update sources to 12.2.7

[ceph.git] / ceph / src / mds / Migrator.cc

// -*- 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"

#include "messages/MExportDirDiscover.h"
#include "messages/MExportDirDiscoverAck.h"
#include "messages/MExportDirCancel.h"
#include "messages/MExportDirPrep.h"
#include "messages/MExportDirPrepAck.h"
#include "messages/MExportDir.h"
#include "messages/MExportDirAck.h"
#include "messages/MExportDirNotify.h"
#include "messages/MExportDirNotifyAck.h"
#include "messages/MExportDirFinish.h"

#include "messages/MExportCaps.h"
#include "messages/MExportCapsAck.h"
#include "messages/MGatherCaps.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 MDSInternalContextBase {
protected:
  Migrator *mig;
  MDSRank *get_mds() override {
    return mig->mds;
  }
public:
  explicit MigratorContext(Migrator *mig_) : mig(mig_) {
    assert(mig != NULL);
  }
};

class MigratorLogContext : public MDSLogContextBase {
protected:
  Migrator *mig;
  MDSRank *get_mds() override {
    return mig->mds;
  }
public:
  explicit MigratorLogContext(Migrator *mig_) : mig(mig_) {
    assert(mig != NULL);
  }
};

/* This function DOES put the passed message before returning*/
void Migrator::dispatch(Message *m)
{
  switch (m->get_type()) {
    // import
  case MSG_MDS_EXPORTDIRDISCOVER:
    handle_export_discover(static_cast<MExportDirDiscover*>(m));
    break;
  case MSG_MDS_EXPORTDIRPREP:
    handle_export_prep(static_cast<MExportDirPrep*>(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(static_cast<MExportDir*>(m));
    }
    break;
  case MSG_MDS_EXPORTDIRFINISH:
    handle_export_finish(static_cast<MExportDirFinish*>(m));
    break;
  case MSG_MDS_EXPORTDIRCANCEL:
    handle_export_cancel(static_cast<MExportDirCancel*>(m));
    break;

    // export 
  case MSG_MDS_EXPORTDIRDISCOVERACK:
    handle_export_discover_ack(static_cast<MExportDirDiscoverAck*>(m));
    break;
  case MSG_MDS_EXPORTDIRPREPACK:
    handle_export_prep_ack(static_cast<MExportDirPrepAck*>(m));
    break;
  case MSG_MDS_EXPORTDIRACK:
    handle_export_ack(static_cast<MExportDirAck*>(m));
    break;
  case MSG_MDS_EXPORTDIRNOTIFYACK:
    handle_export_notify_ack(static_cast<MExportDirNotifyAck*>(m));
    break;    

    // export 3rd party (dir_auth adjustments)
  case MSG_MDS_EXPORTDIRNOTIFY:
    handle_export_notify(static_cast<MExportDirNotify*>(m));
    break;

    // caps
  case MSG_MDS_EXPORTCAPS:
    handle_export_caps(static_cast<MExportCaps*>(m));
    break;
  case MSG_MDS_GATHERCAPS:
    handle_gather_caps(static_cast<MGatherCaps*>(m));
    break;

  default:
    derr << "migrator unknown message " << m->get_type() << dendl;
    assert(0 == "migrator unknown message");
  }
}


class C_MDC_EmptyImport : public MigratorContext {
  CDir *dir;
public:
  C_MDC_EmptyImport(Migrator *m, CDir *d) : MigratorContext(m), dir(d) {}
  void finish(int r) override {
    mig->export_empty_import(dir);
  }
};


void Migrator::export_empty_import(CDir *dir)
{
  dout(7) << "export_empty_import " << *dir << dendl;
  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;
    if (stat.last_cum_auth_pins != dir->get_cum_auth_pins()) {
      stat.last_cum_auth_pins = dir->get_cum_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);
  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;
    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(new MExportDirCancel(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(new MExportDirCancel(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);
    for (auto bd : it->second.residual_dirs) {
      bd->unfreeze_tree();
      cache->try_subtree_merge(bd);
    }
    if (notify_peer &&
	(!mds->is_cluster_degraded() ||
	 mds->mdsmap->is_clientreplay_or_active_or_stopping(it->second.peer))) // tell them.
      mds->send_message_mds(new MExportDirCancel(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_state.erase(it);
      dir->state_clear(CDir::STATE_EXPORTING);
      // send pending import_maps?
      cache->maybe_send_pending_resolves();
    }

    // drop locks
    if (state == EXPORT_LOCKING || state == EXPORT_DISCOVERING) {
      MDRequestRef mdr = static_cast<MDRequestImpl*>(mut.get());
      assert(mdr);
      if (mdr->more()->waiting_on_slave.empty())
	mds->mdcache->request_finish(mdr);
    } else if (mut) {
      mds->locker->drop_locks(mut.get());
      mut->cleanup();
    }

    cache->show_subtrees();

    maybe_do_queued_export();
  }
}

void Migrator::export_cancel_finish(CDir *dir)
{
  assert(dir->state_test(CDir::STATE_EXPORTING));
  dir->state_clear(CDir::STATE_EXPORTING);

