update ceph source to reef 18.2.1

[ceph.git] / ceph / src / mon / MDSMonitor.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 <regex>
#include <sstream>
#include <boost/utility.hpp>

#include "MDSMonitor.h"
#include "FSCommands.h"
#include "Monitor.h"
#include "MonitorDBStore.h"
#include "OSDMonitor.h"

#include "common/strtol.h"
#include "common/perf_counters.h"
#include "common/config.h"
#include "common/cmdparse.h"
#include "messages/MMDSMap.h"
#include "messages/MFSMap.h"
#include "messages/MFSMapUser.h"
#include "messages/MMDSLoadTargets.h"
#include "messages/MMonCommand.h"
#include "messages/MGenericMessage.h"

#include "include/ceph_assert.h"
#include "include/str_list.h"
#include "include/stringify.h"
#include "mds/mdstypes.h"
#include "Session.h"

using namespace TOPNSPC::common;

using std::dec;
using std::hex;
using std::list;
using std::map;
using std::make_pair;
using std::ostream;
using std::ostringstream;
using std::pair;
using std::set;
using std::string;
using std::string_view;
using std::stringstream;
using std::to_string;
using std::vector;

using ceph::bufferlist;
using ceph::decode;
using ceph::encode;
using ceph::ErasureCodeInterfaceRef;
using ceph::ErasureCodeProfile;
using ceph::Formatter;
using ceph::JSONFormatter;
using ceph::make_message;
using ceph::mono_clock;
using ceph::mono_time;

#define dout_subsys ceph_subsys_mon
#undef dout_prefix
#define dout_prefix _prefix(_dout, mon, get_fsmap())
static ostream& _prefix(std::ostream *_dout, Monitor &mon, const FSMap& fsmap) {
  return *_dout << "mon." << mon.name << "@" << mon.rank
		<< "(" << mon.get_state_name()
		<< ").mds e" << fsmap.get_epoch() << " ";
}

static const string MDS_METADATA_PREFIX("mds_metadata");
static const string MDS_HEALTH_PREFIX("mds_health");


/*
 * Specialized implementation of cmd_getval to allow us to parse
 * out strongly-typedef'd types
 */
namespace TOPNSPC::common {
template<> bool cmd_getval(const cmdmap_t& cmdmap,
			   std::string_view k, mds_gid_t &val)
{
  return cmd_getval(cmdmap, k, (int64_t&)val);
}

template<> bool cmd_getval(const cmdmap_t& cmdmap,
			   std::string_view k, mds_rank_t &val)
{
  return cmd_getval(cmdmap, k, (int64_t&)val);
}

template<> bool cmd_getval(const cmdmap_t& cmdmap,
			   std::string_view k, MDSMap::DaemonState &val)
{
  return cmd_getval(cmdmap, k, (int64_t&)val);
}
}
// my methods

template <int dblV>
void MDSMonitor::print_map(const FSMap& m)
{
  dout(dblV) << "print_map\n";
  m.print(*_dout);
  *_dout << dendl;
}

// service methods
void MDSMonitor::create_initial()
{
  dout(10) << "create_initial" << dendl;
}

void MDSMonitor::get_store_prefixes(std::set<string>& s) const
{
  s.insert(service_name);
  s.insert(MDS_METADATA_PREFIX);
  s.insert(MDS_HEALTH_PREFIX);
}

void MDSMonitor::update_from_paxos(bool *need_bootstrap)
{
  version_t version = get_last_committed();
  if (version == get_fsmap().epoch)
    return;

  dout(10) << __func__ << " version " << version
	   << ", my e " << get_fsmap().epoch << dendl;
  ceph_assert(version > get_fsmap().epoch);

  load_health();

