Adding upstream version 14.2.21.upstream/14.2.21upstream

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

1 files changed, 3611 insertions, 0 deletions

diff --git a/src/mds/Migrator.cc b/src/mds/Migrator.cc
new file mode 100644
index 00000000..98bf78c3
--- /dev/null
+++ b/src/mds/Migrator.cc
@@ -0,0 +1,3611 @@
+// -*- 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 "CInode.h"
+#include "CDir.h"
+#include "CDentry.h"
+#include "Migrator.h"
+#include "Locker.h"
+#include "Server.h"
+
+#include "MDBalancer.h"
+#include "MDLog.h"
+#include "MDSMap.h"
+#include "Mutation.h"
+
+#include "include/filepath.h"
+#include "common/likely.h"
+
+#include "events/EExport.h"
+#include "events/EImportStart.h"
+#include "events/EImportFinish.h"
+#include "events/ESessions.h"
+
+#include "msg/Messenger.h"
+
+#include "messages/MClientCaps.h"
+
+/*
+ * this is what the dir->dir_auth values look like
+ *
+ *   dir_auth  authbits  
+ * export
+ *   me         me      - before
+ *   me, me     me      - still me, but preparing for export
+ *   me, them   me      - send MExportDir (peer is preparing)
+ *   them, me   me      - journaled EExport
+ *   them       them    - done
+ *
+ * import:
+ *   them       them    - before
+ *   me, them   me      - journaled EImportStart
+ *   me         me      - done
+ *
+ * which implies:
+ *  - auth bit is set if i am listed as first _or_ second dir_auth.
+ */
+
+#include "common/config.h"
+
+
+#define dout_context g_ceph_context
+#define dout_subsys ceph_subsys_mds
+#undef dout_prefix
+#define dout_prefix *_dout << "mds." << mds->get_nodeid() << ".migrator "
+
+
+class MigratorContext : public MDSContext {
+protected:
+  Migrator *mig;
+  MDSRank *get_mds() override {
+    return mig->mds;
+  }
+public:
+  explicit MigratorContext(Migrator *mig_) : mig(mig_) {
+    ceph_assert(mig != NULL);
+  }
+};
+
+class MigratorLogContext : public MDSLogContextBase {
+protected:
+  Migrator *mig;
+  MDSRank *get_mds() override {
+    return mig->mds;
+  }
+public:
+  explicit MigratorLogContext(Migrator *mig_) : mig(mig_) {
+    ceph_assert(mig != NULL);
+  }
+};
+
+void Migrator::dispatch(const Message::const_ref &m)
+{
+  switch (m->get_type()) {
+    // import
+  case MSG_MDS_EXPORTDIRDISCOVER:
+    handle_export_discover(MExportDirDiscover::msgref_cast(m));
+    break;
+  case MSG_MDS_EXPORTDIRPREP:
+    handle_export_prep(MExportDirPrep::msgref_cast(m));
+    break;
+  case MSG_MDS_EXPORTDIR:
+    if (unlikely(inject_session_race)) {
+      dout(0) << "waiting for inject_session_race" << dendl;
+      mds->wait_for_any_client_connection(new C_MDS_RetryMessage(mds, m));
+    } else {
+      handle_export_dir(MExportDir::msgref_cast(m));
+    }
+    break;
+  case MSG_MDS_EXPORTDIRFINISH:
+    handle_export_finish(MExportDirFinish::msgref_cast(m));
+    break;
+  case MSG_MDS_EXPORTDIRCANCEL:
+    handle_export_cancel(MExportDirCancel::msgref_cast(m));
+    break;
+
+    // export 
+  case MSG_MDS_EXPORTDIRDISCOVERACK:
+    handle_export_discover_ack(MExportDirDiscoverAck::msgref_cast(m));
+    break;
+  case MSG_MDS_EXPORTDIRPREPACK:
+    handle_export_prep_ack(MExportDirPrepAck::msgref_cast(m));
+    break;
+  case MSG_MDS_EXPORTDIRACK:
+    handle_export_ack(MExportDirAck::msgref_cast(m));
+    break;
+  case MSG_MDS_EXPORTDIRNOTIFYACK:
+    handle_export_notify_ack(MExportDirNotifyAck::msgref_cast(m));
+    break;
+
+    // export 3rd party (dir_auth adjustments)
+  case MSG_MDS_EXPORTDIRNOTIFY:
+    handle_export_notify(MExportDirNotify::msgref_cast(m));
+    break;
+
+    // caps
+  case MSG_MDS_EXPORTCAPS:
+    handle_export_caps(MExportCaps::msgref_cast(m));
+    break;
+  case MSG_MDS_EXPORTCAPSACK:
+    handle_export_caps_ack(MExportCapsAck::msgref_cast(m));
+    break;
+  case MSG_MDS_GATHERCAPS:
+    handle_gather_caps(MGatherCaps::msgref_cast(m));
+    break;
+
+  default:
+    derr << "migrator unknown message " << m->get_type() << dendl;
+    ceph_abort_msg("migrator unknown message");
+  }
+}
+
+
+class C_MDC_EmptyImport : public MigratorContext {
+  CDir *dir;
+public:
+  C_MDC_EmptyImport(Migrator *m, CDir *d) :
+    MigratorContext(m), dir(d) {
+    dir->get(CDir::PIN_PTRWAITER);
+  }
+  void finish(int r) override {
+    mig->export_empty_import(dir);
+    dir->put(CDir::PIN_PTRWAITER);
+  }
+};
+
+
+void Migrator::export_empty_import(CDir *dir)
+{
+  dout(7) << "export_empty_import " << *dir << dendl;
+  ceph_assert(dir->is_subtree_root());
+
+  if (dir->inode->is_auth()) {
+    dout(7) << " inode is auth" << dendl;
+    return;
+  }
+  if (!dir->is_auth()) {
+    dout(7) << " not auth" << dendl;
+    return;
+  }
+  if (dir->is_freezing() || dir->is_frozen()) {
+    dout(7) << " freezing or frozen" << dendl;
+    return;
+  }
+  if (dir->get_num_head_items() > 0) {
+    dout(7) << " not actually empty" << dendl;
+    return;
+  }
+  if (dir->inode->is_root()) {
+    dout(7) << " root" << dendl;
+    return;
+  }
+  
+  mds_rank_t dest = dir->inode->authority().first;
+  //if (mds->is_shutting_down()) dest = 0;  // this is more efficient.
+  
+  dout(7) << " really empty, exporting to " << dest << dendl;
+  assert (dest != mds->get_nodeid());
+  
+  dout(7) << "exporting to mds." << dest 
+           << " empty import " << *dir << dendl;
+  export_dir( dir, dest );
+}
+
+void Migrator::find_stale_export_freeze()
+{
+  utime_t now = ceph_clock_now();
+  utime_t cutoff = now;
+  cutoff -= g_conf()->mds_freeze_tree_timeout;
+
+
+  /*
+   * We could have situations like:
+   *
+   * - mds.0 authpins an item in subtree A
+   * - mds.0 sends request to mds.1 to authpin an item in subtree B
+   * - mds.0 freezes subtree A
+   * - mds.1 authpins an item in subtree B
+   * - mds.1 sends request to mds.0 to authpin an item in subtree A
+   * - mds.1 freezes subtree B
+   * - mds.1 receives the remote authpin request from mds.0
+   *   (wait because subtree B is freezing)
+   * - mds.0 receives the remote authpin request from mds.1
+   *   (wait because subtree A is freezing)
+   *
+   *
+   * - client request authpins items in subtree B
+   * - freeze subtree B
+   * - import subtree A which is parent of subtree B
+   *   (authpins parent inode of subtree B, see CDir::set_dir_auth())
+   * - freeze subtree A
+   * - client request tries authpinning items in subtree A
+   *   (wait because subtree A is freezing)
+   */
+  for (map<CDir*,export_state_t>::iterator p = export_state.begin();
+       p != export_state.end(); ) {
+    CDir* dir = p->first;
+    export_state_t& stat = p->second;
+    ++p;
+    if (stat.state != EXPORT_DISCOVERING && stat.state != EXPORT_FREEZING)
+      continue;
+    ceph_assert(dir->freeze_tree_state);
+    if (stat.last_cum_auth_pins != dir->freeze_tree_state->auth_pins) {
+      stat.last_cum_auth_pins = dir->freeze_tree_state->auth_pins;
+      stat.last_cum_auth_pins_change = now;
+      continue;
+    }
+    if (stat.last_cum_auth_pins_change >= cutoff)
+      continue;
+    if (stat.num_remote_waiters > 0 ||
+	(!dir->inode->is_root() && dir->get_parent_dir()->is_freezing())) {
+      export_try_cancel(dir);
+    }
+  }
+}
+
+void Migrator::export_try_cancel(CDir *dir, bool notify_peer)
+{
+  dout(10) << "export_try_cancel " << *dir << dendl;
+
+  map<CDir*,export_state_t>::iterator it = export_state.find(dir);
+  ceph_assert(it != export_state.end());
+
+  int state = it->second.state;
+  switch (state) {
+  case EXPORT_LOCKING:
+    dout(10) << "export state=locking : dropping locks and removing auth_pin" << dendl;
+    num_locking_exports--;
+    it->second.state = EXPORT_CANCELLED;
+    dir->auth_unpin(this);
+    break;
+  case EXPORT_DISCOVERING:
+    dout(10) << "export state=discovering : canceling freeze and removing auth_pin" << dendl;
+    it->second.state = EXPORT_CANCELLED;
+    dir->unfreeze_tree();  // cancel the freeze
+    dir->auth_unpin(this);
+    if (notify_peer &&
+	(!mds->is_cluster_degraded() ||
+	 mds->mdsmap->is_clientreplay_or_active_or_stopping(it->second.peer))) // tell them.
+      mds->send_message_mds(MExportDirCancel::create(dir->dirfrag(), it->second.tid), it->second.peer);
+    break;
+
+  case EXPORT_FREEZING:
+    dout(10) << "export state=freezing : canceling freeze" << dendl;
+    it->second.state = EXPORT_CANCELLED;
+    dir->unfreeze_tree();  // cancel the freeze
+    if (dir->is_subtree_root())
+      cache->try_subtree_merge(dir);
+    if (notify_peer &&
+	(!mds->is_cluster_degraded() ||
+	 mds->mdsmap->is_clientreplay_or_active_or_stopping(it->second.peer))) // tell them.
+      mds->send_message_mds(MExportDirCancel::create(dir->dirfrag(), it->second.tid), it->second.peer);
+    break;
+
+    // NOTE: state order reversal, warning comes after prepping
+  case EXPORT_WARNING:
+    dout(10) << "export state=warning : unpinning bounds, unfreezing, notifying" << dendl;
+    it->second.state = EXPORT_CANCELLING;
+    // fall-thru
+
+  case EXPORT_PREPPING:
+    if (state != EXPORT_WARNING) {
+      dout(10) << "export state=prepping : unpinning bounds, unfreezing" << dendl;
+      it->second.state = EXPORT_CANCELLED;
+    }
+
+    {
+      // unpin bounds
+      set<CDir*> bounds;
+      cache->get_subtree_bounds(dir, bounds);
+      for (set<CDir*>::iterator q = bounds.begin();
+          q != bounds.end();
+          ++q) {
+        CDir *bd = *q;
+        bd->put(CDir::PIN_EXPORTBOUND);
+        bd->state_clear(CDir::STATE_EXPORTBOUND);
+      }
+      if (state == EXPORT_WARNING) {
+	// notify bystanders
+	export_notify_abort(dir, it->second, bounds);
+	// process delayed expires
+	cache->process_delayed_expire(dir);
+      }
+    }
+    dir->unfreeze_tree();
+    cache->try_subtree_merge(dir);
+    if (notify_peer &&
+	(!mds->is_cluster_degraded() ||
+	 mds->mdsmap->is_clientreplay_or_active_or_stopping(it->second.peer))) // tell them.
+      mds->send_message_mds(MExportDirCancel::create(dir->dirfrag(), it->second.tid), it->second.peer);
+    break;
+
+  case EXPORT_EXPORTING:
+    dout(10) << "export state=exporting : reversing, and unfreezing" << dendl;
+    it->second.state = EXPORT_CANCELLING;
+    export_reverse(dir, it->second);
+    break;
+
+  case EXPORT_LOGGINGFINISH:
+  case EXPORT_NOTIFYING:
+    dout(10) << "export state=loggingfinish|notifying : ignoring dest failure, we were successful." << dendl;
+    // leave export_state, don't clean up now.
+    break;
+  case EXPORT_CANCELLING:
+    break;
+
+  default:
+    ceph_abort();
+  }
+
+  // finish clean-up?
+  if (it->second.state == EXPORT_CANCELLING ||
+      it->second.state == EXPORT_CANCELLED) {
+    MutationRef mut;
+    mut.swap(it->second.mut);
+
+    if (it->second.state == EXPORT_CANCELLED) {
+      export_cancel_finish(it);
+    }
+
+    // drop locks
+    if (state == EXPORT_LOCKING || state == EXPORT_DISCOVERING) {
+      MDRequestRef mdr = static_cast<MDRequestImpl*>(mut.get());
+      ceph_assert(mdr);
+      mds->mdcache->request_kill(mdr);
+    } else if (mut) {
+      mds->locker->drop_locks(mut.get());
+      mut->cleanup();
+    }
+
+    cache->show_subtrees();
+
+    maybe_do_queued_export();
+  }
+}
+
+void Migrator::export_cancel_finish(export_state_iterator& it)
+{
+  CDir *dir = it->first;
+  bool unpin = (it->second.state == EXPORT_CANCELLING);
+  auto parent = std::move(it->second.parent);
+
+  total_exporting_size -= it->second.approx_size;
+  export_state.erase(it);
+
+  ceph_assert(dir->state_test(CDir::STATE_EXPORTING));
+  dir->clear_exporting();
+
+  if (unpin) {
+    // pinned by Migrator::export_notify_abort()
+    dir->auth_unpin(this);
+  }
+  // send pending import_maps?  (these need to go out when all exports have finished.)
+  cache->maybe_send_pending_resolves();
+
+  if (parent)
+    child_export_finish(parent, false);
+}
+
+// ==========================================================
+// mds failure handling
+
+void Migrator::handle_mds_failure_or_stop(mds_rank_t who)
+{
+  dout(5) << "handle_mds_failure_or_stop mds." << who << dendl;
+
+  // check my exports
+
+  // first add an extra auth_pin on any freezes, so that canceling a
+  // nested freeze doesn't complete one further up the hierarchy and
+  // confuse the shit out of us.  we'll remove it after canceling the
+  // freeze.  this way no freeze completions run before we want them
+  // to.
+  list<CDir*> pinned_dirs;
+  for (map<CDir*,export_state_t>::iterator p = export_state.begin();
+       p != export_state.end();
+       ++p) {
+    if (p->second.state == EXPORT_FREEZING) {
+      CDir *dir = p->first;
+      dout(10) << "adding temp auth_pin on freezing " << *dir << dendl;
+      dir->auth_pin(this);
+      pinned_dirs.push_back(dir);
+    }
+  }
+
+  map<CDir*,export_state_t>::iterator p = export_state.begin();
+  while (p != export_state.end()) {
+    map<CDir*,export_state_t>::iterator next = p;
+    ++next;
+    CDir *dir = p->first;
+    
+    // abort exports:
+    //  - that are going to the failed node
+    //  - that aren't frozen yet (to avoid auth_pin deadlock)
+    //  - they havne't prepped yet (they may need to discover bounds to do that)
+    if ((p->second.peer == who &&
+	 p->second.state != EXPORT_CANCELLING) ||
+	p->second.state == EXPORT_LOCKING ||
+	p->second.state == EXPORT_DISCOVERING ||
+	p->second.state == EXPORT_FREEZING ||
+	p->second.state == EXPORT_PREPPING) {
+      // the guy i'm exporting to failed, or we're just freezing.
+      dout(10) << "cleaning up export state (" << p->second.state << ")"
+	       << get_export_statename(p->second.state) << " of " << *dir << dendl;
+      export_try_cancel(dir);
+    } else if (p->second.peer != who) {
+      // bystander failed.
+      if (p->second.warning_ack_waiting.erase(who)) {
+	if (p->second.state == EXPORT_WARNING) {
+	  p->second.notify_ack_waiting.erase(who);   // they won't get a notify either.
+	  // exporter waiting for warning acks, let's fake theirs.