  // 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();
}

// ==========================================================
// 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_state.erase(p);
	    export_cancel_finish(dir);
	  }
	}
      }
    }
    
    // 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:
	assert(diri);
	dout(10) << "import state=discovered : unpinning inode " << *diri << dendl;
	import_reverse_discovered(df, diri);
	break;

      case IMPORT_PREPPING:
	assert(dir);
	dout(10) << "import state=prepping : unpinning base+bounds " << *dir << dendl;
	import_reverse_prepping(dir, q->second);
	break;

      case IMPORT_PREPPED:
	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);
	  assert(g_conf->mds_kill_import_at != 10);
	}
	break;

      case IMPORT_LOGGINGSTART:
	assert(dir);
	dout(10) << "import state=loggingstart : reversing import on " << *dir << dendl;
	import_reverse(dir);
	break;

      case IMPORT_ACKING:
	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:
	assert(dir);
	dout(10) << "import state=finishing : finishing import on " << *dir << dendl;
	import_finish(dir, true);
	break;

      case IMPORT_ABORTING:
	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) {
	  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);
      assert(in);
      continue;
    }
    CDir *dir = cache->get_dirfrag(p->first);
    assert(dir);
    if (p->second.state == IMPORT_PREPPING)
      continue;
    if (p->second.state == IMPORT_ABORTING) {
      assert(!dir->is_ambiguous_dir_auth());
      assert(dir->get_dir_auth().first != mds->get_nodeid());
      continue;
    }
    assert(dir->is_ambiguous_dir_auth());
    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;
    assert(dir->is_ambiguous_dir_auth());
    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;
  while (!export_queue.empty() &&
	 export_state.size() <= 4) {
    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 *ex;   // dir i'm exporting
  uint64_t tid;
public:
  C_MDC_ExportFreeze(Migrator *m, CDir *e, uint64_t t) :
	MigratorContext(m), ex(e), tid(t) {
          assert(ex != NULL);
        }
  void finish(int r) override {
    if (r >= 0)
      mig->export_frozen(ex, tid);
  }
};


void Migrator::get_export_lock_set(CDir *dir, set<SimpleLock*>& locks)
{
  // path
  vector<CDentry*> trace;
  cache->make_trace(trace, dir->inode);
  for (vector<CDentry*>::iterator it = trace.begin();
       it != trace.end();
       ++it)
    locks.insert(&(*it)->lock);

  // prevent scatter gather race
  locks.insert(&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.
  set<CDir*> wouldbe_bounds;
  cache->get_wouldbe_subtree_bounds(dir, wouldbe_bounds);
  for (set<CDir*>::iterator p = wouldbe_bounds.begin(); p != wouldbe_bounds.end(); ++p)
    locks.insert(&(*p)->get_inode()->dirfragtreelock);
}


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);
  }
};


/** 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;
  assert(dir->is_auth());
  assert(dest != mds->get_nodeid());
   
  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;
    }
  } else {
    if (!mds->is_stopping() && !dir->inode->is_exportable(dest)) {
      dout(7) << "dir is export pinned" << 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())) {
	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(ceph_clock_now(), dest, -1);

  dir->auth_pin(this);
  dir->state_set(CDir::STATE_EXPORTING);

  MDRequestRef mdr = mds->mdcache->request_start_internal(CEPH_MDS_OP_EXPORTDIR);
  mdr->more()->export_dir = dir;

  assert(export_state.count(dir) == 0);
  export_state_t& stat = export_state[dir];
  stat.state = EXPORT_LOCKING;
  stat.peer = dest;
  stat.tid = mdr->reqid.tid;
  stat.mut = mdr;

  return mds->mdcache->dispatch_request(mdr);
}

void Migrator::dispatch_export_dir(MDRequestRef& mdr, int count)
{
  dout(7) << "dispatch_export_dir " << *mdr << dendl;

  CDir *dir = mdr->more()->export_dir;
  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;
    mds->mdcache->request_finish(mdr);
    return;
  }
  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?
  set<SimpleLock*> rdlocks;
  set<SimpleLock*> xlocks;
  set<SimpleLock*> wrlocks;
  get_export_lock_set(dir, rdlocks);
  // 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.
  wrlocks.insert(&dir->get_inode()->filelock);
  wrlocks.insert(&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, rdlocks, wrlocks, xlocks, NULL, NULL, true)) {
    if (mdr->aborted)
      export_try_cancel(dir);
    return;
  }

  assert(g_conf->mds_kill_export_at != 1);
  it->second.state = EXPORT_DISCOVERING;