  // read and decode
  bufferlist fsmap_bl;
  fsmap_bl.clear();
  int err = get_version(version, fsmap_bl);
  ceph_assert(err == 0);

  ceph_assert(fsmap_bl.length() > 0);
  dout(10) << __func__ << " got " << version << dendl;
  try {
    PaxosFSMap::decode(fsmap_bl);
  } catch (const ceph::buffer::malformed_input& e) {
    derr << "unable to decode FSMap: " << e.what() << dendl;
    throw;
  }

  // new map
  dout(0) << "new map" << dendl;
  print_map<0>(get_fsmap());
  if (!g_conf()->mon_mds_skip_sanity) {
    get_fsmap().sanity();
  }

  check_subs();
}

void MDSMonitor::init()
{
  (void)load_metadata(pending_metadata);
}

void MDSMonitor::create_pending()
{
  auto &fsmap = PaxosFSMap::create_pending();

  if (mon.osdmon()->is_readable()) {
    const auto &osdmap = mon.osdmon()->osdmap;
    fsmap.sanitize([&osdmap](int64_t pool){return osdmap.have_pg_pool(pool);});
  }

  dout(10) << "create_pending e" << fsmap.epoch << dendl;
}

void MDSMonitor::encode_pending(MonitorDBStore::TransactionRef t)
{
  auto &pending = get_pending_fsmap_writeable();
  auto &epoch = pending.epoch;

  dout(10) << "encode_pending e" << epoch << dendl;

  // print map iff 'debug mon = 30' or higher
  print_map<30>(pending);
  if (!g_conf()->mon_mds_skip_sanity) {
    pending.sanity(true);
  }

  // Set 'modified' on maps modified this epoch
  for (auto &p : pending.filesystems) {
    if (p.second->mds_map.epoch == epoch) {
      p.second->mds_map.modified = ceph_clock_now();
    }
  }

  // apply to paxos
  ceph_assert(get_last_committed() + 1 == pending.epoch);
  bufferlist pending_bl;
  pending.encode(pending_bl, mon.get_quorum_con_features());

  /* put everything in the transaction */
  put_version(t, pending.epoch, pending_bl);
  put_last_committed(t, pending.epoch);

  // Encode MDSHealth data
  for (std::map<uint64_t, MDSHealth>::iterator i = pending_daemon_health.begin();
      i != pending_daemon_health.end(); ++i) {
    bufferlist bl;
    i->second.encode(bl);
    t->put(MDS_HEALTH_PREFIX, stringify(i->first), bl);
  }

  for (std::set<uint64_t>::iterator i = pending_daemon_health_rm.begin();
      i != pending_daemon_health_rm.end(); ++i) {
    t->erase(MDS_HEALTH_PREFIX, stringify(*i));
  }
  pending_daemon_health_rm.clear();
  remove_from_metadata(pending, t);

  // health
  health_check_map_t new_checks;
  const auto &info_map = pending.get_mds_info();
  for (const auto &i : info_map) {
    const auto &gid = i.first;
    const auto &info = i.second;
    if (pending_daemon_health_rm.count(gid)) {
      continue;
    }
    MDSHealth health;
    auto p = pending_daemon_health.find(gid);
    if (p != pending_daemon_health.end()) {
      health = p->second;
    } else {
      bufferlist bl;
      mon.store->get(MDS_HEALTH_PREFIX, stringify(gid), bl);
      if (!bl.length()) {
	derr << "Missing health data for MDS " << gid << dendl;
	continue;
      }
      auto bl_i = bl.cbegin();
      health.decode(bl_i);
    }
    for (const auto &metric : health.metrics) {
      if (metric.type == MDS_HEALTH_DUMMY) {
        continue;
      }
      const auto rank = info.rank;
      health_check_t *check = &new_checks.get_or_add(
	mds_metric_name(metric.type),
	metric.sev,
	mds_metric_summary(metric.type),
	1);
      ostringstream ss;
      ss << "mds." << info.name << "(mds." << rank << "): " << metric.message;
      bool first = true;
      for (auto &p : metric.metadata) {
	if (first) {
	  ss << " ";
	} else {
	  ss << ", ";
        }
	ss << p.first << ": " << p.second;
        first = false;
      }
      check->detail.push_back(ss.str());
    }
  }
  pending.get_health_checks(&new_checks);
  for (auto& p : new_checks.checks) {
    p.second.summary = std::regex_replace(
      p.second.summary,
      std::regex("%num%"),
      stringify(p.second.detail.size()));
    p.second.summary = std::regex_replace(
      p.second.summary,
      std::regex("%plurals%"),
      p.second.detail.size() > 1 ? "s" : "");
    p.second.summary = std::regex_replace(
      p.second.summary,
      std::regex("%isorare%"),
      p.second.detail.size() > 1 ? "are" : "is");
    p.second.summary = std::regex_replace(
      p.second.summary,
      std::regex("%hasorhave%"),
      p.second.detail.size() > 1 ? "have" : "has");
  }
  encode_health(new_checks, t);
}