+	  dout(10) << "faking export_warning_ack from mds." << who
+		   << " on " << *dir << " to mds." << p->second.peer
+		   << dendl;
+	  if (p->second.warning_ack_waiting.empty())
+	    export_go(dir);
+	}
+      }
+      if (p->second.notify_ack_waiting.erase(who)) {
+	// exporter is waiting for notify acks, fake it
+	dout(10) << "faking export_notify_ack from mds." << who
+		 << " on " << *dir << " to mds." << p->second.peer
+		 << dendl;
+	if (p->second.state == EXPORT_NOTIFYING) {
+	  if (p->second.notify_ack_waiting.empty())
+	    export_finish(dir);
+	} else if (p->second.state == EXPORT_CANCELLING) {
+	  if (p->second.notify_ack_waiting.empty()) {
+	    export_cancel_finish(p);
+	  }
+	}
+      }
+    }
+    
+    // next!
+    p = next;
+  }
+
+
+  // check my imports
+  map<dirfrag_t,import_state_t>::iterator q = import_state.begin();
+  while (q != import_state.end()) {
+    map<dirfrag_t,import_state_t>::iterator next = q;
+    ++next;
+    dirfrag_t df = q->first;
+    CInode *diri = mds->mdcache->get_inode(df.ino);
+    CDir *dir = mds->mdcache->get_dirfrag(df);
+
+    if (q->second.peer == who) {
+      if (dir)
+	dout(10) << "cleaning up import state (" << q->second.state << ")"
+		 << get_import_statename(q->second.state) << " of " << *dir << dendl;
+      else
+	dout(10) << "cleaning up import state (" << q->second.state << ")"
+		 << get_import_statename(q->second.state) << " of " << df << dendl;
+
+      switch (q->second.state) {
+      case IMPORT_DISCOVERING:
+	dout(10) << "import state=discovering : clearing state" << dendl;
+	import_reverse_discovering(df);
+	break;
+
+      case IMPORT_DISCOVERED:
+	ceph_assert(diri);
+	dout(10) << "import state=discovered : unpinning inode " << *diri << dendl;
+	import_reverse_discovered(df, diri);
+	break;
+
+      case IMPORT_PREPPING:
+	ceph_assert(dir);
+	dout(10) << "import state=prepping : unpinning base+bounds " << *dir << dendl;
+	import_reverse_prepping(dir, q->second);
+	break;
+
+      case IMPORT_PREPPED:
+	ceph_assert(dir);
+	dout(10) << "import state=prepped : unpinning base+bounds, unfreezing " << *dir << dendl;
+	{
+	  set<CDir*> bounds;
+	  cache->get_subtree_bounds(dir, bounds);
+	  import_remove_pins(dir, bounds);
+	  
+	  // adjust auth back to the exporter
+	  cache->adjust_subtree_auth(dir, q->second.peer);
+
+	  // notify bystanders ; wait in aborting state
+	  q->second.state = IMPORT_ABORTING;
+	  import_notify_abort(dir, bounds);
+	  ceph_assert(g_conf()->mds_kill_import_at != 10);
+	}
+	break;
+
+      case IMPORT_LOGGINGSTART:
+	ceph_assert(dir);
+	dout(10) << "import state=loggingstart : reversing import on " << *dir << dendl;
+	import_reverse(dir);
+	break;
+
+      case IMPORT_ACKING:
+	ceph_assert(dir);
+	// hrm.  make this an ambiguous import, and wait for exporter recovery to disambiguate
+	dout(10) << "import state=acking : noting ambiguous import " << *dir << dendl;
+	{
+	  set<CDir*> bounds;
+	  cache->get_subtree_bounds(dir, bounds);
+	  cache->add_ambiguous_import(dir, bounds);
+	}
+	break;
+	
+      case IMPORT_FINISHING:
+	ceph_assert(dir);
+	dout(10) << "import state=finishing : finishing import on " << *dir << dendl;
+	import_finish(dir, true);
+	break;
+
+      case IMPORT_ABORTING:
+	ceph_assert(dir);
+	dout(10) << "import state=aborting : ignoring repeat failure " << *dir << dendl;
+	break;
+      }
+    } else {
+      auto bystanders_entry = q->second.bystanders.find(who);
+      if (bystanders_entry != q->second.bystanders.end()) {
+	q->second.bystanders.erase(bystanders_entry);
+	if (q->second.state == IMPORT_ABORTING) {
+	  ceph_assert(dir);
+	  dout(10) << "faking export_notify_ack from mds." << who
+		   << " on aborting import " << *dir << " from mds." << q->second.peer
+		   << dendl;
+	  if (q->second.bystanders.empty())
+	    import_reverse_unfreeze(dir);
+	}
+      }
+    }
+
+    // next!
+    q = next;
+  }
+
+  while (!pinned_dirs.empty()) {
+    CDir *dir = pinned_dirs.front();
+    dout(10) << "removing temp auth_pin on " << *dir << dendl;
+    dir->auth_unpin(this);
+    pinned_dirs.pop_front();
+  }  
+}
+
+
+
+void Migrator::show_importing()
+{  
+  dout(10) << "show_importing" << dendl;
+  for (map<dirfrag_t,import_state_t>::iterator p = import_state.begin();
+       p != import_state.end();
+       ++p) {
+    CDir *dir = mds->mdcache->get_dirfrag(p->first);
+    if (dir) {
+      dout(10) << " importing from " << p->second.peer
+	       << ": (" << p->second.state << ") " << get_import_statename(p->second.state)
+	       << " " << p->first << " " << *dir << dendl;
+    } else {
+      dout(10) << " importing from " << p->second.peer
+	       << ": (" << p->second.state << ") " << get_import_statename(p->second.state)
+	       << " " << p->first << dendl;
+    }
+  }
+}
+
+void Migrator::show_exporting() 
+{
+  dout(10) << "show_exporting" << dendl;
+  for (map<CDir*,export_state_t>::iterator p = export_state.begin();
+       p != export_state.end();
+       ++p) 
+    dout(10) << " exporting to " << p->second.peer
+	     << ": (" << p->second.state << ") " << get_export_statename(p->second.state)
+	     << " " << p->first->dirfrag() << " " << *p->first << dendl;
+}
+
+
+
+void Migrator::audit()
+{
+  if (!g_conf()->subsys.should_gather<ceph_subsys_mds, 5>())
+    return;  // hrm.
+
+  // import_state
+  show_importing();
+  for (map<dirfrag_t,import_state_t>::iterator p = import_state.begin();
+       p != import_state.end();
+       ++p) {
+    if (p->second.state == IMPORT_DISCOVERING)
+      continue;
+    if (p->second.state == IMPORT_DISCOVERED) {
+      CInode *in = cache->get_inode(p->first.ino);
+      ceph_assert(in);
+      continue;
+    }
+    CDir *dir = cache->get_dirfrag(p->first);
+    ceph_assert(dir);
+    if (p->second.state == IMPORT_PREPPING)
+      continue;
+    if (p->second.state == IMPORT_ABORTING) {
+      ceph_assert(!dir->is_ambiguous_dir_auth());
+      ceph_assert(dir->get_dir_auth().first != mds->get_nodeid());
+      continue;
+    }
+    ceph_assert(dir->is_ambiguous_dir_auth());
+    ceph_assert(dir->authority().first  == mds->get_nodeid() ||
+	   dir->authority().second == mds->get_nodeid());
+  }
+
+  // export_state
+  show_exporting();
+  for (map<CDir*,export_state_t>::iterator p = export_state.begin();
+       p != export_state.end();
+       ++p) {
+    CDir *dir = p->first;
+    if (p->second.state == EXPORT_LOCKING ||
+	p->second.state == EXPORT_DISCOVERING ||
+	p->second.state == EXPORT_FREEZING ||
+	p->second.state == EXPORT_CANCELLING)
+      continue;
+    ceph_assert(dir->is_ambiguous_dir_auth());
+    ceph_assert(dir->authority().first  == mds->get_nodeid() ||
+	   dir->authority().second == mds->get_nodeid());
+  }
+
+  // ambiguous+me subtrees should be importing|exporting
+
+  // write me
+}
+
+
+
+
+
+// ==========================================================
+// EXPORT
+
+void Migrator::export_dir_nicely(CDir *dir, mds_rank_t dest)
+{
+  // enqueue
+  dout(7) << "export_dir_nicely " << *dir << " to " << dest << dendl;
+  export_queue.push_back(pair<dirfrag_t,mds_rank_t>(dir->dirfrag(), dest));
+
+  maybe_do_queued_export();
+}
+
+void Migrator::maybe_do_queued_export()
+{
+  static bool running;
+  if (running)
+    return;
+  running = true;
+
+  uint64_t max_total_size = max_export_size * 2;
+
+  while (!export_queue.empty() &&
+	 max_total_size > total_exporting_size &&
+	 max_total_size - total_exporting_size >=
+	 max_export_size * (num_locking_exports + 1)) {
+
+    dirfrag_t df = export_queue.front().first;
+    mds_rank_t dest = export_queue.front().second;
+    export_queue.pop_front();
+    
+    CDir *dir = mds->mdcache->get_dirfrag(df);
+    if (!dir) continue;
+    if (!dir->is_auth()) continue;
+
+    dout(0) << "nicely exporting to mds." << dest << " " << *dir << dendl;
+
+    export_dir(dir, dest);
+  }
+
+  running = false;
+}
+
+
+
+
+class C_MDC_ExportFreeze : public MigratorContext {
+  CDir *dir;   // dir i'm exporting
+  uint64_t tid;
+public:
+  C_MDC_ExportFreeze(Migrator *m, CDir *e, uint64_t t) :
+    MigratorContext(m), dir(e), tid(t) {
+    dir->get(CDir::PIN_PTRWAITER);
+  }
+  void finish(int r) override {
+    if (r >= 0)
+      mig->export_frozen(dir, tid);
+    dir->put(CDir::PIN_PTRWAITER);
+  }
+};
+
+
+void Migrator::get_export_lock_set(CDir *dir, MutationImpl::LockOpVec& lov)
+{
+  // path
+  vector<CDentry*> trace;
+  cache->make_trace(trace, dir->inode);
+
+  set<CDir*> wouldbe_bounds;
+  cache->get_wouldbe_subtree_bounds(dir, wouldbe_bounds);
+
+  lov.reserve(trace.size() + wouldbe_bounds.size() + 8);
+
+  for (auto& dn : trace)
+    lov.add_rdlock(&dn->lock);
+
+  // prevent scatter gather race
+  lov.add_rdlock(&dir->get_inode()->dirfragtreelock);
+
+  // bound dftlocks:
+  // NOTE: We need to take an rdlock on bounding dirfrags during
+  //  migration for a rather irritating reason: when we export the
+  //  bound inode, we need to send scatterlock state for the dirfrags
+  //  as well, so that the new auth also gets the correct info.  If we
+  //  race with a refragment, this info is useless, as we can't
+  //  redivvy it up.  And it's needed for the scatterlocks to work
+  //  properly: when the auth is in a sync/lock state it keeps each
+  //  dirfrag's portion in the local (auth OR replica) dirfrag.
+  for (auto& dir : wouldbe_bounds)
+    lov.add_rdlock(&dir->get_inode()->dirfragtreelock);
+
+  // above code may add duplicated locks
+  lov.sort_and_merge();
+}
+
+
+/** export_dir(dir, dest)
+ * public method to initiate an export.
+ * will fail if the directory is freezing, frozen, unpinnable, or root. 
+ */
+void Migrator::export_dir(CDir *dir, mds_rank_t dest)
+{
+  dout(7) << "export_dir " << *dir << " to " << dest << dendl;
+  ceph_assert(dir->is_auth());
+  ceph_assert(dest != mds->get_nodeid());
+   
+  if (!mds->is_stopping() && !dir->inode->is_exportable(dest)) {
+    dout(25) << "dir is export pinned" << dendl;
+    return;
+  }
+
+  if (!(mds->is_active() || mds->is_stopping())) {
+    dout(7) << "i'm not active, no exports for now" << dendl;
+    return;
+  }
+  if (mds->mdcache->is_readonly()) {
+    dout(7) << "read-only FS, no exports for now" << dendl;
+    return;
+  }
+  if (!mds->mdsmap->is_active(dest)) {
+    dout(7) << "dest not active, no exports for now" << dendl;
+    return;
+  }
+  if (mds->is_cluster_degraded()) {
+    dout(7) << "cluster degraded, no exports for now" << dendl;
+    return;
+  }
+  if (dir->inode->is_system()) {
+    dout(7) << "i won't export system dirs (root, mdsdirs, stray, /.ceph, etc.)" << dendl;
+    //ceph_abort();
+    return;
+  }
+
+  CDir* parent_dir = dir->inode->get_projected_parent_dir();
+  if (parent_dir && parent_dir->inode->is_stray()) {
+    if (parent_dir->get_parent_dir()->ino() != MDS_INO_MDSDIR(dest)) {
+      dout(7) << "i won't export anything in stray" << dendl;
+      return;
+    }
+  }
+
+  if (dir->is_frozen() ||
+      dir->is_freezing()) {
+    dout(7) << " can't export, freezing|frozen.  wait for other exports to finish first." << dendl;
+    return;
+  }
+  if (dir->state_test(CDir::STATE_EXPORTING)) {
+    dout(7) << "already exporting" << dendl;
+    return;
+  }
+
+  if (g_conf()->mds_thrash_exports) {
+    // create random subtree bound (which will not be exported)
+    list<CDir*> ls;
+    for (auto p = dir->begin(); p != dir->end(); ++p) {
+      auto dn = p->second;
+      CDentry::linkage_t *dnl= dn->get_linkage();
+      if (dnl->is_primary()) {
+	CInode *in = dnl->get_inode();
+	if (in->is_dir())
+	  in->get_nested_dirfrags(ls);
+      }
+    }
+    if (ls.size() > 0) {
+      int n = rand() % ls.size();
+      auto p = ls.begin();
+      while (n--) ++p;
+      CDir *bd = *p;
+      if (!(bd->is_frozen() || bd->is_freezing())) {
+	ceph_assert(bd->is_auth());
+	dir->state_set(CDir::STATE_AUXSUBTREE);
+	mds->mdcache->adjust_subtree_auth(dir, mds->get_nodeid());
+	dout(0) << "export_dir: create aux subtree " << *bd << " under " << *dir << dendl;
+      }
+    }
+  }
+
+  mds->hit_export_target(dest, -1);
+
+  dir->auth_pin(this);
+  dir->mark_exporting();
+
+  MDRequestRef mdr = mds->mdcache->request_start_internal(CEPH_MDS_OP_EXPORTDIR);
+  mdr->more()->export_dir = dir;
+  mdr->pin(dir);
+
+  ceph_assert(export_state.count(dir) == 0);
+  export_state_t& stat = export_state[dir];
+  num_locking_exports++;
+  stat.state = EXPORT_LOCKING;
+  stat.peer = dest;
+  stat.tid = mdr->reqid.tid;
+  stat.mut = mdr;
+
+  mds->mdcache->dispatch_request(mdr);
+}
+
+/*
+ * check if directory is too large to be export in whole. If it is,
+ * choose some subdirs, whose total size is suitable.
+ */
+void Migrator::maybe_split_export(CDir* dir, uint64_t max_size, bool null_okay,
+				  vector<pair<CDir*, size_t> >& results)
+{
+  static const unsigned frag_size = 800;
+  static const unsigned inode_size = 1000;
+  static const unsigned cap_size = 80;
+  static const unsigned remote_size = 10;
+  static const unsigned null_size = 1;
+
+  // state for depth-first search
+  struct LevelData {
+    CDir *dir;
+    CDir::dentry_key_map::iterator iter;
+    size_t dirfrag_size = frag_size;
+    size_t subdirs_size = 0;
+    bool complete = true;
+    vector<CDir*> siblings;
+    vector<pair<CDir*, size_t> > subdirs;
+    LevelData(const LevelData&) = default;
+    LevelData(CDir *d) :
+      dir(d), iter(d->begin()) {}
+  };
+
+  vector<LevelData> stack;
+  stack.emplace_back(dir);
+
+  size_t found_size = 0;
+  size_t skipped_size = 0;
+
+  for (;;) {
+    auto& data = stack.back();
+    CDir *cur = data.dir;
+    auto& it = data.iter;
+    auto& dirfrag_size = data.dirfrag_size;
+
+    while(it != cur->end()) {
+      CDentry *dn = it->second;
+      ++it;
+
+      dirfrag_size += dn->name.size();
+      if (dn->get_linkage()->is_null()) {
+	dirfrag_size += null_size;
+	continue;
+      }
+      if (dn->get_linkage()->is_remote()) {
+	dirfrag_size += remote_size;
+	continue;
+      }
+
+      CInode *in = dn->get_linkage()->get_inode();
+      dirfrag_size += inode_size;
+      dirfrag_size += in->get_client_caps().size() * cap_size;
+
+      if (in->is_dir()) {
+	vector<CDir*> ls;
+	in->get_nested_dirfrags(ls);
+	std::reverse(ls.begin(), ls.end());
+
+	bool complete = true;
+	for (auto p = ls.begin(); p != ls.end(); ) {
+	  if ((*p)->state_test(CDir::STATE_EXPORTING) ||
+	      (*p)->is_freezing_dir() || (*p)->is_frozen_dir()) {
+	    complete = false;
+	    p = ls.erase(p);
+	  } else {
+	    ++p;
+	  }
+	}
+	if (!complete) {
+	  // skip exporting dir's ancestors. because they can't get
+	  // frozen (exporting dir's parent inode is auth pinned).