  // send ExportDirDiscover (ask target)
  filepath path;
  dir->inode->make_path(path);
  MExportDirDiscover *discover = new MExportDirDiscover(dir->dirfrag(), path,
							mds->get_nodeid(),
							it->second.tid);
  mds->send_message_mds(discover, dest);
  assert(g_conf->mds_kill_export_at != 2);

  it->second.last_cum_auth_pins_change = ceph_clock_now();

  // start the freeze, but hold it up with an auth_pin.
  dir->freeze_tree();
  assert(dir->is_freezing_tree());
  dir->add_waiter(CDir::WAIT_FROZEN, new C_MDC_ExportFreeze(this, dir, it->second.tid));
}

/*
 * called on receipt of MExportDirDiscoverAck
 * the importer now has the directory's _inode_ in memory, and pinned.
 *
 * This function DOES put the passed message before returning
 */
void Migrator::handle_export_discover_ack(MExportDirDiscoverAck *m)
{
  CDir *dir = cache->get_dirfrag(m->get_dirfrag());
  mds_rank_t dest(m->get_source().num());
  utime_t now = ceph_clock_now();
  assert(dir);
  
  dout(7) << "export_discover_ack from " << m->get_source()
	  << " on " << *dir << dendl;

  mds->hit_export_target(now, 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 {
    assert(it->second.state == EXPORT_DISCOVERING);

    if (m->is_success()) {
      // release locks to avoid deadlock
      MDRequestRef mdr = static_cast<MDRequestImpl*>(it->second.mut.get());
      assert(mdr);
      mds->mdcache->request_finish(mdr);
      it->second.mut.reset();
      // freeze the subtree
      it->second.state = EXPORT_FREEZING;
      dir->auth_unpin(this);
      assert(g_conf->mds_kill_export_at != 3);

    } else {
      dout(7) << "peer failed to discover (not active?), canceling" << dendl;
      export_try_cancel(dir, false);
    }
  }
  
  m->put();  // done
}

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) {
    assert(dir != NULL);
  }
  void finish(int r) override {
    mig->export_sessions_flushed(dir, tid);
  }
};

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;
  }

  assert(it->second.state == EXPORT_PREPPING || it->second.state == EXPORT_WARNING);
  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;
  }

  assert(it->second.state == EXPORT_FREEZING);
  assert(dir->is_frozen_tree_root());
  assert(dir->get_cum_auth_pins() == 0);

  CInode *diri = dir->get_inode();

  // ok, try to grab all my locks.
  set<SimpleLock*> rdlocks;
  get_export_lock_set(dir, rdlocks);
  if ((diri->is_auth() && diri->is_frozen()) ||
      !mds->locker->can_rdlock_set(rdlocks) ||
      !diri->filelock.can_wrlock(-1) ||
      !diri->nestlock.can_wrlock(-1)) {
    dout(7) << "export_dir couldn't acquire all needed locks, failing. "
	    << *dir << dendl;
    // .. unwind ..
    dir->unfreeze_tree();
    cache->try_subtree_merge(dir);

    mds->send_message_mds(new MExportDirCancel(dir->dirfrag(), it->second.tid), it->second.peer);
    export_state.erase(it);

    dir->state_clear(CDir::STATE_EXPORTING);
    cache->maybe_send_pending_resolves();
    return;
  }

  it->second.mut = new MutationImpl();
  if (diri->is_auth())
    it->second.mut->auth_pin(diri);
  mds->locker->rdlock_take_set(rdlocks, 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.
  assert(dir->get_dir_auth() == mds_authority_t(mds->get_nodeid(), mds->get_nodeid()));

  set<client_t> export_client_set;
  check_export_size(dir, it->second, export_client_set);

  // note the bounds.
  set<CDir*> bounds;
  cache->get_subtree_bounds(dir, bounds);

  // generate prep message, log entry.
  MExportDirPrep *prep = new MExportDirPrep(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.
    assert(bound->state_test(CDir::STATE_EXPORTBOUND));
    
    dout(7) << "  export bound " << *bound << dendl;
    prep->add_bound( bound->dirfrag() );

    // trace to bound
    bufferlist tracebl;
    CDir *cur = bound;

    char start = '-';
    if (it->second.residual_dirs.count(bound)) {
      start = 'f';
      cache->replicate_dir(bound, it->second.peer, tracebl);
      dout(7) << "  added " << *bound << dendl;
    }

    while (1) {
      // don't repeat inodes
      if (inodes_added.count(cur->inode->ino()))
	break;
      inodes_added.insert(cur->inode->ino());

      // prepend dentry + inode
      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
  assert(it->second.warning_ack_waiting.empty());