version_t MDSMonitor::get_trim_to() const
{
  version_t floor = 0;
  if (g_conf()->mon_mds_force_trim_to > 0 &&
      g_conf()->mon_mds_force_trim_to <= (int)get_last_committed()) {
    floor = g_conf()->mon_mds_force_trim_to;
    dout(10) << __func__ << " explicit mon_mds_force_trim_to = "
             << floor << dendl;
  }

  unsigned max = g_conf()->mon_max_mdsmap_epochs;
  version_t last = get_last_committed();

  if (last - get_first_committed() > max && floor < last - max) {
    floor = last-max;
  }

  dout(20) << __func__ << " = " << floor << dendl;
  return floor;
}

bool MDSMonitor::preprocess_query(MonOpRequestRef op)
{
  op->mark_mdsmon_event(__func__);
  auto m = op->get_req<PaxosServiceMessage>();
  dout(10) << "preprocess_query " << *m << " from " << m->get_orig_source()
	   << " " << m->get_orig_source_addrs() << dendl;

  switch (m->get_type()) {
    
  case MSG_MDS_BEACON:
    return preprocess_beacon(op);
    
  case MSG_MON_COMMAND:
    try {
      return preprocess_command(op);
    } catch (const bad_cmd_get& e) {
      bufferlist bl;
      mon.reply_command(op, -EINVAL, e.what(), bl, get_last_committed());
      return true;
    }

  case MSG_MDS_OFFLOAD_TARGETS:
    return preprocess_offload_targets(op);

  default:
    ceph_abort();
    return true;
  }
}

void MDSMonitor::_note_beacon(MMDSBeacon *m)
{
  mds_gid_t gid = mds_gid_t(m->get_global_id());
  version_t seq = m->get_seq();

  dout(5) << "_note_beacon " << *m << " noting time" << dendl;
  auto &beacon = last_beacon[gid];
  beacon.stamp = mono_clock::now();
  beacon.seq = seq;
}

bool MDSMonitor::preprocess_beacon(MonOpRequestRef op)
{
  op->mark_mdsmon_event(__func__);
  auto m = op->get_req<MMDSBeacon>();
  MDSMap::DaemonState state = m->get_state();
  mds_gid_t gid = m->get_global_id();
  version_t seq = m->get_seq();
  MDSMap::mds_info_t info;
  epoch_t effective_epoch = 0;

  const auto &fsmap = get_fsmap();

  // check privileges, ignore if fails
  MonSession *session = op->get_session();
  if (!session)
    goto ignore;
  if (!session->is_capable("mds", MON_CAP_X)) {
    dout(0) << "preprocess_beacon got MMDSBeacon from entity with insufficient privileges "
	    << session->caps << dendl;
    goto ignore;
  }

  if (m->get_fsid() != mon.monmap->fsid) {
    dout(0) << "preprocess_beacon on fsid " << m->get_fsid() << " != " << mon.monmap->fsid << dendl;
    goto ignore;
  }

  dout(5)  << "preprocess_beacon " << *m
	   << " from " << m->get_orig_source()
	   << " " << m->get_orig_source_addrs()
	   << " " << m->get_compat()
	   << dendl;