+	  for (auto p = stack.rbegin(); p < stack.rend(); ++p) {
+	    if (!p->complete)
+	      break;
+	    p->complete = false;
+	  }
+	}
+	if (!ls.empty()) {
+	  stack.emplace_back(ls.back());
+	  ls.pop_back();
+	  stack.back().siblings.swap(ls);
+	  break;
+	}
+      }
+    }
+    // did above loop push new dirfrag into the stack?
+    if (stack.back().dir != cur)
+      continue;
+
+    if (data.complete) {
+      auto cur_size = data.subdirs_size + dirfrag_size;
+      // we can do nothing with large dirfrag
+      if (cur_size >= max_size && found_size * 2 > max_size)
+	break;
+
+      found_size += dirfrag_size;
+
+      if (stack.size() > 1) {
+	auto& parent = stack[stack.size() - 2];
+	parent.subdirs.emplace_back(cur, cur_size);
+	parent.subdirs_size += cur_size;
+      }
+    } else {
+      // can't merge current dirfrag to its parent if there is skipped subdir
+      results.insert(results.end(), data.subdirs.begin(), data.subdirs.end());
+      skipped_size += dirfrag_size;
+    }
+
+    vector<CDir*> ls;
+    ls.swap(data.siblings);
+
+    stack.pop_back();
+    if (stack.empty())
+      break;
+
+    if (found_size >= max_size)
+      break;
+
+    // next dirfrag
+    if (!ls.empty()) {
+      stack.emplace_back(ls.back());
+      ls.pop_back();
+      stack.back().siblings.swap(ls);
+    }
+  }
+
+  for (auto& p : stack)
+    results.insert(results.end(), p.subdirs.begin(), p.subdirs.end());
+
+  if (results.empty() && (!skipped_size || !null_okay))
+    results.emplace_back(dir, found_size + skipped_size);
+}
+
+class C_M_ExportDirWait : public MigratorContext {
+  MDRequestRef mdr;
+  int count;
+public:
+  C_M_ExportDirWait(Migrator *m, MDRequestRef mdr, int count)
+    : MigratorContext(m), mdr(mdr), count(count) {}
+  void finish(int r) override {
+    mig->dispatch_export_dir(mdr, count);
+  }
+};
+
+void Migrator::dispatch_export_dir(MDRequestRef& mdr, int count)
+{
+  CDir *dir = mdr->more()->export_dir;
+  dout(7) << "dispatch_export_dir " << *mdr << " " << *dir << dendl;
+
+  map<CDir*,export_state_t>::iterator it = export_state.find(dir);
+  if (it == export_state.end() || it->second.tid != mdr->reqid.tid) {
+    // export must have aborted.
+    dout(7) << "export must have aborted " << *mdr << dendl;
+    ceph_assert(mdr->killed || mdr->aborted);
+    if (mdr->aborted) {
+      mdr->aborted = false;
+      mds->mdcache->request_kill(mdr);
+    }
+    return;
+  }
+  ceph_assert(it->second.state == EXPORT_LOCKING);
+
+  mds_rank_t dest = it->second.peer;
+
+  if (!mds->is_export_target(dest)) {
+    dout(7) << "dest is not yet an export target" << dendl;
+    if (count > 3) {
+      dout(5) << "dest has not been added as export target after three MDSMap epochs, canceling export" << dendl;
+      export_try_cancel(dir);
+      return;
+    }
+
+    mds->locker->drop_locks(mdr.get());
+    mdr->drop_local_auth_pins();
+
+    mds->wait_for_mdsmap(mds->mdsmap->get_epoch(), new C_M_ExportDirWait(this, mdr, count+1));
+    return;
+  }
+
+  if (!dir->inode->get_parent_dn()) {
+    dout(7) << "waiting for dir to become stable before export: " << *dir << dendl;
+    dir->add_waiter(CDir::WAIT_CREATED, new C_M_ExportDirWait(this, mdr, 1));
+    return;
+  }
+
+  if (mdr->aborted || dir->is_frozen() || dir->is_freezing()) {
+    dout(7) << "wouldblock|freezing|frozen, canceling export" << dendl;
+    export_try_cancel(dir);
+    return;
+  }
+
+  // locks?
+  MutationImpl::LockOpVec lov;
+  get_export_lock_set(dir, lov);
+  // If auth MDS of the subtree root inode is neither the exporter MDS
+  // nor the importer MDS and it gathers subtree root's fragstat/neststat
+  // while the subtree is exporting. It's possible that the exporter MDS
+  // and the importer MDS both are auth MDS of the subtree root or both
+  // are not auth MDS of the subtree root at the time they receive the
+  // lock messages. So the auth MDS of the subtree root inode may get no
+  // or duplicated fragstat/neststat for the subtree root dirfrag.
+  lov.add_wrlock(&dir->get_inode()->filelock);
+  lov.add_wrlock(&dir->get_inode()->nestlock);
+  if (dir->get_inode()->is_auth()) {
+    dir->get_inode()->filelock.set_scatter_wanted();
+    dir->get_inode()->nestlock.set_scatter_wanted();
+  }
+
+  if (!mds->locker->acquire_locks(mdr, lov, NULL, true)) {
+    if (mdr->aborted)
+      export_try_cancel(dir);
+    return;
+  }
+
+  ceph_assert(g_conf()->mds_kill_export_at != 1);
+
+  auto parent = it->second.parent;
+
+  vector<pair<CDir*, size_t> > results;
+  maybe_split_export(dir, max_export_size, (bool)parent, results);
+
+  if (results.size() == 1 && results.front().first == dir) {
+    num_locking_exports--;
+    it->second.state = EXPORT_DISCOVERING;
+    // send ExportDirDiscover (ask target)
+    filepath path;
+    dir->inode->make_path(path);
+    auto discover = MExportDirDiscover::create(dir->dirfrag(), path,
+					       mds->get_nodeid(), it->second.tid);
+    mds->send_message_mds(discover, dest);
+    ceph_assert(g_conf()->mds_kill_export_at != 2);
+
+    it->second.last_cum_auth_pins_change = ceph_clock_now();
+    it->second.approx_size = results.front().second;
+    total_exporting_size += it->second.approx_size;
+
+    // start the freeze, but hold it up with an auth_pin.
+    dir->freeze_tree();
+    ceph_assert(dir->is_freezing_tree());
+    dir->add_waiter(CDir::WAIT_FROZEN, new C_MDC_ExportFreeze(this, dir, it->second.tid));
+    return;
+  }
+
+  if (parent) {
+    parent->pending_children += results.size();
+  } else {
+    parent = std::make_shared<export_base_t>(dir->dirfrag(), dest,
+					     results.size(), export_queue_gen);
+  }
+
+  if (results.empty()) {
+    dout(7) << "subtree's children all are under exporting, retry rest parts of parent export "
+	    << parent->dirfrag << dendl;
+    parent->restart = true;
+  } else {
+    dout(7) << "subtree is too large, splitting it into: " <<  dendl;
+  }
+
+  for (auto& p : results) {
+    CDir *sub = p.first;
+    ceph_assert(sub != dir);
+    dout(7) << " sub " << *sub << dendl;
+
+    sub->auth_pin(this);
+    sub->mark_exporting();
+
+    MDRequestRef _mdr = mds->mdcache->request_start_internal(CEPH_MDS_OP_EXPORTDIR);
+    _mdr->more()->export_dir = sub;
+    _mdr->pin(sub);
+
+    ceph_assert(export_state.count(sub) == 0);
+    auto& stat = export_state[sub];
+    num_locking_exports++;
+    stat.state = EXPORT_LOCKING;
+    stat.peer = dest;
+    stat.tid = _mdr->reqid.tid;
+    stat.mut = _mdr;
+    stat.parent = parent;
+    mds->mdcache->dispatch_request(_mdr);
+  }
+
+  // cancel the original one
+  export_try_cancel(dir);
+}
+
+void Migrator::child_export_finish(std::shared_ptr<export_base_t>& parent, bool success)
+{
+  if (success)
+    parent->restart = true;
+  if (--parent->pending_children == 0) {
+    if (parent->restart &&
+	parent->export_queue_gen == export_queue_gen) {
+      CDir *origin = mds->mdcache->get_dirfrag(parent->dirfrag);
+      if (origin && origin->is_auth()) {
+	dout(7) << "child_export_finish requeue " << *origin << dendl;
+	export_queue.emplace_front(origin->dirfrag(), parent->dest);
+      }
+    }
+  }
+}
+
+/*
+ * called on receipt of MExportDirDiscoverAck
+ * the importer now has the directory's _inode_ in memory, and pinned.
+ */
+void Migrator::handle_export_discover_ack(const MExportDirDiscoverAck::const_ref &m)
+{
+  CDir *dir = cache->get_dirfrag(m->get_dirfrag());
+  mds_rank_t dest(m->get_source().num());
+  ceph_assert(dir);
+  
+  dout(7) << "export_discover_ack from " << m->get_source()
+	  << " on " << *dir << dendl;
+
+  mds->hit_export_target(dest, -1);
+
+  map<CDir*,export_state_t>::iterator it = export_state.find(dir);
+  if (it == export_state.end() ||
+      it->second.tid != m->get_tid() ||
+      it->second.peer != dest) {
+    dout(7) << "must have aborted" << dendl;
+  } else {
+    ceph_assert(it->second.state == EXPORT_DISCOVERING);
+
+    if (m->is_success()) {
+      // release locks to avoid deadlock
+      MDRequestRef mdr = static_cast<MDRequestImpl*>(it->second.mut.get());
+      ceph_assert(mdr);
+      mds->mdcache->request_finish(mdr);
+      it->second.mut.reset();
+      // freeze the subtree
+      it->second.state = EXPORT_FREEZING;
+      dir->auth_unpin(this);
+      ceph_assert(g_conf()->mds_kill_export_at != 3);
+
+    } else {
+      dout(7) << "peer failed to discover (not active?), canceling" << dendl;
+      export_try_cancel(dir, false);
+    }
+  }
+}
+
+class C_M_ExportSessionsFlushed : public MigratorContext {
+  CDir *dir;
+  uint64_t tid;
+public:
+  C_M_ExportSessionsFlushed(Migrator *m, CDir *d, uint64_t t) :
+    MigratorContext(m), dir(d), tid(t) {
+    dir->get(CDir::PIN_PTRWAITER);
+  }
+  void finish(int r) override {
+    mig->export_sessions_flushed(dir, tid);
+    dir->put(CDir::PIN_PTRWAITER);
+  }
+};
+
+void Migrator::export_sessions_flushed(CDir *dir, uint64_t tid)
+{
+  dout(7) << "export_sessions_flushed " << *dir << dendl;
+
+  map<CDir*,export_state_t>::iterator it = export_state.find(dir);
+  if (it == export_state.end() ||
+      it->second.state == EXPORT_CANCELLING ||
+      it->second.tid != tid) {
+    // export must have aborted.
+    dout(7) << "export must have aborted on " << dir << dendl;
+    return;
+  }
+
+  ceph_assert(it->second.state == EXPORT_PREPPING || it->second.state == EXPORT_WARNING);
+  ceph_assert(it->second.warning_ack_waiting.count(MDS_RANK_NONE) > 0);
+  it->second.warning_ack_waiting.erase(MDS_RANK_NONE);
+  if (it->second.state == EXPORT_WARNING && it->second.warning_ack_waiting.empty())
+    export_go(dir);     // start export.
+}
+
+void Migrator::export_frozen(CDir *dir, uint64_t tid)
+{
+  dout(7) << "export_frozen on " << *dir << dendl;
+
+  map<CDir*,export_state_t>::iterator it = export_state.find(dir);
+  if (it == export_state.end() || it->second.tid != tid) {
+    dout(7) << "export must have aborted" << dendl;
+    return;
+  }
+
+  ceph_assert(it->second.state == EXPORT_FREEZING);
+  ceph_assert(dir->is_frozen_tree_root());
+
+  CInode *diri = dir->get_inode();
+
+  // ok, try to grab all my locks.
+  MutationImpl::LockOpVec lov;
+  get_export_lock_set(dir, lov);
+  if ((diri->is_auth() && diri->is_frozen()) ||
+      !mds->locker->can_rdlock_set(lov) ||
+      !diri->filelock.can_wrlock(-1) ||
+      !diri->nestlock.can_wrlock(-1)) {
+    dout(7) << "export_dir couldn't acquire all needed locks, failing. "
+	    << *dir << dendl;
+    export_try_cancel(dir);
+    return;
+  }
+
+  it->second.mut = new MutationImpl();
+  if (diri->is_auth())
+    it->second.mut->auth_pin(diri);
+  mds->locker->rdlock_take_set(lov, it->second.mut);
+  mds->locker->wrlock_force(&diri->filelock, it->second.mut);
+  mds->locker->wrlock_force(&diri->nestlock, it->second.mut);
+
+  cache->show_subtrees();
+
+  // CDir::_freeze_tree() should have forced it into subtree.
+  ceph_assert(dir->get_dir_auth() == mds_authority_t(mds->get_nodeid(), mds->get_nodeid()));
+  // note the bounds.
+  set<CDir*> bounds;
+  cache->get_subtree_bounds(dir, bounds);
+
+  // generate prep message, log entry.
+  auto prep = MExportDirPrep::create(dir->dirfrag(), it->second.tid);
+
+  // include list of bystanders
+  for (const auto &p : dir->get_replicas()) {
+    if (p.first != it->second.peer) {
+      dout(10) << "bystander mds." << p.first << dendl;
+      prep->add_bystander(p.first);
+    }
+  }
+
+  // include base dirfrag
+  cache->replicate_dir(dir, it->second.peer, prep->basedir);
+  
+  /*
+   * include spanning tree for all nested exports.
+   * these need to be on the destination _before_ the final export so that
+   * dir_auth updates on any nested exports are properly absorbed.
+   * this includes inodes and dirfrags included in the subtree, but
+   * only the inodes at the bounds.
+   *
+   * each trace is: df ('-' | ('f' dir | 'd') dentry inode (dir dentry inode)*)
+   */
+  set<inodeno_t> inodes_added;
+  set<dirfrag_t> dirfrags_added;
+
+  // check bounds
+  for (set<CDir*>::iterator p = bounds.begin();
+       p != bounds.end();
+       ++p) {
+    CDir *bound = *p;
+
+    // pin it.
+    bound->get(CDir::PIN_EXPORTBOUND);
+    bound->state_set(CDir::STATE_EXPORTBOUND);
+    
+    dout(7) << "  export bound " << *bound << dendl;
+    prep->add_bound( bound->dirfrag() );
+
+    // trace to bound
+    bufferlist tracebl;
+    CDir *cur = bound;
+
+    char start = '-';
+    while (1) {
+      // don't repeat inodes
+      if (inodes_added.count(cur->inode->ino()))
+	break;
+      inodes_added.insert(cur->inode->ino());
+
+      // prepend dentry + inode
+      ceph_assert(cur->inode->is_auth());
+      bufferlist bl;
+      cache->replicate_dentry(cur->inode->parent, it->second.peer, bl);
+      dout(7) << "  added " << *cur->inode->parent << dendl;
+      cache->replicate_inode(cur->inode, it->second.peer, bl,
+			     mds->mdsmap->get_up_features());
+      dout(7) << "  added " << *cur->inode << dendl;
+      bl.claim_append(tracebl);
+      tracebl.claim(bl);
+
+      cur = cur->get_parent_dir();
+
+      // don't repeat dirfrags
+      if (dirfrags_added.count(cur->dirfrag()) ||
+	  cur == dir) {
+	start = 'd';  // start with dentry
+	break;
+      }
+      dirfrags_added.insert(cur->dirfrag());
+
+      // prepend dir
+      cache->replicate_dir(cur, it->second.peer, bl);
+      dout(7) << "  added " << *cur << dendl;
+      bl.claim_append(tracebl);
+      tracebl.claim(bl);
+
+      start = 'f';  // start with dirfrag
+    }
+    bufferlist final_bl;
+    dirfrag_t df = cur->dirfrag();
+    encode(df, final_bl);
+    encode(start, final_bl);
+    final_bl.claim_append(tracebl);
+    prep->add_trace(final_bl);
+  }
+
+  // send.