  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::check_export_size(CDir *dir, export_state_t& stat, set<client_t>& client_set)
{
  const unsigned frag_size = 800;
  const unsigned inode_size = 1000;
  const unsigned cap_size = 80;
  const unsigned link_size = 10;
  const unsigned null_size = 1;

  uint64_t max_size = g_conf->get_val<uint64_t>("mds_max_export_size");
  uint64_t approx_size = 0;

  list<CDir*> dfs;
  dfs.push_back(dir);
  while (!dfs.empty()) {
    CDir *dir = dfs.front();
    dfs.pop_front();

    approx_size += frag_size;
    for (auto &p : *dir) {
      CDentry *dn = p.second;
      if (dn->get_linkage()->is_null()) {
	approx_size += null_size;
	continue;
      }
      if (dn->get_linkage()->is_remote()) {
	approx_size += link_size;
	continue;
      }

      approx_size += inode_size;
      CInode *in = dn->get_linkage()->get_inode();
      if (in->is_dir()) {
	// directory?
	list<CDir*> ls;
	in->get_dirfrags(ls);
	for (auto q : ls) {
	  if (q->is_subtree_root()) {
	    q->state_set(CDir::STATE_EXPORTBOUND);
	    q->get(CDir::PIN_EXPORTBOUND);
	  } else {
	    // include nested dirfrag
	    assert(q->get_dir_auth().first == CDIR_AUTH_PARENT);
	    dfs.push_front(q);
	  }
	}
      }
      for (map<client_t, Capability*>::iterator q = in->client_caps.begin();
	   q != in->client_caps.end();
	   ++q) {
	approx_size += cap_size;
	client_set.insert(q->first);
      }
    }

    if (approx_size >= max_size)
      break;
  }

  while (!dfs.empty()) {
    CDir *dir = dfs.front();
    dfs.pop_front();

    dout(7) << "check_export_size: creating bound " << *dir << dendl;
    assert(dir->is_auth());
    dir->state_set(CDir::STATE_EXPORTBOUND);
    dir->get(CDir::PIN_EXPORTBOUND);

    mds->mdcache->adjust_subtree_auth(dir, mds->get_nodeid());
    // Another choice here is finishing all WAIT_UNFREEZE contexts and keeping
    // the newly created subtree unfreeze.
    dir->_freeze_tree();

    stat.residual_dirs.insert(dir);
  }
}

void Migrator::get_export_client_set(CInode *in, set<client_t>& client_set)
{
  for (map<client_t, Capability*>::iterator q = in->client_caps.begin();
      q != in->client_caps.end();
      ++q)
    client_set.insert(q->first);
}

/* This function DOES put the passed message before returning*/
void Migrator::handle_export_prep_ack(MExportDirPrepAck *m)
{
  CDir *dir = cache->get_dirfrag(m->get_dirfrag());
  mds_rank_t dest(m->get_source().num());
  utime_t now = ceph_clock_now();
  assert(dir);

  dout(7) << "export_prep_ack " << *dir << dendl;

  mds->hit_export_target(now, 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;
    m->put();
    return;
  }
  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);
    m->put();
    return;
  }

  assert (g_conf->mds_kill_export_at != 5);
  // send warnings
  set<CDir*> bounds;
  cache->get_subtree_bounds(dir, bounds);

  assert(it->second.warning_ack_waiting.empty() ||
         (it->second.warning_ack_waiting.size() == 1 &&
	  it->second.warning_ack_waiting.count(MDS_RANK_NONE) > 0));
  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!

    MExportDirNotify *notify = new MExportDirNotify(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 (set<CDir*>::iterator q = bounds.begin(); q != bounds.end(); ++q)
      notify->get_bounds().push_back((*q)->dirfrag());
    mds->send_message_mds(notify, p.first);
    
  }

  it->second.state = EXPORT_WARNING;

  assert(g_conf->mds_kill_export_at != 6);
  // nobody to warn?
  if (it->second.warning_ack_waiting.empty())
    export_go(dir);  // start export.
    
  // done.
  m->put();
}


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) {
      assert(dir != NULL);
    }
  void finish(int r) override {
    mig->export_go_synced(dir, tid);
  }
};

void Migrator::export_go(CDir *dir)
{
  auto it = export_state.find(dir);
  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;
  }
  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;
  assert(g_conf->mds_kill_export_at != 7);

  assert(dir->is_frozen_tree_root());
  assert(dir->get_cum_auth_pins() == 0);

  // set ambiguous auth
  cache->adjust_subtree_auth(dir, mds->get_nodeid(), dest);

  // take away the popularity we're sending.
  utime_t now = ceph_clock_now();
  mds->balancer->subtract_export(dir, now);
  
  // fill export message with cache data
  MExportDir *req = new MExportDir(dir->dirfrag(), it->second.tid);
  map<client_t,entity_inst_t> exported_client_map;
  uint64_t num_exported_inodes = encode_export_dir(req->export_data,
					      dir,   // recur start point
					      exported_client_map,
					      now);
  ::encode(exported_client_map, req->client_map,
           mds->mdsmap->get_up_features());

  // 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);
  assert(g_conf->mds_kill_export_at != 8);

  mds->hit_export_target(now, 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)
{
  dout(7) << "encode_export_inode " << *in << dendl;
  assert(!in->is_replica(mds->get_nodeid()));

  // relax locks?
  if (!in->is_replicated()) {
    in->replicate_relax_locks();
    dout(20) << " did replicate_relax_locks, now " << *in << dendl;
  }