  // make sure the address has a port
  if (m->get_orig_source_addr().get_port() == 0) {
    dout(1) << " ignoring boot message without a port" << dendl;
    goto ignore;
  }

  // fw to leader?
  if (!is_leader())
    return false;

  // booted, but not in map?
  if (!fsmap.gid_exists(gid)) {
    if (state != MDSMap::STATE_BOOT) {
      dout(7) << "mds_beacon " << *m << " is not in fsmap (state "
              << ceph_mds_state_name(state) << ")" << dendl;

      /* We can't send an MDSMap this MDS was a part of because we no longer
       * know which FS it was part of. Nor does this matter. Sending an empty
       * MDSMap is sufficient for getting the MDS to respawn.
       */
      auto m = make_message<MMDSMap>(mon.monmap->fsid, MDSMap::create_null_mdsmap());
      mon.send_reply(op, m.detach());
      return true;
    } else {
      /* check if we've already recorded its entry in pending */
      const auto& pending = get_pending_fsmap();
      if (pending.gid_exists(gid)) {
        /* MDS is already booted. */
        goto ignore;
      } else {
        return false;  // not booted yet.
      }
    }
  }
  dout(10) << __func__ << ": GID exists in map: " << gid << dendl;
  info = fsmap.get_info_gid(gid);

  if (state == MDSMap::STATE_DNE) {
    return false;
  }

  // old seq?
  if (info.state_seq > seq) {
    dout(7) << "mds_beacon " << *m << " has old seq, ignoring" << dendl;
    goto ignore;
  }

  // Work out the latest epoch that this daemon should have seen
  {
    fs_cluster_id_t fscid = fsmap.mds_roles.at(gid);
    if (fscid == FS_CLUSTER_ID_NONE) {
      effective_epoch = fsmap.standby_epochs.at(gid);
    } else {
      effective_epoch = fsmap.get_filesystem(fscid)->mds_map.epoch;
    }
    if (effective_epoch != m->get_last_epoch_seen()) {
      dout(10) << "mds_beacon " << *m
               << " ignoring requested state, because mds hasn't seen latest map" << dendl;
      goto reply;
    }
  }

  if (info.laggy()) {
    _note_beacon(m);
    return false;  // no longer laggy, need to update map.
  }
  if (state == MDSMap::STATE_BOOT) {
    // ignore, already booted.
    goto ignore;
  }

  // did the join_fscid change
  if (m->get_fs().size()) {
    fs_cluster_id_t fscid = FS_CLUSTER_ID_NONE;
    auto f = fsmap.get_filesystem(m->get_fs());
    if (f) {
      fscid = f->fscid;
    }
    if (info.join_fscid != fscid) {
      dout(10) << __func__ << " standby mds_join_fs changed to " << fscid
               << " (" << m->get_fs() << ")" << dendl;
      _note_beacon(m);
      return false;
    }
  } else {
    if (info.join_fscid != FS_CLUSTER_ID_NONE) {
      dout(10) << __func__ << " standby mds_join_fs was cleared" << dendl;
      _note_beacon(m);
      return false;
    }
  }

  // is there a state change here?
  if (info.state != state) {
    _note_beacon(m);
    return false;
  }