+  it->second.state = EXPORT_PREPPING;
+  mds->send_message_mds(prep, it->second.peer);
+  assert (g_conf()->mds_kill_export_at != 4);
+
+  // make sure any new instantiations of caps are flushed out
+  ceph_assert(it->second.warning_ack_waiting.empty());
+
+  set<client_t> export_client_set;
+  get_export_client_set(dir, export_client_set);
+
+  MDSGatherBuilder gather(g_ceph_context);
+  mds->server->flush_client_sessions(export_client_set, gather);
+  if (gather.has_subs()) {
+    it->second.warning_ack_waiting.insert(MDS_RANK_NONE);
+    gather.set_finisher(new C_M_ExportSessionsFlushed(this, dir, it->second.tid));
+    gather.activate();
+  }
+}
+
+void Migrator::get_export_client_set(CDir *dir, set<client_t>& client_set)
+{
+  deque<CDir*> dfs;
+  dfs.push_back(dir);
+  while (!dfs.empty()) {
+    CDir *dir = dfs.front();
+    dfs.pop_front();
+    for (auto& p : *dir) {
+      CDentry *dn = p.second;
+      if (!dn->get_linkage()->is_primary())
+	continue;
+      CInode *in = dn->get_linkage()->get_inode();
+      if (in->is_dir()) {
+	// directory?
+	vector<CDir*> ls;
+	in->get_dirfrags(ls);
+	for (auto& q : ls) {
+	  if (!q->state_test(CDir::STATE_EXPORTBOUND)) {
+	    // include nested dirfrag
+	    ceph_assert(q->get_dir_auth().first == CDIR_AUTH_PARENT);
+	    dfs.push_back(q); // it's ours, recurse (later)
+	  }
+	}
+      }
+      for (auto& q : in->get_client_caps()) {
+	client_set.insert(q.first);
+      }
+    }
+  }
+}
+
+void Migrator::get_export_client_set(CInode *in, set<client_t>& client_set)
+{
+  for (const auto &p : in->get_client_caps()) {
+    client_set.insert(p.first);
+  }
+}
+
+void Migrator::handle_export_prep_ack(const MExportDirPrepAck::const_ref &m)
+{
+  CDir *dir = cache->get_dirfrag(m->get_dirfrag());
+  mds_rank_t dest(m->get_source().num());
+  ceph_assert(dir);
+
+  dout(7) << "export_prep_ack " << *dir << dendl;
+
+  mds->hit_export_target(dest, -1);
+
+  map<CDir*,export_state_t>::iterator it = export_state.find(dir);
+  if (it == export_state.end() ||
+      it->second.tid != m->get_tid() ||
+      it->second.peer != mds_rank_t(m->get_source().num())) {
+    // export must have aborted.  
+    dout(7) << "export must have aborted" << dendl;
+    return;
+  }
+  ceph_assert(it->second.state == EXPORT_PREPPING);
+
+  if (!m->is_success()) {
+    dout(7) << "peer couldn't acquire all needed locks or wasn't active, canceling" << dendl;
+    export_try_cancel(dir, false);
+    return;
+  }
+
+  assert (g_conf()->mds_kill_export_at != 5);
+  // send warnings
+  set<CDir*> bounds;
+  cache->get_subtree_bounds(dir, bounds);
+
+  ceph_assert(it->second.warning_ack_waiting.empty() ||
+         (it->second.warning_ack_waiting.size() == 1 &&
+	  it->second.warning_ack_waiting.count(MDS_RANK_NONE) > 0));
+  ceph_assert(it->second.notify_ack_waiting.empty());
+
+  for (const auto &p : dir->get_replicas()) {
+    if (p.first == it->second.peer) continue;
+    if (mds->is_cluster_degraded() &&
+	!mds->mdsmap->is_clientreplay_or_active_or_stopping(p.first))
+      continue;  // only if active
+    it->second.warning_ack_waiting.insert(p.first);
+    it->second.notify_ack_waiting.insert(p.first);  // we'll eventually get a notifyack, too!
+
+    auto notify = MExportDirNotify::create(dir->dirfrag(), it->second.tid, true,
+        mds_authority_t(mds->get_nodeid(),CDIR_AUTH_UNKNOWN),
+        mds_authority_t(mds->get_nodeid(),it->second.peer));
+    for (auto &cdir : bounds) {
+      notify->get_bounds().push_back(cdir->dirfrag());
+    }
+    mds->send_message_mds(notify, p.first);
+    
+  }
+
+  it->second.state = EXPORT_WARNING;
+
+  ceph_assert(g_conf()->mds_kill_export_at != 6);
+  // nobody to warn?
+  if (it->second.warning_ack_waiting.empty())
+    export_go(dir);  // start export.
+}
+
+
+class C_M_ExportGo : public MigratorContext {
+  CDir *dir;
+  uint64_t tid;
+public:
+  C_M_ExportGo(Migrator *m, CDir *d, uint64_t t) :
+    MigratorContext(m), dir(d), tid(t) {
+    dir->get(CDir::PIN_PTRWAITER);
+  }
+  void finish(int r) override {
+    mig->export_go_synced(dir, tid);
+    dir->put(CDir::PIN_PTRWAITER);
+  }
+};
+
+void Migrator::export_go(CDir *dir)
+{
+  auto it = export_state.find(dir);
+  ceph_assert(it != export_state.end());
+  dout(7) << "export_go " << *dir << " to " << it->second.peer << dendl;
+
+  // first sync log to flush out e.g. any cap imports
+  mds->mdlog->wait_for_safe(new C_M_ExportGo(this, dir, it->second.tid));
+  mds->mdlog->flush();
+}
+
+void Migrator::export_go_synced(CDir *dir, uint64_t tid)
+{
+  map<CDir*,export_state_t>::iterator it = export_state.find(dir);
+  if (it == export_state.end() ||
+      it->second.state == EXPORT_CANCELLING ||
+      it->second.tid != tid) {
+    // export must have aborted.  
+    dout(7) << "export must have aborted on " << dir << dendl;
+    return;
+  }
+  ceph_assert(it->second.state == EXPORT_WARNING);
+  mds_rank_t dest = it->second.peer;
+
+  dout(7) << "export_go_synced " << *dir << " to " << dest << dendl;
+
+  cache->show_subtrees();
+  
+  it->second.state = EXPORT_EXPORTING;
+  ceph_assert(g_conf()->mds_kill_export_at != 7);
+
+  ceph_assert(dir->is_frozen_tree_root());
+
+  // set ambiguous auth
+  cache->adjust_subtree_auth(dir, mds->get_nodeid(), dest);
+
+  // take away the popularity we're sending.
+  mds->balancer->subtract_export(dir);
+  
+  // fill export message with cache data
+  auto req = MExportDir::create(dir->dirfrag(), it->second.tid);
+  map<client_t,entity_inst_t> exported_client_map;
+  map<client_t,client_metadata_t> exported_client_metadata_map;
+  uint64_t num_exported_inodes = encode_export_dir(req->export_data,
+					      dir,   // recur start point
+					      exported_client_map,
+					      exported_client_metadata_map);
+  encode(exported_client_map, req->client_map, mds->mdsmap->get_up_features());
+  encode(exported_client_metadata_map, req->client_map);
+
+  // add bounds to message
+  set<CDir*> bounds;
+  cache->get_subtree_bounds(dir, bounds);
+  for (set<CDir*>::iterator p = bounds.begin();
+       p != bounds.end();
+       ++p)
+    req->add_export((*p)->dirfrag());
+
+  // send
+  mds->send_message_mds(req, dest);
+  ceph_assert(g_conf()->mds_kill_export_at != 8);
+
+  mds->hit_export_target(dest, num_exported_inodes+1);
+
+  // stats
+  if (mds->logger) mds->logger->inc(l_mds_exported);
+  if (mds->logger) mds->logger->inc(l_mds_exported_inodes, num_exported_inodes);
+
+  cache->show_subtrees();
+}
+
+
+/** encode_export_inode
+ * update our local state for this inode to export.
+ * encode relevant state to be sent over the wire.
+ * used by: encode_export_dir, file_rename (if foreign)
+ *
+ * FIXME: the separation between CInode.encode_export and these methods 
+ * is pretty arbitrary and dumb.
+ */
+void Migrator::encode_export_inode(CInode *in, bufferlist& enc_state, 
+				   map<client_t,entity_inst_t>& exported_client_map,
+				   map<client_t,client_metadata_t>& exported_client_metadata_map)
+{
+  dout(7) << "encode_export_inode " << *in << dendl;
+  ceph_assert(!in->is_replica(mds->get_nodeid()));
+
+  encode(in->inode.ino, enc_state);
+  encode(in->last, enc_state);
+  in->encode_export(enc_state);
+
+  // caps 
+  encode_export_inode_caps(in, true, enc_state, exported_client_map, exported_client_metadata_map);
+}
+
+void Migrator::encode_export_inode_caps(CInode *in, bool auth_cap, bufferlist& bl,
+					map<client_t,entity_inst_t>& exported_client_map,
+					map<client_t,client_metadata_t>& exported_client_metadata_map)
+{
+  dout(20) << "encode_export_inode_caps " << *in << dendl;
+
+  // encode caps
+  map<client_t,Capability::Export> cap_map;
+  in->export_client_caps(cap_map);
+  encode(cap_map, bl);
+  if (auth_cap) {
+    encode(in->get_mds_caps_wanted(), bl);
+
+    in->state_set(CInode::STATE_EXPORTINGCAPS);
+    in->get(CInode::PIN_EXPORTINGCAPS);
+  }
+
+  // make note of clients named by exported capabilities
+  for (const auto &p : in->get_client_caps()) {
+    if (exported_client_map.count(p.first))
+      continue;
+    Session *session =  mds->sessionmap.get_session(entity_name_t::CLIENT(p.first.v));
+    exported_client_map[p.first] = session->info.inst;
+    exported_client_metadata_map[p.first] = session->info.client_metadata;
+  }
+}
+
+void Migrator::finish_export_inode_caps(CInode *in, mds_rank_t peer,
+					map<client_t,Capability::Import>& peer_imported)
+{
+  dout(20) << "finish_export_inode_caps " << *in << dendl;
+
+  in->state_clear(CInode::STATE_EXPORTINGCAPS);
+  in->put(CInode::PIN_EXPORTINGCAPS);
+
+  // tell (all) clients about migrating caps.. 
+  for (const auto &p : in->get_client_caps()) {
+    const Capability *cap = &p.second;
+    dout(7) << "finish_export_inode_caps telling client." << p.first
+	    << " exported caps on " << *in << dendl;
+    auto m = MClientCaps::create(CEPH_CAP_OP_EXPORT, in->ino(), 0,
+				     cap->get_cap_id(), cap->get_mseq(), mds->get_osd_epoch_barrier());
+
+    map<client_t,Capability::Import>::iterator q = peer_imported.find(p.first);
+    ceph_assert(q != peer_imported.end());
+    m->set_cap_peer(q->second.cap_id, q->second.issue_seq, q->second.mseq,
+		    (q->second.cap_id > 0 ? peer : -1), 0);
+    mds->send_message_client_counted(m, p.first);
+  }
+  in->clear_client_caps_after_export();
+  mds->locker->eval(in, CEPH_CAP_LOCKS);
+}
+
+void Migrator::finish_export_inode(CInode *in, mds_rank_t peer,
+				   map<client_t,Capability::Import>& peer_imported,
+				   MDSContext::vec& finished)
+{
+  dout(12) << "finish_export_inode " << *in << dendl;
+
+  // clean
+  if (in->is_dirty())
+    in->mark_clean();
+  
+  // clear/unpin cached_by (we're no longer the authority)
+  in->clear_replica_map();
+  
+  // twiddle lock states for auth -> replica transition
+  in->authlock.export_twiddle();
+  in->linklock.export_twiddle();
+  in->dirfragtreelock.export_twiddle();
+  in->filelock.export_twiddle();
+  in->nestlock.export_twiddle();
+  in->xattrlock.export_twiddle();
+  in->snaplock.export_twiddle();
+  in->flocklock.export_twiddle();
+  in->policylock.export_twiddle();
+  
+  // mark auth
+  ceph_assert(in->is_auth());
+  in->state_clear(CInode::STATE_AUTH);
+  in->replica_nonce = CInode::EXPORT_NONCE;
+  
+  in->clear_dirty_rstat();
+
+  // no more auth subtree? clear scatter dirty
+  if (!in->has_subtree_root_dirfrag(mds->get_nodeid()))
+    in->clear_scatter_dirty();
+
+  in->clear_dirty_parent();
+
+  in->clear_file_locks();
+
+  // waiters
+  in->take_waiting(CInode::WAIT_ANY_MASK, finished);
+
+  in->finish_export();
+  
+  finish_export_inode_caps(in, peer, peer_imported);
+}
+
+uint64_t Migrator::encode_export_dir(bufferlist& exportbl,
+				CDir *dir,
+				map<client_t,entity_inst_t>& exported_client_map,
+				map<client_t,client_metadata_t>& exported_client_metadata_map)
+{
+  uint64_t num_exported = 0;
+
+  dout(7) << "encode_export_dir " << *dir << " " << dir->get_num_head_items() << " head items" << dendl;
+  
+  ceph_assert(dir->get_projected_version() == dir->get_version());
+
+#ifdef MDS_VERIFY_FRAGSTAT
+  if (dir->is_complete())
+    dir->verify_fragstat();
+#endif
+
+  // dir 
+  dirfrag_t df = dir->dirfrag();
+  encode(df, exportbl);
+  dir->encode_export(exportbl);
+  
+  __u32 nden = dir->items.size();
+  encode(nden, exportbl);
+  
+  // dentries
+  list<CDir*> subdirs;
+  for (auto &p : *dir) {
+    CDentry *dn = p.second;
+    CInode *in = dn->get_linkage()->get_inode();
+
+    num_exported++;
+    
+    // -- dentry
+    dout(7) << "encode_export_dir exporting " << *dn << dendl;
+    
+    // dn name
+    encode(dn->get_name(), exportbl);
+    encode(dn->last, exportbl);
+    
+    // state
+    dn->encode_export(exportbl);
+    
+    // points to...
+    
+    // null dentry?
+    if (dn->get_linkage()->is_null()) {
+      exportbl.append("N", 1);  // null dentry
+      continue;
+    }
+    
+    if (dn->get_linkage()->is_remote()) {
+      // remote link
+      exportbl.append("L", 1);  // remote link
+      
+      inodeno_t ino = dn->get_linkage()->get_remote_ino();
+      unsigned char d_type = dn->get_linkage()->get_remote_d_type();
+      encode(ino, exportbl);
+      encode(d_type, exportbl);
+      continue;
+    }
+
+    // primary link
+    // -- inode
+    exportbl.append("I", 1);    // inode dentry
+    
+    encode_export_inode(in, exportbl, exported_client_map, exported_client_metadata_map);  // encode, and (update state for) export
+    
+    // directory?
+    list<CDir*> dfs;
+    in->get_dirfrags(dfs);
+    for (list<CDir*>::iterator p = dfs.begin(); p != dfs.end(); ++p) {
+      CDir *t = *p;
+      if (!t->state_test(CDir::STATE_EXPORTBOUND)) {
+	// include nested dirfrag
+	ceph_assert(t->get_dir_auth().first == CDIR_AUTH_PARENT);
+	subdirs.push_front(t);  // it's ours, recurse (later)
+      }
+    }
+  }
+
+  // subdirs
+  for (auto &dir : subdirs)
+    num_exported += encode_export_dir(exportbl, dir, exported_client_map, exported_client_metadata_map);
+
+  return num_exported;
+}
+
+void Migrator::finish_export_dir(CDir *dir, mds_rank_t peer,
+				 map<inodeno_t,map<client_t,Capability::Import> >& peer_imported,
+				 MDSContext::vec& finished, int *num_dentries)
+{
+  dout(10) << "finish_export_dir " << *dir << dendl;
+
+  // release open_by 
+  dir->clear_replica_map();
+
+  // mark
+  ceph_assert(dir->is_auth());
+  dir->state_clear(CDir::STATE_AUTH);
+  dir->remove_bloom();
+  dir->replica_nonce = CDir::EXPORT_NONCE;
+
+  if (dir->is_dirty())
+    dir->mark_clean();
+
+  // suck up all waiters
+  dir->take_waiting(CDir::WAIT_ANY_MASK, finished);    // all dir waiters
+  
+  // pop
+  dir->finish_export();
+
+  // dentries
+  list<CDir*> subdirs;
+  for (auto &p : *dir) {
+    CDentry *dn = p.second;
+    CInode *in = dn->get_linkage()->get_inode();
+
+    // dentry
+    dn->finish_export();
+
+    // inode?
+    if (dn->get_linkage()->is_primary()) {
+      finish_export_inode(in, peer, peer_imported[in->ino()], finished);
+
+      // subdirs?