  ::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);
}

void Migrator::encode_export_inode_caps(CInode *in, bool auth_cap, bufferlist& bl,
					map<client_t,entity_inst_t>& exported_client_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 (map<client_t, Capability*>::iterator it = in->client_caps.begin();
       it != in->client_caps.end();
       ++it) 
    exported_client_map[it->first] = mds->sessionmap.get_inst(entity_name_t::CLIENT(it->first.v));
}

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 (map<client_t, Capability*>::iterator it = in->client_caps.begin();
       it != in->client_caps.end();
       ++it) {
    Capability *cap = it->second;
    dout(7) << "finish_export_inode_caps telling client." << it->first
	    << " exported caps on " << *in << dendl;
    MClientCaps *m = new MClientCaps(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(it->first);
    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, it->first);
  }
  in->clear_client_caps_after_export();
  mds->locker->eval(in, CEPH_CAP_LOCKS);
}

void Migrator::finish_export_inode(CInode *in, utime_t now, mds_rank_t peer,
				   map<client_t,Capability::Import>& peer_imported,
				   list<MDSInternalContextBase*>& 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
  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->item_open_file.remove_myself();

  in->clear_dirty_parent();

  in->clear_file_locks();

  // waiters
  in->take_waiting(CInode::WAIT_ANY_MASK, finished);

  in->finish_export(now);
  
  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,
				utime_t now)
{
  uint64_t num_exported = 0;

  dout(7) << "encode_export_dir " << *dir << " " << dir->get_num_head_items() << " head items" << dendl;
  
  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();
    
    if (!dn->is_replicated())
      dn->lock.replicate_relax();

    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);  // 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
	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, now);

  return num_exported;
}

void Migrator::finish_export_dir(CDir *dir, utime_t now, mds_rank_t peer,
				 map<inodeno_t,map<client_t,Capability::Import> >& peer_imported,
				 list<MDSInternalContextBase*>& finished, int *num_dentries)
{
  dout(10) << "finish_export_dir " << *dir << dendl;

  // release open_by 
  dir->clear_replica_map();

  // mark
  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(now);

  // 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, now, 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, now, 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.
 *
 * This function DOES put the passed message before returning
 */
void Migrator::handle_export_ack(MExportDirAck *m)
{
  CDir *dir = cache->get_dirfrag(m->get_dirfrag());
  mds_rank_t dest(m->get_source().num());
  utime_t now = ceph_clock_now();
  assert(dir);
  assert(dir->is_frozen_tree_root());  // i'm exporting!

  // yay!
  dout(7) << "handle_export_ack " << *dir << dendl;

  mds->hit_export_target(now, dest, -1);

  map<CDir*,export_state_t>::iterator it = export_state.find(dir);
  assert(it != export_state.end());
  assert(it->second.state == EXPORT_EXPORTING);
  assert(it->second.tid == m->get_tid());

  bufferlist::iterator bp = m->imported_caps.begin();
  ::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);
  
  m->put();
}

void Migrator::export_notify_abort(CDir *dir, export_state_t& stat, set<CDir*>& bounds)
{
  dout(7) << "export_notify_abort " << *dir << dendl;

  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) {
    MExportDirNotify *notify = new MExportDirNotify(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);
  for (auto bd : stat.residual_dirs) {
    bd->unfreeze_tree();
    cache->try_subtree_merge(bd);
  }

  // revoke/resume stale caps
  for (auto in : to_eval) {
    bool need_issue = false;
    for (auto& p : in->get_client_caps()) {
      Capability *cap = p.second;
      if (cap->is_stale()) {
	mds->locker->revoke_stale_caps(cap);
      } else {
	need_issue = true;
      }
    }
    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) {
    MExportDirNotify *notify = new MExportDirNotify(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(new MExportDirFinish(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.
 *
 * This function DOES put the passed message before returning
 */
void Migrator::handle_export_notify_ack(MExportDirNotifyAck *m)
{
  CDir *dir = cache->get_dirfrag(m->get_dirfrag());
  mds_rank_t dest(m->get_source().num());
  utime_t now = ceph_clock_now();
  assert(dir);
  mds_rank_t from = mds_rank_t(m->get_source().num());

  mds->hit_export_target(now, 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_state.erase(export_state_entry);
	export_cancel_finish(dir);
      }
    }
  }
  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;
	assert(stat.bystanders.count(from));
	stat.bystanders.erase(from);
	if (stat.bystanders.empty())
	  import_reverse_unfreeze(dir);
      }
    }
  }

  m->put();
}

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(new MExportDirFinish(dir->dirfrag(), true, it->second.tid), it->second.peer);
  } else {
    dout(7) << "not sending MExportDirFinish last, dest has failed" << dendl;
  }
  assert(g_conf->mds_kill_export_at != 13);
  
