size() == 0) {
+	BarrierList::iterator iter2 =
+	  BarrierList::s_iterator_to(*barrier);
+	active_commits.erase(iter2);
+	delete barrier;
+      }
+    }
+    break;
+    default:
+      assert(false);
+      break;
+    }
+
+    cbs.state = CBlockSync_State_Completed;
+
+} /* complete */
+
+BarrierContext::~BarrierContext()
+{ }