+      in->get_nested_dirfrags(subdirs);
+    }
+
+    cache->touch_dentry_bottom(dn); // move dentry to tail of LRU
+    ++(*num_dentries);
+  }
+
+  // subdirs
+  for (list<CDir*>::iterator it = subdirs.begin(); it != subdirs.end(); ++it) 
+    finish_export_dir(*it, peer, peer_imported, finished, num_dentries);
+}
+
+class C_MDS_ExportFinishLogged : public MigratorLogContext {
+  CDir *dir;
+public:
+  C_MDS_ExportFinishLogged(Migrator *m, CDir *d) : MigratorLogContext(m), dir(d) {}
+  void finish(int r) override {
+    mig->export_logged_finish(dir);
+  }
+};
+
+
+/*
+ * i should get an export_ack from the export target.
+ */
+void Migrator::handle_export_ack(const MExportDirAck::const_ref &m)
+{
+  CDir *dir = cache->get_dirfrag(m->get_dirfrag());
+  mds_rank_t dest(m->get_source().num());
+  ceph_assert(dir);
+  ceph_assert(dir->is_frozen_tree_root());  // i'm exporting!
+
+  // yay!
+  dout(7) << "handle_export_ack " << *dir << dendl;
+
+  mds->hit_export_target(dest, -1);
+
+  map<CDir*,export_state_t>::iterator it = export_state.find(dir);
+  ceph_assert(it != export_state.end());
+  ceph_assert(it->second.state == EXPORT_EXPORTING);
+  ceph_assert(it->second.tid == m->get_tid());
+
+  auto bp = m->imported_caps.cbegin();
+  decode(it->second.peer_imported, bp);
+
+  it->second.state = EXPORT_LOGGINGFINISH;
+  assert (g_conf()->mds_kill_export_at != 9);
+  set<CDir*> bounds;
+  cache->get_subtree_bounds(dir, bounds);
+
+  // log completion. 
+  //  include export bounds, to ensure they're in the journal.
+  EExport *le = new EExport(mds->mdlog, dir, it->second.peer);;
+  mds->mdlog->start_entry(le);
+
+  le->metablob.add_dir_context(dir, EMetaBlob::TO_ROOT);
+  le->metablob.add_dir(dir, false);
+  for (set<CDir*>::iterator p = bounds.begin();
+       p != bounds.end();
+       ++p) {
+    CDir *bound = *p;
+    le->get_bounds().insert(bound->dirfrag());
+    le->metablob.add_dir_context(bound);
+    le->metablob.add_dir(bound, false);
+  }
+
+  // list us second, them first.
+  // this keeps authority().first in sync with subtree auth state in the journal.
+  cache->adjust_subtree_auth(dir, it->second.peer, mds->get_nodeid());
+
+  // log export completion, then finish (unfreeze, trigger finish context, etc.)
+  mds->mdlog->submit_entry(le, new C_MDS_ExportFinishLogged(this, dir));
+  mds->mdlog->flush();
+  assert (g_conf()->mds_kill_export_at != 10);
+}
+
+void Migrator::export_notify_abort(CDir *dir, export_state_t& stat, set<CDir*>& bounds)
+{
+  dout(7) << "export_notify_abort " << *dir << dendl;
+
+  ceph_assert(stat.state == EXPORT_CANCELLING);
+
+  if (stat.notify_ack_waiting.empty()) {
+    stat.state = EXPORT_CANCELLED;
+    return;
+  }
+
+  dir->auth_pin(this);
+
+  for (set<mds_rank_t>::iterator p = stat.notify_ack_waiting.begin();
+       p != stat.notify_ack_waiting.end();
+       ++p) {
+    auto notify = MExportDirNotify::create(dir->dirfrag(), stat.tid, true,
+        pair<int,int>(mds->get_nodeid(), stat.peer),
+        pair<int,int>(mds->get_nodeid(), CDIR_AUTH_UNKNOWN));
+    for (set<CDir*>::iterator i = bounds.begin(); i != bounds.end(); ++i)
+      notify->get_bounds().push_back((*i)->dirfrag());
+    mds->send_message_mds(notify, *p);
+  }
+}
+
+/*
+ * this happens if hte dest failes after i send teh export data but before it is acked
+ * that is, we don't know they safely received and logged it, so we reverse our changes
+ * and go on.
+ */
+void Migrator::export_reverse(CDir *dir, export_state_t& stat)
+{
+  dout(7) << "export_reverse " << *dir << dendl;
+
+  set<CInode*> to_eval;
+
+  set<CDir*> bounds;
+  cache->get_subtree_bounds(dir, bounds);
+
+  // remove exporting pins
+  list<CDir*> rq;
+  rq.push_back(dir);
+  while (!rq.empty()) {
+    CDir *t = rq.front(); 
+    rq.pop_front();
+    t->abort_export();
+    for (auto &p : *t) {
+      CDentry *dn = p.second;
+      dn->abort_export();
+      if (!dn->get_linkage()->is_primary())
+	continue;
+      CInode *in = dn->get_linkage()->get_inode();
+      in->abort_export();
+      if (in->state_test(CInode::STATE_EVALSTALECAPS)) {
+	in->state_clear(CInode::STATE_EVALSTALECAPS);
+	to_eval.insert(in);
+      }
+      if (in->is_dir())
+	in->get_nested_dirfrags(rq);
+    }
+  }
+  
+  // unpin bounds
+  for (auto bd : bounds) {
+    bd->put(CDir::PIN_EXPORTBOUND);
+    bd->state_clear(CDir::STATE_EXPORTBOUND);
+  }
+
+  // notify bystanders
+  export_notify_abort(dir, stat, bounds);
+
+  // unfreeze tree, with possible subtree merge.
+  cache->adjust_subtree_auth(dir, mds->get_nodeid(), mds->get_nodeid());
+
+  // process delayed expires
+  cache->process_delayed_expire(dir);
+
+  dir->unfreeze_tree();
+  cache->try_subtree_merge(dir);
+
+  // revoke/resume stale caps
+  for (auto in : to_eval) {
+    bool need_issue = false;
+    for (auto &p : in->client_caps) {
+      Capability *cap = &p.second;
+      if (!cap->is_stale()) {
+	need_issue = true;
+	break;
+      }
+    }
+    if (need_issue &&
+	(!in->is_auth() || !mds->locker->eval(in, CEPH_CAP_LOCKS)))
+      mds->locker->issue_caps(in);
+  }
+
+  cache->show_cache();
+}
+
+
+/*
+ * once i get the ack, and logged the EExportFinish(true),
+ * send notifies (if any), otherwise go straight to finish.
+ * 
+ */
+void Migrator::export_logged_finish(CDir *dir)
+{
+  dout(7) << "export_logged_finish " << *dir << dendl;
+
+  export_state_t& stat = export_state[dir];
+
+  // send notifies
+  set<CDir*> bounds;
+  cache->get_subtree_bounds(dir, bounds);
+
+  for (set<mds_rank_t>::iterator p = stat.notify_ack_waiting.begin();
+       p != stat.notify_ack_waiting.end();
+       ++p) {
+    auto notify = MExportDirNotify::create(dir->dirfrag(), stat.tid, true,
+        pair<int,int>(mds->get_nodeid(), stat.peer),
+        pair<int,int>(stat.peer, CDIR_AUTH_UNKNOWN));
+
+    for (set<CDir*>::iterator i = bounds.begin(); i != bounds.end(); ++i)
+      notify->get_bounds().push_back((*i)->dirfrag());
+    
+    mds->send_message_mds(notify, *p);
+  }
+
+  // wait for notifyacks
+  stat.state = EXPORT_NOTIFYING;
+  assert (g_conf()->mds_kill_export_at != 11);
+  
+  // no notifies to wait for?
+  if (stat.notify_ack_waiting.empty()) {
+    export_finish(dir);  // skip notify/notify_ack stage.
+  } else {
+    // notify peer to send cap import messages to clients
+    if (!mds->is_cluster_degraded() ||
+	mds->mdsmap->is_clientreplay_or_active_or_stopping(stat.peer)) {
+      mds->send_message_mds(MExportDirFinish::create(dir->dirfrag(), false, stat.tid), stat.peer);
+    } else {
+      dout(7) << "not sending MExportDirFinish, dest has failed" << dendl;
+    }
+  }
+}
+
+/*
+ * warning:
+ *  i'll get an ack from each bystander.
+ *  when i get them all, do the export.
+ * notify:
+ *  i'll get an ack from each bystander.
+ *  when i get them all, unfreeze and send the finish.
+ */
+void Migrator::handle_export_notify_ack(const MExportDirNotifyAck::const_ref &m)
+{
+  CDir *dir = cache->get_dirfrag(m->get_dirfrag());
+  mds_rank_t dest(m->get_source().num());
+  ceph_assert(dir);
+  mds_rank_t from = mds_rank_t(m->get_source().num());
+
+  mds->hit_export_target(dest, -1);
+
+  auto export_state_entry = export_state.find(dir);
+  if (export_state_entry != export_state.end()) {
+    export_state_t& stat = export_state_entry->second;
+    if (stat.state == EXPORT_WARNING &&
+	stat.warning_ack_waiting.erase(from)) {
+      // exporting. process warning.
+      dout(7) << "handle_export_notify_ack from " << m->get_source()
+	      << ": exporting, processing warning on " << *dir << dendl;
+      if (stat.warning_ack_waiting.empty())
+	export_go(dir);     // start export.
+    } else if (stat.state == EXPORT_NOTIFYING &&
+	       stat.notify_ack_waiting.erase(from)) {
+      // exporting. process notify.
+      dout(7) << "handle_export_notify_ack from " << m->get_source()
+	      << ": exporting, processing notify on " << *dir << dendl;
+      if (stat.notify_ack_waiting.empty())
+	export_finish(dir);
+    } else if (stat.state == EXPORT_CANCELLING &&
+	       m->get_new_auth().second == CDIR_AUTH_UNKNOWN && // not warning ack
+	       stat.notify_ack_waiting.erase(from)) {
+      dout(7) << "handle_export_notify_ack from " << m->get_source()
+	      << ": cancelling export, processing notify on " << *dir << dendl;
+      if (stat.notify_ack_waiting.empty()) {
+	export_cancel_finish(export_state_entry);
+      }
+    }
+  }
+  else {
+    auto import_state_entry = import_state.find(dir->dirfrag());
+    if (import_state_entry != import_state.end()) {
+      import_state_t& stat = import_state_entry->second;
+      if (stat.state == IMPORT_ABORTING) {
+	// reversing import
+	dout(7) << "handle_export_notify_ack from " << m->get_source()
+	  << ": aborting import on " << *dir << dendl;
+	ceph_assert(stat.bystanders.count(from));
+	stat.bystanders.erase(from);
+	if (stat.bystanders.empty())
+	  import_reverse_unfreeze(dir);
+      }
+    }
+  }
+}
+
+void Migrator::export_finish(CDir *dir)
+{
+  dout(5) << "export_finish " << *dir << dendl;
+
+  assert (g_conf()->mds_kill_export_at != 12);
+  map<CDir*,export_state_t>::iterator it = export_state.find(dir);
+  if (it == export_state.end()) {
+    dout(7) << "target must have failed, not sending final commit message.  export succeeded anyway." << dendl;
+    return;
+  }
+
+  // send finish/commit to new auth
+  if (!mds->is_cluster_degraded() ||
+      mds->mdsmap->is_clientreplay_or_active_or_stopping(it->second.peer)) {
+    mds->send_message_mds(MExportDirFinish::create(dir->dirfrag(), true, it->second.tid), it->second.peer);
+  } else {
+    dout(7) << "not sending MExportDirFinish last, dest has failed" << dendl;
+  }
+  ceph_assert(g_conf()->mds_kill_export_at != 13);
+  
+  // finish export (adjust local cache state)
+  int num_dentries = 0;
+  MDSContext::vec finished;
+  finish_export_dir(dir, it->second.peer,
+		    it->second.peer_imported, finished, &num_dentries);
+
+  ceph_assert(!dir->is_auth());
+  cache->adjust_subtree_auth(dir, it->second.peer);
+
+  // unpin bounds
+  set<CDir*> bounds;
+  cache->get_subtree_bounds(dir, bounds);
+  for (set<CDir*>::iterator p = bounds.begin();
+       p != bounds.end();
+       ++p) {
+    CDir *bd = *p;
+    bd->put(CDir::PIN_EXPORTBOUND);
+    bd->state_clear(CDir::STATE_EXPORTBOUND);
+  }
+
+  if (dir->state_test(CDir::STATE_AUXSUBTREE))
+    dir->state_clear(CDir::STATE_AUXSUBTREE);
+
+  // discard delayed expires
+  cache->discard_delayed_expire(dir);
+
+  dout(7) << "export_finish unfreezing" << dendl;
+
+  // unfreeze tree, with possible subtree merge.
+  //  (we do this _after_ removing EXPORTBOUND pins, to allow merges)
+  dir->unfreeze_tree();
+  cache->try_subtree_merge(dir);
+
+  // no more auth subtree? clear scatter dirty
+  if (!dir->get_inode()->is_auth() &&
+      !dir->get_inode()->has_subtree_root_dirfrag(mds->get_nodeid())) {
+    dir->get_inode()->clear_scatter_dirty();
+    // wake up scatter_nudge waiters
+    dir->get_inode()->take_waiting(CInode::WAIT_ANY_MASK, finished);
+  }
+
+  if (!finished.empty())
+    mds->queue_waiters(finished);
+
+  MutationRef mut = std::move(it->second.mut);
+  auto parent = std::move(it->second.parent);
+  // remove from exporting list, clean up state
+  total_exporting_size -= it->second.approx_size;
+  export_state.erase(it);
+
+  ceph_assert(dir->state_test(CDir::STATE_EXPORTING));
+  dir->clear_exporting();
+
+  cache->show_subtrees();
+  audit();
+
+  cache->trim(num_dentries); // try trimming exported dentries
+
+  // send pending import_maps?
+  mds->mdcache->maybe_send_pending_resolves();
+
+  // drop locks, unpin path
+  if (mut) {
+    mds->locker->drop_locks(mut.get());
+    mut->cleanup();
+  }
+
+  if (parent)
+    child_export_finish(parent, true);
+
+  maybe_do_queued_export();
+}
+
+
+
+class C_MDS_ExportDiscover : public MigratorContext {
+public:
+  C_MDS_ExportDiscover(Migrator *mig, const MExportDirDiscover::const_ref& m) : MigratorContext(mig), m(m) {}
+  void finish(int r) override {
+    mig->handle_export_discover(m, true);
+  }
+private:
+  MExportDirDiscover::const_ref m;
+};
+
+class C_MDS_ExportDiscoverFactory : public MDSContextFactory {
+public:
+  C_MDS_ExportDiscoverFactory(Migrator *mig, MExportDirDiscover::const_ref m) : mig(mig), m(m) {}
+  MDSContext *build() {
+    return new C_MDS_ExportDiscover(mig, m);
+  }
+private:
+  Migrator *mig;
+  MExportDirDiscover::const_ref m;
+};
+
+// ==========================================================
+// IMPORT
+
+void Migrator::handle_export_discover(const MExportDirDiscover::const_ref &m, bool started)
+{
+  mds_rank_t from = m->get_source_mds();
+  ceph_assert(from != mds->get_nodeid());
+
+  dout(7) << "handle_export_discover on " << m->get_path() << dendl;
+
+  // note import state
+  dirfrag_t df = m->get_dirfrag();
+
+  if (!mds->is_active()) {
+    dout(7) << " not active, send NACK " << dendl;
+    mds->send_message_mds(MExportDirDiscoverAck::create(df, m->get_tid(), false), from);
+    return;
+  }
+
+  // only start discovering on this message once.
+  import_state_t *p_state;
+  map<dirfrag_t,import_state_t>::iterator it = import_state.find(df);
+  if (!started) {
+    ceph_assert(it == import_state.end());
+    p_state = &import_state[df];
+    p_state->state = IMPORT_DISCOVERING;
+    p_state->peer = from;
+    p_state->tid = m->get_tid();
+  } else {
+    // am i retrying after ancient path_traverse results?
+    if (it == import_state.end() ||
+	it->second.peer != from ||
+	it->second.tid != m->get_tid()) {
+      dout(7) << " dropping obsolete message" << dendl;
+      return;
+    }
+    ceph_assert(it->second.state == IMPORT_DISCOVERING);
+    p_state = &it->second;
+  }
+
+  C_MDS_ExportDiscoverFactory cf(this, m);
+  if (!mds->mdcache->is_open()) {
+    dout(5) << " waiting for root" << dendl;
+    mds->mdcache->wait_for_open(cf.build());
+    return;
+  }
+
+  assert (g_conf()->mds_kill_import_at != 1);
+
+  // do we have it?
+  CInode *in = cache->get_inode(m->get_dirfrag().ino);
+  if (!in) {
+    // must discover it!