  // finish export (adjust local cache state)
  int num_dentries = 0;
  list<MDSInternalContextBase*> finished;
  finish_export_dir(dir, ceph_clock_now(), it->second.peer,
		    it->second.peer_imported, finished, &num_dentries);

  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);
  for (auto bd : it->second.residual_dirs) {
    export_queue.push_front(pair<dirfrag_t,mds_rank_t>(bd->dirfrag(), it->second.peer));
    bd->take_waiting(CDir::WAIT_ANY_MASK, finished);
    bd->unfreeze_tree();
    cache->try_subtree_merge(bd);
  }

  // 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 = it->second.mut;
  // remove from exporting list, clean up state
  export_state.erase(it);
  dir->state_clear(CDir::STATE_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();
  }
  
  maybe_do_queued_export();
}








// ==========================================================
// IMPORT

void Migrator::handle_export_discover(MExportDirDiscover *m)
{
  mds_rank_t from = m->get_source_mds();
  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(new MExportDirDiscoverAck(df, m->get_tid(), false), from);
    m->put();
    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 (!m->started) {
    assert(it == import_state.end());
    m->started = true;
    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;
      m->put();
      return;
    }
    assert(it->second.state == IMPORT_DISCOVERING);
    p_state = &it->second;
  }

  if (!mds->mdcache->is_open()) {
    dout(5) << " waiting for root" << dendl;
    mds->mdcache->wait_for_open(new C_MDS_RetryMessage(mds, m));
    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, m, NULL, fpath, &trace, NULL, MDS_TRAVERSE_DISCOVER);
    if (r > 0) return;
    if (r < 0) {
      dout(7) << "handle_export_discover_2 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)
  assert(in->is_dir());
  in->get(CInode::PIN_IMPORTING);

  // reply
  dout(7) << " sending export_discover_ack on " << *in << dendl;
  mds->send_message_mds(new MExportDirDiscoverAck(df, m->get_tid()), p_state->peer);
  m->put();
  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);
}

/* This function DOES put the passed message before returning*/
void Migrator::handle_export_cancel(MExportDirCancel *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()) {
    assert(0 == "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);
    assert(in);
    import_reverse_discovered(df, in);
  } else if (it->second.state == IMPORT_PREPPING) {
    CDir *dir = mds->mdcache->get_dirfrag(df);
    assert(dir);
    import_reverse_prepping(dir, it->second);
  } else if (it->second.state == IMPORT_PREPPED) {
    CDir *dir = mds->mdcache->get_dirfrag(df);
    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 {
    assert(0 == "got export_cancel in weird state");
  }
  m->put();
}

/* This function DOES put the passed message before returning*/
void Migrator::handle_export_prep(MExportDirPrep *m)
{
  mds_rank_t oldauth = mds_rank_t(m->get_source().num());
  assert(oldauth != mds->get_nodeid());

  CDir *dir;
  CInode *diri;
  list<MDSInternalContextBase*> finished;

  // assimilate root dir.
  map<dirfrag_t,import_state_t>::iterator it = import_state.find(m->get_dirfrag());
  if (!m->did_assim()) {
    assert(it != import_state.end());
    assert(it->second.state == IMPORT_DISCOVERED);
    assert(it->second.peer == oldauth);
    diri = cache->get_inode(m->get_dirfrag().ino);
    assert(diri);
    bufferlist::iterator p = m->basedir.begin();
    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;
      m->put();
      return;
    }
    assert(it->second.state == IMPORT_PREPPING);
    assert(it->second.peer == oldauth);

    dir = cache->get_dirfrag(m->get_dirfrag());
    assert(dir);
    dout(7) << "handle_export_prep on " << *dir << " (subsequent pass)" << dendl;
    diri = dir->get_inode();
  }
  assert(dir->is_auth() == false);

  cache->show_subtrees();

  // build import bound map
  map<inodeno_t, fragset_t> import_bound_fragset;
  for (list<dirfrag_t>::iterator p = m->get_bounds().begin();
       p != m->get_bounds().end();
       ++p) {
    dout(10) << " bound " << *p << dendl;
    import_bound_fragset[p->ino].insert(p->frag);
  }

  // assimilate contents?
  if (!m->did_assim()) {
    dout(7) << "doing assim on " << *dir << dendl;
    m->mark_assim();  // only do this the first time!