+    filepath fpath(m->get_path());
+    vector<CDentry*> trace;
+    MDRequestRef null_ref;
+    int r = cache->path_traverse(null_ref, cf, fpath, &trace, NULL, MDS_TRAVERSE_DISCOVER);
+    if (r > 0) return;
+    if (r < 0) {
+      dout(7) << "handle_export_discover failed to discover or not dir " << m->get_path() << ", NAK" << dendl;
+      ceph_abort();    // this shouldn't happen if the auth pins its path properly!!!!
+    }
+
+    ceph_abort(); // this shouldn't happen; the get_inode above would have succeeded.
+  }
+
+  // yay
+  dout(7) << "handle_export_discover have " << df << " inode " << *in << dendl;
+  
+  p_state->state = IMPORT_DISCOVERED;
+
+  // pin inode in the cache (for now)
+  ceph_assert(in->is_dir());
+  in->get(CInode::PIN_IMPORTING);
+
+  // reply
+  dout(7) << " sending export_discover_ack on " << *in << dendl;
+  mds->send_message_mds(MExportDirDiscoverAck::create(df, m->get_tid()), p_state->peer);
+  assert (g_conf()->mds_kill_import_at != 2);
+}
+
+void Migrator::import_reverse_discovering(dirfrag_t df)
+{
+  import_state.erase(df);
+}
+
+void Migrator::import_reverse_discovered(dirfrag_t df, CInode *diri)
+{
+  // unpin base
+  diri->put(CInode::PIN_IMPORTING);
+  import_state.erase(df);
+}
+
+void Migrator::import_reverse_prepping(CDir *dir, import_state_t& stat)
+{
+  set<CDir*> bounds;
+  cache->map_dirfrag_set(stat.bound_ls, bounds);
+  import_remove_pins(dir, bounds);
+  import_reverse_final(dir);
+}
+
+void Migrator::handle_export_cancel(const MExportDirCancel::const_ref &m)
+{
+  dout(7) << "handle_export_cancel on " << m->get_dirfrag() << dendl;
+  dirfrag_t df = m->get_dirfrag();
+  map<dirfrag_t,import_state_t>::iterator it = import_state.find(df);
+  if (it == import_state.end()) {
+    ceph_abort_msg("got export_cancel in weird state");
+  } else if (it->second.state == IMPORT_DISCOVERING) {
+    import_reverse_discovering(df);
+  } else if (it->second.state == IMPORT_DISCOVERED) {
+    CInode *in = cache->get_inode(df.ino);
+    ceph_assert(in);
+    import_reverse_discovered(df, in);
+  } else if (it->second.state == IMPORT_PREPPING) {
+    CDir *dir = mds->mdcache->get_dirfrag(df);
+    ceph_assert(dir);
+    import_reverse_prepping(dir, it->second);
+  } else if (it->second.state == IMPORT_PREPPED) {
+    CDir *dir = mds->mdcache->get_dirfrag(df);
+    ceph_assert(dir);
+    set<CDir*> bounds;
+    cache->get_subtree_bounds(dir, bounds);
+    import_remove_pins(dir, bounds);
+    // adjust auth back to the exportor
+    cache->adjust_subtree_auth(dir, it->second.peer);
+    import_reverse_unfreeze(dir);
+  } else {
+    ceph_abort_msg("got export_cancel in weird state");
+  }
+}
+
+class C_MDS_ExportPrep : public MigratorContext {
+public:
+  C_MDS_ExportPrep(Migrator *mig, const MExportDirPrep::const_ref& m) : MigratorContext(mig), m(m) {}
+  void finish(int r) override {
+    mig->handle_export_prep(m, true);
+  }
+private:
+  MExportDirPrep::const_ref m;
+};
+
+class C_MDS_ExportPrepFactory : public MDSContextFactory {
+public:
+  C_MDS_ExportPrepFactory(Migrator *mig, MExportDirPrep::const_ref m) : mig(mig), m(m) {}
+  MDSContext *build() {
+    return new C_MDS_ExportPrep(mig, m);
+  }
+private:
+  Migrator *mig;
+  MExportDirPrep::const_ref m;
+};
+
+void Migrator::handle_export_prep(const MExportDirPrep::const_ref &m, bool did_assim)
+{
+  mds_rank_t oldauth = mds_rank_t(m->get_source().num());
+  ceph_assert(oldauth != mds->get_nodeid());
+
+  CDir *dir;
+  CInode *diri;
+  MDSContext::vec finished;
+
+  // assimilate root dir.
+  map<dirfrag_t,import_state_t>::iterator it = import_state.find(m->get_dirfrag());
+  if (!did_assim) {
+    ceph_assert(it != import_state.end());
+    ceph_assert(it->second.state == IMPORT_DISCOVERED);
+    ceph_assert(it->second.peer == oldauth);
+    diri = cache->get_inode(m->get_dirfrag().ino);
+    ceph_assert(diri);
+    auto p = m->basedir.cbegin();
+    dir = cache->add_replica_dir(p, diri, oldauth, finished);
+    dout(7) << "handle_export_prep on " << *dir << " (first pass)" << dendl;
+  } else {
+    if (it == import_state.end() ||
+	it->second.peer != oldauth ||
+	it->second.tid != m->get_tid()) {
+      dout(7) << "handle_export_prep obsolete message, dropping" << dendl;
+      return;
+    }
+    ceph_assert(it->second.state == IMPORT_PREPPING);
+    ceph_assert(it->second.peer == oldauth);
+
+    dir = cache->get_dirfrag(m->get_dirfrag());
+    ceph_assert(dir);
+    dout(7) << "handle_export_prep on " << *dir << " (subsequent pass)" << dendl;
+    diri = dir->get_inode();
+  }
+  ceph_assert(dir->is_auth() == false);
+
+  cache->show_subtrees();
+
+  // build import bound map
+  map<inodeno_t, fragset_t> import_bound_fragset;
+  for (const auto &bound : m->get_bounds()) {
+    dout(10) << " bound " << bound << dendl;
+    import_bound_fragset[bound.ino].insert(bound.frag);
+  }
+
+  // assimilate contents?
+  if (!did_assim) {
+    dout(7) << "doing assim on " << *dir << dendl;
+
+    // change import state
+    it->second.state = IMPORT_PREPPING;
+    it->second.bound_ls = m->get_bounds();
+    it->second.bystanders = m->get_bystanders();
+    ceph_assert(g_conf()->mds_kill_import_at != 3);
+
+    // bystander list
+    dout(7) << "bystanders are " << it->second.bystanders << dendl;
+
+    // move pin to dir
+    diri->put(CInode::PIN_IMPORTING);
+    dir->get(CDir::PIN_IMPORTING);  
+    dir->state_set(CDir::STATE_IMPORTING);
+
+    // assimilate traces to exports
+    // each trace is: df ('-' | ('f' dir | 'd') dentry inode (dir dentry inode)*)
+    for (const auto &bl : m->traces) {
+      auto q = bl.cbegin();
+      dirfrag_t df;
+      decode(df, q);
+      char start;
+      decode(start, q);
+      dout(10) << " trace from " << df << " start " << start << " len " << bl.length() << dendl;
+
+      CDir *cur = 0;
+      if (start == 'd') {
+	cur = cache->get_dirfrag(df);
+	ceph_assert(cur);
+	dout(10) << "  had " << *cur << dendl;
+      } else if (start == 'f') {
+	CInode *in = cache->get_inode(df.ino);
+	ceph_assert(in);
+	dout(10) << "  had " << *in << dendl;
+	cur = cache->add_replica_dir(q, in, oldauth, finished);
+ 	dout(10) << "  added " << *cur << dendl;
+      } else if (start == '-') {
+	// nothing
+      } else
+	ceph_abort_msg("unrecognized start char");
+
+      while (!q.end()) {
+	CDentry *dn = cache->add_replica_dentry(q, cur, finished);
+	dout(10) << "  added " << *dn << dendl;
+	CInode *in = cache->add_replica_inode(q, dn, finished);
+	dout(10) << "  added " << *in << dendl;
+	if (q.end())
+	  break;
+	cur = cache->add_replica_dir(q, in, oldauth, finished);
+	dout(10) << "  added " << *cur << dendl;
+      }
+    }
+
+    // make bound sticky
+    for (map<inodeno_t,fragset_t>::iterator p = import_bound_fragset.begin();
+	 p != import_bound_fragset.end();
+	 ++p) {
+      CInode *in = cache->get_inode(p->first);
+      ceph_assert(in);
+      in->get_stickydirs();
+      dout(7) << " set stickydirs on bound inode " << *in << dendl;
+    }
+
+  } else {
+    dout(7) << " not doing assim on " << *dir << dendl;
+  }
+
+  MDSGatherBuilder gather(g_ceph_context);
+
+  if (!finished.empty())
+    mds->queue_waiters(finished);
+
+
+  bool success = true;
+  if (mds->is_active()) {
+    // open all bounds
+    set<CDir*> import_bounds;
+    for (map<inodeno_t,fragset_t>::iterator p = import_bound_fragset.begin();
+	 p != import_bound_fragset.end();
+	 ++p) {
+      CInode *in = cache->get_inode(p->first);
+      ceph_assert(in);
+
+      // map fragset into a frag_t list, based on the inode fragtree
+      frag_vec_t leaves;
+      for (const auto& frag : p->second) {
+	in->dirfragtree.get_leaves_under(frag, leaves);
+      }
+      dout(10) << " bound inode " << p->first << " fragset " << p->second << " maps to " << leaves << dendl;
+
+      for (const auto& leaf : leaves) {
+	CDir *bound = cache->get_dirfrag(dirfrag_t(p->first, leaf));
+	if (!bound) {
+	  dout(7) << "  opening bounding dirfrag " << leaf << " on " << *in << dendl;
+	  cache->open_remote_dirfrag(in, leaf, gather.new_sub());
+	  continue;
+	}
+
+	if (!bound->state_test(CDir::STATE_IMPORTBOUND)) {
+	  dout(7) << "  pinning import bound " << *bound << dendl;
+	  bound->get(CDir::PIN_IMPORTBOUND);
+	  bound->state_set(CDir::STATE_IMPORTBOUND);
+	} else {
+	  dout(7) << "  already pinned import bound " << *bound << dendl;
+	}
+	import_bounds.insert(bound);
+      }
+    }
+
+    if (gather.has_subs()) {
+      C_MDS_ExportPrepFactory cf(this, m);
+      gather.set_finisher(cf.build());
+      gather.activate();
+      return;
+    }
+
+    dout(7) << " all ready, noting auth and freezing import region" << dendl;
+
+    if (!mds->mdcache->is_readonly() &&
+	diri->filelock.can_wrlock(-1) &&
+	diri->nestlock.can_wrlock(-1)) {
+      it->second.mut = new MutationImpl();
+      // force some locks.  hacky.
+      mds->locker->wrlock_force(&dir->inode->filelock, it->second.mut);
+      mds->locker->wrlock_force(&dir->inode->nestlock, it->second.mut);
+
+      // note that i am an ambiguous auth for this subtree.
+      // specify bounds, since the exporter explicitly defines the region.
+      cache->adjust_bounded_subtree_auth(dir, import_bounds,
+					 pair<int,int>(oldauth, mds->get_nodeid()));
+      cache->verify_subtree_bounds(dir, import_bounds);
+      // freeze.
+      dir->_freeze_tree();
+      // note new state
+      it->second.state = IMPORT_PREPPED;
+    } else {
+      dout(7) << " couldn't acquire all needed locks, failing. " << *dir << dendl;
+      success = false;
+    }
+  } else {
+    dout(7) << " not active, failing. " << *dir << dendl;
+    success = false;
+  }
+
+  if (!success)
+    import_reverse_prepping(dir, it->second);
+
+  // ok!
+  dout(7) << " sending export_prep_ack on " << *dir << dendl;
+  mds->send_message(MExportDirPrepAck::create(dir->dirfrag(), success, m->get_tid()), m->get_connection());
+
+  ceph_assert(g_conf()->mds_kill_import_at != 4);
+}
+
+
+
+
+class C_MDS_ImportDirLoggedStart : public MigratorLogContext {
+  dirfrag_t df;
+  CDir *dir;
+  mds_rank_t from;
+public:
+  map<client_t,pair<Session*,uint64_t> > imported_session_map;
+
+  C_MDS_ImportDirLoggedStart(Migrator *m, CDir *d, mds_rank_t f) :
+    MigratorLogContext(m), df(d->dirfrag()), dir(d), from(f) {
+    dir->get(CDir::PIN_PTRWAITER);
+  }
+  void finish(int r) override {
+    mig->import_logged_start(df, dir, from, imported_session_map);
+    dir->put(CDir::PIN_PTRWAITER);
+  }
+};
+
+void Migrator::handle_export_dir(const MExportDir::const_ref &m)
+{
+  assert (g_conf()->mds_kill_import_at != 5);
+  CDir *dir = cache->get_dirfrag(m->dirfrag);
+  ceph_assert(dir);
+
+  mds_rank_t oldauth = mds_rank_t(m->get_source().num());
+  dout(7) << "handle_export_dir importing " << *dir << " from " << oldauth << dendl;
+
+  ceph_assert(!dir->is_auth());
+  ceph_assert(dir->freeze_tree_state);
+  
+  map<dirfrag_t,import_state_t>::iterator it = import_state.find(m->dirfrag);
+  ceph_assert(it != import_state.end());
+  ceph_assert(it->second.state == IMPORT_PREPPED);
+  ceph_assert(it->second.tid == m->get_tid());
+  ceph_assert(it->second.peer == oldauth);
+
+  if (!dir->get_inode()->dirfragtree.is_leaf(dir->get_frag()))
+    dir->get_inode()->dirfragtree.force_to_leaf(g_ceph_context, dir->get_frag());
+
+  cache->show_subtrees();
+
+  C_MDS_ImportDirLoggedStart *onlogged = new C_MDS_ImportDirLoggedStart(this, dir, oldauth);
+
+  // start the journal entry
+  EImportStart *le = new EImportStart(mds->mdlog, dir->dirfrag(), m->bounds, oldauth);
+  mds->mdlog->start_entry(le);
+
+  le->metablob.add_dir_context(dir);
+  
+  // adjust auth (list us _first_)
+  cache->adjust_subtree_auth(dir, mds->get_nodeid(), oldauth);
+
+  // new client sessions, open these after we journal
+  // include imported sessions in EImportStart
+  auto cmp = m->client_map.cbegin();
+  map<client_t,entity_inst_t> client_map;
+  map<client_t,client_metadata_t> client_metadata_map;
+  decode(client_map, cmp);
+  decode(client_metadata_map, cmp);
+  ceph_assert(cmp.end());
+  le->cmapv = mds->server->prepare_force_open_sessions(client_map, client_metadata_map,
+						       onlogged->imported_session_map);
+  encode(client_map, le->client_map, mds->mdsmap->get_up_features());
+  encode(client_metadata_map, le->client_map);
+
+  auto blp = m->export_data.cbegin();
+  int num_imported_inodes = 0;
+  while (!blp.end()) {
+    num_imported_inodes += 
+      decode_import_dir(blp,
+			oldauth, 
+			dir,                 // import root
+			le,
+			mds->mdlog->get_current_segment(),
+			it->second.peer_exports,
+			it->second.updated_scatterlocks);
+  }
+  dout(10) << " " << m->bounds.size() << " imported bounds" << dendl;
+  
+  // include bounds in EImportStart
+  set<CDir*> import_bounds;
+  for (const auto &bound : m->bounds) {
+    CDir *bd = cache->get_dirfrag(bound);
+    ceph_assert(bd);
+    le->metablob.add_dir(bd, false);  // note that parent metadata is already in the event
+    import_bounds.insert(bd);
+  }
+  cache->verify_subtree_bounds(dir, import_bounds);
+
+  // adjust popularity
+  mds->balancer->add_import(dir);
+
+  dout(7) << "handle_export_dir did " << *dir << dendl;
+
+  // note state
+  it->second.state = IMPORT_LOGGINGSTART;
+  assert (g_conf()->mds_kill_import_at != 6);
+
+  // log it
+  mds->mdlog->submit_entry(le, onlogged);
+  mds->mdlog->flush();
+
+  // some stats
+  if (mds->logger) {
+    mds->logger->inc(l_mds_imported);
+    mds->logger->inc(l_mds_imported_inodes, num_imported_inodes);
+  }
+}
+
+
+/*
+ * this is an import helper
+ *  called by import_finish, and import_reverse and friends.