    // change import state
    it->second.state = IMPORT_PREPPING;
    it->second.bound_ls = m->get_bounds();
    it->second.bystanders = m->get_bystanders();
    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 (list<bufferlist>::iterator p = m->traces.begin();
	 p != m->traces.end();
	 ++p) {
      bufferlist::iterator q = p->begin();
      dirfrag_t df;
      ::decode(df, q);
      char start;
      ::decode(start, q);
      dout(10) << " trace from " << df << " start " << start << " len " << p->length() << dendl;

      CDir *cur = 0;
      if (start == 'd') {
	cur = cache->get_dirfrag(df);
	assert(cur);
	dout(10) << "  had " << *cur << dendl;
      } else if (start == 'f') {
	CInode *in = cache->get_inode(df.ino);
	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
	assert(0 == "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);
      assert(in);
      in->get_stickydirs();
      dout(7) << " set stickydirs on bound inode " << *in << dendl;
    }

  } else {
    dout(7) << " not doing assim on " << *dir << dendl;
  }

  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);
      assert(in);

      // map fragset into a frag_t list, based on the inode fragtree
      list<frag_t> fglist;
      for (set<frag_t>::iterator q = p->second.begin(); q != p->second.end(); ++q)
	in->dirfragtree.get_leaves_under(*q, fglist);
      dout(10) << " bound inode " << p->first << " fragset " << p->second << " maps to " << fglist << dendl;

      for (list<frag_t>::iterator q = fglist.begin();
	   q != fglist.end();
	   ++q) {
	CDir *bound = cache->get_dirfrag(dirfrag_t(p->first, *q));
	if (!bound) {
	  dout(7) << "  opening bounding dirfrag " << *q << " on " << *in << dendl;
	  cache->open_remote_dirfrag(in, *q,
	      new C_MDS_RetryMessage(mds, m));
	  return;
	}

	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);
      }
    }

    dout(7) << " all ready, noting auth and freezing import region" << dendl;

    if (!mds->mdcache->is_readonly() &&
	dir->get_inode()->filelock.can_wrlock(-1) &&
	dir->get_inode()->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(new MExportDirPrepAck(dir->dirfrag(), success, m->get_tid()), m->get_connection());

  assert(g_conf->mds_kill_import_at != 4);
  // done 
  m->put();
}




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) {
  }
  void finish(int r) override {
    mig->import_logged_start(df, dir, from, imported_session_map);
  }
};

/* This function DOES put the passed message before returning*/
void Migrator::handle_export_dir(MExportDir *m)
{
  assert (g_conf->mds_kill_import_at != 5);
  CDir *dir = cache->get_dirfrag(m->dirfrag);
  assert(dir);

  mds_rank_t oldauth = mds_rank_t(m->get_source().num());
  dout(7) << "handle_export_dir importing " << *dir << " from " << oldauth << dendl;

  assert(!dir->is_auth());
  
  map<dirfrag_t,import_state_t>::iterator it = import_state.find(m->dirfrag);
  assert(it != import_state.end());
  assert(it->second.state == IMPORT_PREPPED);
  assert(it->second.tid == m->get_tid());
  assert(it->second.peer == oldauth);

  utime_t now = ceph_clock_now();

  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
  bufferlist::iterator cmp = m->client_map.begin();
  map<client_t,entity_inst_t> client_map;
  decode(client_map, cmp);
  assert(cmp.end());
  le->cmapv = mds->server->prepare_force_open_sessions(client_map, onlogged->imported_session_map);
  encode(client_map, le->client_map, mds->mdsmap->get_up_features());

  bufferlist::iterator blp = m->export_data.begin();
  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,
			now);
  }
  dout(10) << " " << m->bounds.size() << " imported bounds" << dendl;
  
  // include bounds in EImportStart
  set<CDir*> import_bounds;
  for (vector<dirfrag_t>::iterator p = m->bounds.begin();
       p != m->bounds.end();
       ++p) {
    CDir *bd = cache->get_dirfrag(*p);
    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, now);

  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);
  }

  m->put();
}


/*
 * 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);
    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) {
      assert(bd->state_test(CDir::STATE_IMPORTBOUND));
      bd->put(CDir::PIN_IMPORTBOUND);
      bd->state_clear(CDir::STATE_IMPORTBOUND);
    }
  }
}


/*
 * 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.
  assert(dir->is_subtree_root());
  if (mds->is_resolve())
    cache->trim_non_auth_subtree(dir);

  cache->adjust_subtree_auth(dir, stat.peer);

  C_ContextsBase<MDSInternalContextBase, MDSInternalContextGather> *fin = new C_ContextsBase<MDSInternalContextBase, MDSInternalContextGather>(g_ceph_context);
  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
    assert(cur->is_auth());
    cur->state_clear(CDir::STATE_AUTH);
    cur->remove_bloom();
    cur->clear_replica_map();
    cur->set_replica_nonce(CDir::EXPORT_NONCE);
    if (cur->is_dirty())
      cur->mark_clean();

    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) {
	  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) {
    MExportDirNotify *notify =
      new MExportDirNotify(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;
    }
    MExportDirNotify *notify =
      new MExportDirNotify(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;
  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());
  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)
{
  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;
  }

  dout(7) << "import_logged " << *dir << dendl;

  // 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);

  MExportDirAck *ack = new MExportDirAck(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();
}