+ */
+void Migrator::import_remove_pins(CDir *dir, set<CDir*>& bounds)
+{
+  import_state_t& stat = import_state[dir->dirfrag()];
+  // root
+  dir->put(CDir::PIN_IMPORTING);
+  dir->state_clear(CDir::STATE_IMPORTING);
+
+  // bounding inodes
+  set<inodeno_t> did;
+  for (list<dirfrag_t>::iterator p = stat.bound_ls.begin();
+       p != stat.bound_ls.end();
+       ++p) {
+    if (did.count(p->ino))
+      continue;
+    did.insert(p->ino);
+    CInode *in = cache->get_inode(p->ino);
+    ceph_assert(in);
+    in->put_stickydirs();
+  }
+
+  if (stat.state == IMPORT_PREPPING) {
+    for (auto bd : bounds) {
+      if (bd->state_test(CDir::STATE_IMPORTBOUND)) {
+	bd->put(CDir::PIN_IMPORTBOUND);
+	bd->state_clear(CDir::STATE_IMPORTBOUND);
+      }
+    }
+  } else if (stat.state >= IMPORT_PREPPED) {
+    // bounding dirfrags
+    for (auto bd : bounds) {
+      ceph_assert(bd->state_test(CDir::STATE_IMPORTBOUND));
+      bd->put(CDir::PIN_IMPORTBOUND);
+      bd->state_clear(CDir::STATE_IMPORTBOUND);
+    }
+  }
+}
+
+class C_MDC_QueueContexts : public MigratorContext {
+public:
+  MDSContext::vec contexts;
+  C_MDC_QueueContexts(Migrator *m) : MigratorContext(m) {}
+  void finish(int r) override {
+    // execute contexts immediately after 'this' context
+    get_mds()->queue_waiters_front(contexts);
+  }
+};
+
+/*
+ * note: this does teh full work of reversing and import and cleaning up
+ *  state.  
+ * called by both handle_mds_failure and by handle_resolve (if we are
+ *  a survivor coping with an exporter failure+recovery).
+ */
+void Migrator::import_reverse(CDir *dir)
+{
+  dout(7) << "import_reverse " << *dir << dendl;
+
+  import_state_t& stat = import_state[dir->dirfrag()];
+  stat.state = IMPORT_ABORTING;
+
+  set<CDir*> bounds;
+  cache->get_subtree_bounds(dir, bounds);
+
+  // remove pins
+  import_remove_pins(dir, bounds);
+
+  // update auth, with possible subtree merge.
+  ceph_assert(dir->is_subtree_root());
+  if (mds->is_resolve())
+    cache->trim_non_auth_subtree(dir);
+
+  cache->adjust_subtree_auth(dir, stat.peer);
+
+  auto fin = new C_MDC_QueueContexts(this);
+  if (!dir->get_inode()->is_auth() &&
+      !dir->get_inode()->has_subtree_root_dirfrag(mds->get_nodeid())) {
+    dir->get_inode()->clear_scatter_dirty();
+    // wake up scatter_nudge waiters
+    dir->get_inode()->take_waiting(CInode::WAIT_ANY_MASK, fin->contexts);
+  }
+
+  int num_dentries = 0;
+  // adjust auth bits.
+  list<CDir*> q;
+  q.push_back(dir);
+  while (!q.empty()) {
+    CDir *cur = q.front();
+    q.pop_front();
+    
+    // dir
+    cur->abort_import();
+
+    for (auto &p : *cur) {
+      CDentry *dn = p.second;
+
+      // dentry
+      dn->state_clear(CDentry::STATE_AUTH);
+      dn->clear_replica_map();
+      dn->set_replica_nonce(CDentry::EXPORT_NONCE);
+      if (dn->is_dirty()) 
+	dn->mark_clean();
+
+      // inode?
+      if (dn->get_linkage()->is_primary()) {
+	CInode *in = dn->get_linkage()->get_inode();
+	in->state_clear(CDentry::STATE_AUTH);
+	in->clear_replica_map();
+	in->set_replica_nonce(CInode::EXPORT_NONCE);
+	if (in->is_dirty()) 
+	  in->mark_clean();
+	in->clear_dirty_rstat();
+	if (!in->has_subtree_root_dirfrag(mds->get_nodeid())) {
+	  in->clear_scatter_dirty();
+	  in->take_waiting(CInode::WAIT_ANY_MASK, fin->contexts);
+	}
+
+	in->clear_dirty_parent();
+
+	in->authlock.clear_gather();
+	in->linklock.clear_gather();
+	in->dirfragtreelock.clear_gather();
+	in->filelock.clear_gather();
+
+	in->clear_file_locks();
+
+	// non-bounding dir?
+	list<CDir*> dfs;
+	in->get_dirfrags(dfs);
+	for (list<CDir*>::iterator p = dfs.begin(); p != dfs.end(); ++p)
+	  if (bounds.count(*p) == 0)
+	    q.push_back(*p);
+      }
+
+      cache->touch_dentry_bottom(dn); // move dentry to tail of LRU
+      ++num_dentries;
+    }
+  }
+
+  dir->add_waiter(CDir::WAIT_UNFREEZE, fin);
+
+  if (stat.state == IMPORT_ACKING) {
+    // remove imported caps
+    for (map<CInode*,map<client_t,Capability::Export> >::iterator p = stat.peer_exports.begin();
+	 p != stat.peer_exports.end();
+	 ++p) {
+      CInode *in = p->first;
+      for (map<client_t,Capability::Export>::iterator q = p->second.begin();
+	   q != p->second.end();
+	   ++q) {
+	Capability *cap = in->get_client_cap(q->first);
+	if (!cap) {
+	  ceph_assert(!stat.session_map.count(q->first));
+	  continue;
+	}
+	if (cap->is_importing())
+	  in->remove_client_cap(q->first);
+      }
+      in->put(CInode::PIN_IMPORTINGCAPS);
+    }
+    for (auto& p : stat.session_map) {
+      Session *session = p.second.first;
+      session->dec_importing();
+    }
+  }
+	 
+  // log our failure
+  mds->mdlog->start_submit_entry(new EImportFinish(dir, false));	// log failure
+
+  cache->trim(num_dentries); // try trimming dentries
+
+  // notify bystanders; wait in aborting state
+  import_notify_abort(dir, bounds);
+}
+
+void Migrator::import_notify_finish(CDir *dir, set<CDir*>& bounds)
+{
+  dout(7) << "import_notify_finish " << *dir << dendl;
+
+  import_state_t& stat = import_state[dir->dirfrag()];
+  for (set<mds_rank_t>::iterator p = stat.bystanders.begin();
+       p != stat.bystanders.end();
+       ++p) {
+    auto notify = MExportDirNotify::create(dir->dirfrag(), stat.tid, false,
+        pair<int,int>(stat.peer, mds->get_nodeid()),
+        pair<int,int>(mds->get_nodeid(), CDIR_AUTH_UNKNOWN));
+    for (set<CDir*>::iterator i = bounds.begin(); i != bounds.end(); ++i)
+      notify->get_bounds().push_back((*i)->dirfrag());
+    mds->send_message_mds(notify, *p);
+  }
+}
+
+void Migrator::import_notify_abort(CDir *dir, set<CDir*>& bounds)
+{
+  dout(7) << "import_notify_abort " << *dir << dendl;
+  
+  import_state_t& stat = import_state[dir->dirfrag()];
+  for (set<mds_rank_t>::iterator p = stat.bystanders.begin();
+       p != stat.bystanders.end(); ) {
+    if (mds->is_cluster_degraded() &&
+	!mds->mdsmap->is_clientreplay_or_active_or_stopping(*p)) {
+      // this can happen if both exporter and bystander fail in the same mdsmap epoch
+      stat.bystanders.erase(p++);
+      continue;
+    }
+    auto notify = MExportDirNotify::create(dir->dirfrag(), stat.tid, true,
+        mds_authority_t(stat.peer, mds->get_nodeid()),
+        mds_authority_t(stat.peer, CDIR_AUTH_UNKNOWN));
+    for (set<CDir*>::iterator i = bounds.begin(); i != bounds.end(); ++i)
+      notify->get_bounds().push_back((*i)->dirfrag());
+    mds->send_message_mds(notify, *p);
+    ++p;
+  }
+  if (stat.bystanders.empty()) {
+    dout(7) << "no bystanders, finishing reverse now" << dendl;
+    import_reverse_unfreeze(dir);
+  } else {
+    assert (g_conf()->mds_kill_import_at != 10);
+  }
+}
+
+void Migrator::import_reverse_unfreeze(CDir *dir)
+{
+  dout(7) << "import_reverse_unfreeze " << *dir << dendl;
+  ceph_assert(!dir->is_auth());
+  cache->discard_delayed_expire(dir);
+  dir->unfreeze_tree();
+  if (dir->is_subtree_root())
+    cache->try_subtree_merge(dir);
+  import_reverse_final(dir);
+}
+
+void Migrator::import_reverse_final(CDir *dir) 
+{
+  dout(7) << "import_reverse_final " << *dir << dendl;
+
+  // clean up
+  map<dirfrag_t, import_state_t>::iterator it = import_state.find(dir->dirfrag());
+  ceph_assert(it != import_state.end());
+
+  MutationRef mut = it->second.mut;
+  import_state.erase(it);
+
+  // send pending import_maps?
+  mds->mdcache->maybe_send_pending_resolves();
+
+  if (mut) {
+    mds->locker->drop_locks(mut.get());
+    mut->cleanup();
+  }
+
+  cache->show_subtrees();
+  //audit();  // this fails, bc we munge up the subtree map during handle_import_map (resolve phase)
+}
+
+
+
+
+void Migrator::import_logged_start(dirfrag_t df, CDir *dir, mds_rank_t from,
+				   map<client_t,pair<Session*,uint64_t> >& imported_session_map)
+{
+  dout(7) << "import_logged " << *dir << dendl;
+
+  map<dirfrag_t, import_state_t>::iterator it = import_state.find(dir->dirfrag());
+  if (it == import_state.end() ||
+      it->second.state != IMPORT_LOGGINGSTART) {
+    dout(7) << "import " << df << " must have aborted" << dendl;
+    mds->server->finish_force_open_sessions(imported_session_map);
+    return;
+  }
+
+  // note state
+  it->second.state = IMPORT_ACKING;
+
+  assert (g_conf()->mds_kill_import_at != 7);
+
+  // force open client sessions and finish cap import
+  mds->server->finish_force_open_sessions(imported_session_map, false);
+  
+  map<inodeno_t,map<client_t,Capability::Import> > imported_caps;
+  for (map<CInode*, map<client_t,Capability::Export> >::iterator p = it->second.peer_exports.begin();
+       p != it->second.peer_exports.end();
+       ++p) {
+    // parameter 'peer' is NONE, delay sending cap import messages to client
+    finish_import_inode_caps(p->first, MDS_RANK_NONE, true, imported_session_map,
+			     p->second, imported_caps[p->first->ino()]);
+  }
+
+  it->second.session_map.swap(imported_session_map);
+  
+  // send notify's etc.
+  dout(7) << "sending ack for " << *dir << " to old auth mds." << from << dendl;
+
+  // test surviving observer of a failed migration that did not complete
+  //assert(dir->replica_map.size() < 2 || mds->get_nodeid() != 0);
+
+  auto ack = MExportDirAck::create(dir->dirfrag(), it->second.tid);
+  encode(imported_caps, ack->imported_caps);
+
+  mds->send_message_mds(ack, from);
+  assert (g_conf()->mds_kill_import_at != 8);
+
+  cache->show_subtrees();
+}
+
+void Migrator::handle_export_finish(const MExportDirFinish::const_ref &m)
+{
+  CDir *dir = cache->get_dirfrag(m->get_dirfrag());
+  ceph_assert(dir);
+  dout(7) << "handle_export_finish on " << *dir << (m->is_last() ? " last" : "") << dendl;
+
+  map<dirfrag_t,import_state_t>::iterator it = import_state.find(m->get_dirfrag());
+  ceph_assert(it != import_state.end());
+  ceph_assert(it->second.tid == m->get_tid());
+
+  import_finish(dir, false, m->is_last());
+}
+
+void Migrator::import_finish(CDir *dir, bool notify, bool last)
+{
+  dout(7) << "import_finish on " << *dir << dendl;
+
+  map<dirfrag_t,import_state_t>::iterator it = import_state.find(dir->dirfrag());
+  ceph_assert(it != import_state.end());
+  ceph_assert(it->second.state == IMPORT_ACKING || it->second.state == IMPORT_FINISHING);
+
+  if (it->second.state == IMPORT_ACKING) {
+    ceph_assert(dir->is_auth());
+    cache->adjust_subtree_auth(dir, mds->get_nodeid(), mds->get_nodeid());
+  }
+
+  // log finish
+  ceph_assert(g_conf()->mds_kill_import_at != 9);
+
+  if (it->second.state == IMPORT_ACKING) {
+    for (map<CInode*, map<client_t,Capability::Export> >::iterator p = it->second.peer_exports.begin();
+	p != it->second.peer_exports.end();
+	++p) {
+      CInode *in = p->first;
+      ceph_assert(in->is_auth());
+      for (map<client_t,Capability::Export>::iterator q = p->second.begin();
+	  q != p->second.end();
+	  ++q) {
+	auto r = it->second.session_map.find(q->first);
+	if (r == it->second.session_map.end())
+	  continue;
+
+	Session *session = r->second.first;
+	Capability *cap = in->get_client_cap(q->first);
+	ceph_assert(cap);
+	cap->merge(q->second, true);
+	cap->clear_importing();
+	mds->mdcache->do_cap_import(session, in, cap, q->second.cap_id, q->second.seq,
+				    q->second.mseq - 1, it->second.peer, CEPH_CAP_FLAG_AUTH);
+      }
+      p->second.clear();
+      in->replica_caps_wanted = 0;
+    }
+    for (auto& p : it->second.session_map) {
+      Session *session = p.second.first;
+      session->dec_importing();
+    }
+  }
+
+  if (!last) {
+    ceph_assert(it->second.state == IMPORT_ACKING);
+    it->second.state = IMPORT_FINISHING;
+    return;
+  }
+
+  // remove pins
+  set<CDir*> bounds;
+  cache->get_subtree_bounds(dir, bounds);
+
+  if (notify)
+    import_notify_finish(dir, bounds);
+
+  import_remove_pins(dir, bounds);
+
+  map<CInode*, map<client_t,Capability::Export> > peer_exports;
+  it->second.peer_exports.swap(peer_exports);
+
+  // clear import state (we're done!)
+  MutationRef mut = it->second.mut;
+  import_state.erase(it);
+
+  mds->mdlog->start_submit_entry(new EImportFinish(dir, true));
+
+  // process delayed expires
+  cache->process_delayed_expire(dir);
+
+  // unfreeze tree, with possible subtree merge.
+  dir->unfreeze_tree();
+  cache->try_subtree_merge(dir);
+
+  cache->show_subtrees();
+  //audit();  // this fails, bc we munge up the subtree map during handle_import_map (resolve phase)
+
+  if (mut) {
+    mds->locker->drop_locks(mut.get());
+    mut->cleanup();
+  }
+
+  // re-eval imported caps
+  for (map<CInode*, map<client_t,Capability::Export> >::iterator p = peer_exports.begin();
+       p != peer_exports.end();
+       ++p) {
+    if (p->first->is_auth())
+      mds->locker->eval(p->first, CEPH_CAP_LOCKS, true);
+    p->first->put(CInode::PIN_IMPORTINGCAPS);
+  }
+
+  // send pending import_maps?
+  mds->mdcache->maybe_send_pending_resolves();
+
+  // did i just import mydir?
+  if (dir->ino() == MDS_INO_MDSDIR(mds->get_nodeid()))
+    cache->populate_mydir();
+
+  // is it empty?
+  if (dir->get_num_head_items() == 0 &&
+      !dir->inode->is_auth()) {
+    // reexport!
+    export_empty_import(dir);
+  }
+}
+
+
+void Migrator::decode_import_inode(CDentry *dn, bufferlist::const_iterator& blp,
+				   mds_rank_t oldauth, LogSegment *ls,
+				   map<CInode*, map<client_t,Capability::Export> >& peer_exports,
+				   list<ScatterLock*>& updated_scatterlocks)
+{  
+  dout(15) << "decode_import_inode on " << *dn << dendl;
+
+  inodeno_t ino;
+  snapid_t last;
+  decode(ino, blp);
+  decode(last, blp);
+
+  bool added = false;
+  CInode *in = cache->get_inode(ino, last);
+  if (!in) {
+    in = new CInode(mds->mdcache, true, 1, last);
+    added = true;
+  }
+
+  // state after link  -- or not!  -sage
+  in->decode_import(blp, ls);  // cap imports are noted for later action
+
+  // caps
+  decode_import_inode_caps(in, true, blp, peer_exports);
+
+  // link before state  -- or not!  -sage
+  if (dn->get_linkage()->get_inode() != in) {
+    ceph_assert(!dn->get_linkage()->get_inode());
+    dn->dir->link_primary_inode(dn, in);
+  }
+
+  if (in->is_dir())
+    dn->dir->pop_lru_subdirs.push_back(&in->item_pop_lru);
+ 
+  // add inode?