/* This function DOES put the passed message before returning*/
void Migrator::handle_export_finish(MExportDirFinish *m)
{
  CDir *dir = cache->get_dirfrag(m->get_dirfrag());
  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());
  assert(it != import_state.end());
  assert(it->second.tid == m->get_tid());

  import_finish(dir, false, m->is_last());

  m->put();
}

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());
  assert(it != import_state.end());
  assert(it->second.state == IMPORT_ACKING || it->second.state == IMPORT_FINISHING);

  if (it->second.state == IMPORT_ACKING) {
    assert(dir->is_auth());
    cache->adjust_subtree_auth(dir, mds->get_nodeid(), mds->get_nodeid());
  }

  // log finish
  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;
      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);
	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) {
    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::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) {
    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());
}

void Migrator::decode_import_inode_caps(CInode *in, bool auth_cap,
					bufferlist::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)
    ::decode(in->get_mds_caps_wanted(), blp);
  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();
    }

    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::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, utime_t now)
{
  // set up dir
  dirfrag_t df;
  ::decode(df, blp);

  CInode *diri = cache->get_inode(df.ino);
  assert(diri);
  CDir *dir = diri->get_or_open_dirfrag(mds->mdcache, df.frag);
  assert(dir);
  
  dout(7) << "decode_import_dir " << *dir << dendl;

  // assimilate state
  dir->decode_import(blp, now, 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.
  list<MDSInternalContextBase*> waiters;
  
  dir->take_waiting(CDir::WAIT_ANY_MASK, waiters);
  for (list<MDSInternalContextBase*>::iterator it = waiters.begin();
       it != waiters.end();
       ++it) 
    import_root->add_waiter(CDir::WAIT_UNFREEZE, *it);  // 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
      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()) {
	assert(dn->get_linkage()->get_remote_ino() == ino);
      } else {
	dir->link_remote_inode(dn, ino, d_type);
      }
    }
    else if (icode == 'I') {
      // inode
      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

/* This function DOES put the passed message before returning*/
void Migrator::handle_export_notify(MExportDirNotify *m)
{
  if (!(mds->is_clientreplay() || mds->is_active() || mds->is_stopping())) {
    m->put();
    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(new MExportDirNotifyAck(m->get_dirfrag(), m->get_tid(), m->get_new_auth()), from);
  } else {
    // aborted.  no ack.
    dout(7) << "handle_export_notify no ack requested" << dendl;
  }
  
  m->put();
}

/** cap exports **/
void Migrator::export_caps(CInode *in)
{
  mds_rank_t dest = in->authority().first;
  dout(7) << "export_caps to mds." << dest << " " << *in << dendl;

  assert(in->is_any_caps());
  assert(!in->is_auth());
  assert(!in->is_ambiguous_auth());
  assert(!in->state_test(CInode::STATE_EXPORTINGCAPS));

  MExportCaps *ex = new MExportCaps;
  ex->ino = in->ino();

  encode_export_inode_caps(in, false, ex->cap_bl, ex->client_map);

  mds->send_message_mds(ex, dest);
}

void Migrator::handle_gather_caps(MGatherCaps *m)
{
  CInode *in = cache->get_inode(m->ino);

  if (!in)
    goto out;

  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);

out:
  m->put();
}

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);
  }  
};

/* This function DOES put the passed message before returning*/
void Migrator::handle_export_caps(MExportCaps *ex)
{
  dout(10) << "handle_export_caps " << *ex << " from " << ex->get_source() << dendl;
  CInode *in = cache->get_inode(ex->ino);
  
  assert(in);
  assert(in->is_auth());

  // FIXME
  if (!in->can_auth_pin()) {
    ex->put();
    return;
  }

  in->auth_pin(this);

  map<client_t,entity_inst_t> client_map;
  client_map.swap(ex->client_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,
							  finish->imported_session_map);
  // decode new caps
  bufferlist::iterator blp = ex->cap_bl.begin();
  decode_import_inode_caps(in, false, blp, finish->peer_exports);
  assert(!finish->peer_exports.empty());   // thus, inode is pinned.

  // journal open client sessions
  
  ESessions *le = new ESessions(pv, client_map);
  mds->mdlog->start_submit_entry(le, finish);
  mds->mdlog->flush();

  ex->put();
}


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()
  assert(in->is_auth());

  // force open client sessions and finish cap import
  mds->server->finish_force_open_sessions(imported_session_map);

  map<client_t,Capability::Import> imported_caps;

  auto it = peer_exports.find(in);
  assert(it != peer_exports.end());

  // clients will release caps from the exporter when they receive the cap import message.
  finish_import_inode_caps(in, from, false, imported_session_map, it->second, imported_caps);
  mds->locker->eval(in, CEPH_CAP_LOCKS, true);
  in->auth_unpin(this);
}

void Migrator::handle_conf_change(const struct md_config_t *conf,
                                  const std::set <std::string> &changed,
                                  const MDSMap &mds_map)
{
  if (changed.count("mds_inject_migrator_session_race")) {
    inject_session_race = conf->get_val<bool>("mds_inject_migrator_session_race");
    dout(0) << "mds_inject_migrator_session_race is " << inject_session_race << dendl;
  }
}