+  if (added) {
+    cache->add_inode(in);
+    dout(10) << "added " << *in << dendl;
+  } else {
+    dout(10) << "  had " << *in << dendl;
+  }
+
+  if (in->inode.is_dirty_rstat())
+    in->mark_dirty_rstat();
+  
+  // clear if dirtyscattered, since we're going to journal this
+  //  but not until we _actually_ finish the import...
+  if (in->filelock.is_dirty()) {
+    updated_scatterlocks.push_back(&in->filelock);
+    mds->locker->mark_updated_scatterlock(&in->filelock);
+  }
+
+  if (in->dirfragtreelock.is_dirty()) {
+    updated_scatterlocks.push_back(&in->dirfragtreelock);
+    mds->locker->mark_updated_scatterlock(&in->dirfragtreelock);
+  }
+
+  // adjust replica list
+  //assert(!in->is_replica(oldauth));  // not true on failed export
+  in->add_replica(oldauth, CInode::EXPORT_NONCE);
+  if (in->is_replica(mds->get_nodeid()))
+    in->remove_replica(mds->get_nodeid());
+
+  if (in->snaplock.is_stable() &&
+      in->snaplock.get_state() != LOCK_SYNC)
+      mds->locker->try_eval(&in->snaplock, NULL);
+}
+
+void Migrator::decode_import_inode_caps(CInode *in, bool auth_cap,
+					bufferlist::const_iterator &blp,
+					map<CInode*, map<client_t,Capability::Export> >& peer_exports)
+{
+  map<client_t,Capability::Export> cap_map;
+  decode(cap_map, blp);
+  if (auth_cap) {
+    mempool::mds_co::compact_map<int32_t,int32_t> mds_wanted;
+    decode(mds_wanted, blp);
+    mds_wanted.erase(mds->get_nodeid());
+    in->set_mds_caps_wanted(mds_wanted);
+  }
+  if (!cap_map.empty() ||
+      (auth_cap && (in->get_caps_wanted() & ~CEPH_CAP_PIN))) {
+    peer_exports[in].swap(cap_map);
+    in->get(CInode::PIN_IMPORTINGCAPS);
+  }
+}
+
+void Migrator::finish_import_inode_caps(CInode *in, mds_rank_t peer, bool auth_cap,
+					const map<client_t,pair<Session*,uint64_t> >& session_map,
+					const map<client_t,Capability::Export> &export_map,
+					map<client_t,Capability::Import> &import_map)
+{
+  for (auto& it : export_map) {
+    dout(10) << "finish_import_inode_caps for client." << it.first << " on " << *in << dendl;
+
+    auto p = session_map.find(it.first);
+    if (p == session_map.end()) {
+      dout(10) << " no session for client." << it.first << dendl;
+      (void)import_map[it.first];
+      continue;
+    }
+
+    Session *session = p->second.first;
+
+    Capability *cap = in->get_client_cap(it.first);
+    if (!cap) {
+      cap = in->add_client_cap(it.first, session);
+      if (peer < 0)
+	cap->mark_importing();
+    }
+
+    // Always ask exporter mds to send cap export messages for auth caps.
+    // For non-auth caps, ask exporter mds to send cap export messages to
+    // clients who haven't opened sessions. The cap export messages will
+    // make clients open sessions.
+    if (auth_cap || !session->get_connection()) {
+      Capability::Import& im = import_map[it.first];
+      im.cap_id = cap->get_cap_id();
+      im.mseq = auth_cap ? it.second.mseq : cap->get_mseq();
+      im.issue_seq = cap->get_last_seq() + 1;
+    }
+
+    if (peer >= 0) {
+      cap->merge(it.second, auth_cap);
+      mds->mdcache->do_cap_import(session, in, cap, it.second.cap_id,
+				  it.second.seq, it.second.mseq - 1, peer,
+				  auth_cap ? CEPH_CAP_FLAG_AUTH : CEPH_CAP_FLAG_RELEASE);
+    }
+  }
+
+  if (peer >= 0) {
+    in->replica_caps_wanted = 0;
+    in->put(CInode::PIN_IMPORTINGCAPS);
+  }
+}
+
+int Migrator::decode_import_dir(bufferlist::const_iterator& blp,
+				mds_rank_t oldauth,
+				CDir *import_root,
+				EImportStart *le,
+				LogSegment *ls,
+				map<CInode*,map<client_t,Capability::Export> >& peer_exports,
+				list<ScatterLock*>& updated_scatterlocks)
+{
+  // set up dir
+  dirfrag_t df;
+  decode(df, blp);
+
+  CInode *diri = cache->get_inode(df.ino);
+  ceph_assert(diri);
+  CDir *dir = diri->get_or_open_dirfrag(mds->mdcache, df.frag);
+  ceph_assert(dir);
+  
+  dout(7) << "decode_import_dir " << *dir << dendl;
+
+  if (!dir->freeze_tree_state) {
+    ceph_assert(dir->get_version() == 0);
+    dir->freeze_tree_state = import_root->freeze_tree_state;
+  }
+
+  // assimilate state
+  dir->decode_import(blp, ls);
+
+  // adjust replica list
+  //assert(!dir->is_replica(oldauth));    // not true on failed export
+  dir->add_replica(oldauth, CDir::EXPORT_NONCE);
+  if (dir->is_replica(mds->get_nodeid()))
+    dir->remove_replica(mds->get_nodeid());
+
+  // add to journal entry
+  if (le) 
+    le->metablob.add_import_dir(dir);
+
+  int num_imported = 0;
+
+  // take all waiters on this dir
+  // NOTE: a pass of imported data is guaranteed to get all of my waiters because
+  // a replica's presense in my cache implies/forces it's presense in authority's.
+  MDSContext::vec waiters;
+  dir->take_waiting(CDir::WAIT_ANY_MASK, waiters);
+  for (auto c : waiters)
+    dir->add_waiter(CDir::WAIT_UNFREEZE, c);  // UNFREEZE will get kicked both on success or failure
+  
+  dout(15) << "doing contents" << dendl;
+  
+  // contents
+  __u32 nden;
+  decode(nden, blp);
+  
+  for (; nden>0; nden--) {
+    num_imported++;
+    
+    // dentry
+    string dname;
+    snapid_t last;
+    decode(dname, blp);
+    decode(last, blp);
+    
+    CDentry *dn = dir->lookup_exact_snap(dname, last);
+    if (!dn)
+      dn = dir->add_null_dentry(dname, 1, last);
+    
+    dn->decode_import(blp, ls);
+
+    dn->add_replica(oldauth, CDentry::EXPORT_NONCE);
+    if (dn->is_replica(mds->get_nodeid()))
+      dn->remove_replica(mds->get_nodeid());
+
+    // dentry lock in unreadable state can block path traverse
+    if (dn->lock.get_state() != LOCK_SYNC)
+      mds->locker->try_eval(&dn->lock, NULL);
+
+    dout(15) << "decode_import_dir got " << *dn << dendl;
+    
+    // points to...
+    char icode;
+    decode(icode, blp);
+    
+    if (icode == 'N') {
+      // null dentry
+      ceph_assert(dn->get_linkage()->is_null());  
+      
+      // fall thru
+    }
+    else if (icode == 'L') {
+      // remote link
+      inodeno_t ino;
+      unsigned char d_type;
+      decode(ino, blp);
+      decode(d_type, blp);
+      if (dn->get_linkage()->is_remote()) {
+	ceph_assert(dn->get_linkage()->get_remote_ino() == ino);
+      } else {
+	dir->link_remote_inode(dn, ino, d_type);
+      }
+    }
+    else if (icode == 'I') {
+      // inode
+      ceph_assert(le);
+      decode_import_inode(dn, blp, oldauth, ls,
+			  peer_exports, updated_scatterlocks);
+    }
+    
+    // add dentry to journal entry
+    if (le)
+      le->metablob.add_import_dentry(dn);
+  }
+  
+#ifdef MDS_VERIFY_FRAGSTAT
+  if (dir->is_complete())
+    dir->verify_fragstat();
+#endif
+
+  dir->inode->maybe_export_pin();
+
+  dout(7) << "decode_import_dir done " << *dir << dendl;
+  return num_imported;
+}
+
+
+
+
+
+// authority bystander
+
+void Migrator::handle_export_notify(const MExportDirNotify::const_ref &m)
+{
+  if (!(mds->is_clientreplay() || mds->is_active() || mds->is_stopping())) {
+    return;
+  }
+
+  CDir *dir = cache->get_dirfrag(m->get_dirfrag());
+
+  mds_rank_t from = mds_rank_t(m->get_source().num());
+  mds_authority_t old_auth = m->get_old_auth();
+  mds_authority_t new_auth = m->get_new_auth();
+  
+  if (!dir) {
+    dout(7) << "handle_export_notify " << old_auth << " -> " << new_auth
+	    << " on missing dir " << m->get_dirfrag() << dendl;
+  } else if (dir->authority() != old_auth) {
+    dout(7) << "handle_export_notify old_auth was " << dir->authority() 
+	    << " != " << old_auth << " -> " << new_auth
+	    << " on " << *dir << dendl;
+  } else {
+    dout(7) << "handle_export_notify " << old_auth << " -> " << new_auth
+	    << " on " << *dir << dendl;
+    // adjust auth
+    set<CDir*> have;
+    cache->map_dirfrag_set(m->get_bounds(), have);
+    cache->adjust_bounded_subtree_auth(dir, have, new_auth);
+    
+    // induce a merge?
+    cache->try_subtree_merge(dir);
+  }
+  
+  // send ack
+  if (m->wants_ack()) {
+    mds->send_message_mds(MExportDirNotifyAck::create(m->get_dirfrag(), m->get_tid(), m->get_new_auth()), from);
+  } else {
+    // aborted.  no ack.
+    dout(7) << "handle_export_notify no ack requested" << dendl;
+  }
+}
+
+/** cap exports **/
+void Migrator::export_caps(CInode *in)
+{
+  mds_rank_t dest = in->authority().first;
+  dout(7) << "export_caps to mds." << dest << " " << *in << dendl;
+
+  ceph_assert(in->is_any_caps());
+  ceph_assert(!in->is_auth());
+  ceph_assert(!in->is_ambiguous_auth());
+  ceph_assert(!in->state_test(CInode::STATE_EXPORTINGCAPS));
+
+  auto ex = MExportCaps::create();
+  ex->ino = in->ino();
+
+  encode_export_inode_caps(in, false, ex->cap_bl, ex->client_map, ex->client_metadata_map);
+
+  mds->send_message_mds(ex, dest);
+}
+
+void Migrator::handle_export_caps_ack(const MExportCapsAck::const_ref &ack)
+{
+  mds_rank_t from = ack->get_source().num();
+  CInode *in = cache->get_inode(ack->ino);
+  if (in) {
+    ceph_assert(!in->is_auth());
+
+    dout(10) << "handle_export_caps_ack " << *ack << " from "
+	     << ack->get_source() << " on " << *in << dendl;
+
+    map<client_t,Capability::Import> imported_caps;
+    map<client_t,uint64_t> caps_ids;
+    auto blp = ack->cap_bl.cbegin();
+    decode(imported_caps, blp);
+    decode(caps_ids, blp);
+
+    for (auto& it : imported_caps) {
+      Capability *cap = in->get_client_cap(it.first);
+      if (!cap || cap->get_cap_id() != caps_ids.at(it.first))
+	continue;
+
+      dout(7) << __func__ << " telling client." << it.first
+	      << " exported caps on " << *in << dendl;
+      auto m = MClientCaps::create(CEPH_CAP_OP_EXPORT, in->ino(), 0,
+				       cap->get_cap_id(), cap->get_mseq(),
+				       mds->get_osd_epoch_barrier());
+      m->set_cap_peer(it.second.cap_id, it.second.issue_seq, it.second.mseq, from, 0);
+      mds->send_message_client_counted(m, it.first);
+
+      in->remove_client_cap(it.first);
+    }
+
+    mds->locker->request_inode_file_caps(in);
+    mds->locker->try_eval(in, CEPH_CAP_LOCKS);
+  }
+}
+
+void Migrator::handle_gather_caps(const MGatherCaps::const_ref &m)
+{
+  CInode *in = cache->get_inode(m->ino);
+  if (!in)
+    return;
+
+  dout(10) << "handle_gather_caps " << *m << " from " << m->get_source()
+           << " on " << *in << dendl;
+
+  if (in->is_any_caps() &&
+      !in->is_auth() &&
+      !in->is_ambiguous_auth() &&
+      !in->state_test(CInode::STATE_EXPORTINGCAPS))
+    export_caps(in);
+}
+
+class C_M_LoggedImportCaps : public MigratorLogContext {
+  CInode *in;
+  mds_rank_t from;
+public:
+  map<client_t,pair<Session*,uint64_t> > imported_session_map;
+  map<CInode*, map<client_t,Capability::Export> > peer_exports;
+
+  C_M_LoggedImportCaps(Migrator *m, CInode *i, mds_rank_t f) : MigratorLogContext(m), in(i), from(f) {}
+  void finish(int r) override {
+    mig->logged_import_caps(in, from, imported_session_map, peer_exports);
+  }  
+};
+
+void Migrator::handle_export_caps(const MExportCaps::const_ref &ex)
+{
+  dout(10) << "handle_export_caps " << *ex << " from " << ex->get_source() << dendl;
+  CInode *in = cache->get_inode(ex->ino);
+  
+  ceph_assert(in);
+  ceph_assert(in->is_auth());
+
+  // FIXME
+  if (!in->can_auth_pin()) {
+    return;
+  }
+
+  in->auth_pin(this);
+
+  map<client_t,entity_inst_t> client_map{ex->client_map};
+  map<client_t,client_metadata_t> client_metadata_map{ex->client_metadata_map};
+
+  C_M_LoggedImportCaps *finish = new C_M_LoggedImportCaps(
+      this, in, mds_rank_t(ex->get_source().num()));
+
+  version_t pv = mds->server->prepare_force_open_sessions(client_map, client_metadata_map,
+							  finish->imported_session_map);
+  // decode new caps
+  auto blp = ex->cap_bl.cbegin();
+  decode_import_inode_caps(in, false, blp, finish->peer_exports);
+  ceph_assert(!finish->peer_exports.empty());   // thus, inode is pinned.
+
+  // journal open client sessions
+  ESessions *le = new ESessions(pv, std::move(client_map),
+				std::move(client_metadata_map));
+  mds->mdlog->start_submit_entry(le, finish);
+  mds->mdlog->flush();
+}
+
+
+void Migrator::logged_import_caps(CInode *in, 
+				  mds_rank_t from,
+				  map<client_t,pair<Session*,uint64_t> >& imported_session_map,
+				  map<CInode*, map<client_t,Capability::Export> >& peer_exports)
+{
+  dout(10) << "logged_import_caps on " << *in << dendl;
+  // see export_go() vs export_go_synced()
+  ceph_assert(in->is_auth());
+
+  // force open client sessions and finish cap import
+  mds->server->finish_force_open_sessions(imported_session_map);
+
+  auto it = peer_exports.find(in);
+  ceph_assert(it != peer_exports.end());
+
+  // clients will release caps from the exporter when they receive the cap import message.
+  map<client_t,Capability::Import> imported_caps;
+  finish_import_inode_caps(in, from, false, imported_session_map, it->second, imported_caps);
+  mds->locker->eval(in, CEPH_CAP_LOCKS, true);
+
+  if (!imported_caps.empty()) {
+    auto ack = MExportCapsAck::create(in->ino());
+    map<client_t,uint64_t> peer_caps_ids;
+    for (auto &p : imported_caps )
+      peer_caps_ids[p.first] = it->second.at(p.first).cap_id;
+
+    encode(imported_caps, ack->cap_bl);
+    encode(peer_caps_ids, ack->cap_bl);
+    mds->send_message_mds(ack, from);
+  }
+
+  in->auth_unpin(this);
+}
+
+Migrator::Migrator(MDSRank *m, MDCache *c) : mds(m), cache(c) {
+  max_export_size = g_conf().get_val<Option::size_t>("mds_max_export_size");
+  inject_session_race = g_conf().get_val<bool>("mds_inject_migrator_session_race");
+}
+
+void Migrator::handle_conf_change(const std::set<std::string>& changed, const MDSMap& mds_map)
+{
+  if (changed.count("mds_max_export_size"))
+    max_export_size = g_conf().get_val<Option::size_t>("mds_max_export_size");
+  if (changed.count("mds_inject_migrator_session_race")) {
+    inject_session_race = g_conf().get_val<bool>("mds_inject_migrator_session_race");
+    dout(0) << "mds_inject_migrator_session_race is " << inject_session_race << dendl;
+  }
+}