  // Comparing known daemon health with m->get_health()
  // and return false (i.e. require proposal) if they
  // do not match, to update our stored
  if (!(pending_daemon_health[gid] == m->get_health())) {
    dout(10) << __func__ << " health metrics for gid " << gid << " were updated" << dendl;
    _note_beacon(m);
    return false;
  }

 reply:
  // note time and reply
  ceph_assert(effective_epoch > 0);
  _note_beacon(m);
  {
    auto beacon = make_message<MMDSBeacon>(mon.monmap->fsid,
        m->get_global_id(), m->get_name(), effective_epoch,
        state, seq, CEPH_FEATURES_SUPPORTED_DEFAULT);
    mon.send_reply(op, beacon.detach());
  }
  return true;

 ignore:
  // I won't reply this beacon, drop it.
  mon.no_reply(op);
  return true;
}

bool MDSMonitor::preprocess_offload_targets(MonOpRequestRef op)
{
  op->mark_mdsmon_event(__func__);
  auto m = op->get_req<MMDSLoadTargets>();
  dout(10) << "preprocess_offload_targets " << *m << " from " << m->get_orig_source() << dendl;

  const auto &fsmap = get_fsmap();
  
  // check privileges, ignore message if fails
  MonSession *session = op->get_session();
  if (!session)
    goto ignore;
  if (!session->is_capable("mds", MON_CAP_X)) {
    dout(0) << "preprocess_offload_targets got MMDSLoadTargets from entity with insufficient caps "
	    << session->caps << dendl;
    goto ignore;
  }

  if (fsmap.gid_exists(m->global_id) &&
      m->targets == fsmap.get_info_gid(m->global_id).export_targets)
    goto ignore;

  return false;

 ignore:
  mon.no_reply(op);
  return true;
}


bool MDSMonitor::prepare_update(MonOpRequestRef op)
{
  op->mark_mdsmon_event(__func__);
  auto m = op->get_req<PaxosServiceMessage>();
  dout(7) << "prepare_update " << *m << dendl;

  switch (m->get_type()) {
    
  case MSG_MDS_BEACON:
    return prepare_beacon(op);

  case MSG_MON_COMMAND:
    try {
      return prepare_command(op);
    } catch (const bad_cmd_get& e) {
      bufferlist bl;
      mon.reply_command(op, -EINVAL, e.what(), bl, get_last_committed());
      return false; /* nothing to propose */
    }

  case MSG_MDS_OFFLOAD_TARGETS:
    return prepare_offload_targets(op);
  
  default:
    ceph_abort();
  }

  return false; /* nothing to propose! */
}

bool MDSMonitor::prepare_beacon(MonOpRequestRef op)
{
  op->mark_mdsmon_event(__func__);
  auto m = op->get_req<MMDSBeacon>();
  // -- this is an update --
  dout(12) << "prepare_beacon " << *m << " from " << m->get_orig_source()
	   << " " << m->get_orig_source_addrs() << dendl;
  entity_addrvec_t addrs = m->get_orig_source_addrs();
  mds_gid_t gid = m->get_global_id();
  MDSMap::DaemonState state = m->get_state();
  version_t seq = m->get_seq();

  auto &pending = get_pending_fsmap_writeable();

  dout(15) << __func__ << " got health from gid " << gid << " with " << m->get_health().metrics.size() << " metrics." << dendl;

  // Calculate deltas of health metrics created and removed
  // Do this by type rather than MDSHealthMetric equality, because messages can
  // change a lot when they include e.g. a number of items.
  const auto &old_health = pending_daemon_health[gid].metrics;
  const auto &new_health = m->get_health().metrics;

  std::set<mds_metric_t> old_types;
  for (const auto &i : old_health) {
    old_types.insert(i.type);
  }

  std::set<mds_metric_t> new_types;
  for (const auto &i : new_health) {
    if (i.type == MDS_HEALTH_DUMMY) {
      continue;
    }
    new_types.insert(i.type);
  }

  for (const auto &new_metric: new_health) {
    if (new_metric.type == MDS_HEALTH_DUMMY) {
      continue;
    }
    if (old_types.count(new_metric.type) == 0) {
      dout(10) << "MDS health message (" << m->get_orig_source()
	       << "): " << new_metric.sev << " " << new_metric.message << dendl;
    }
  }

  // Log the disappearance of health messages at INFO
  for (const auto &old_metric : old_health) {
    if (new_types.count(old_metric.type) == 0) {
      mon.clog->info() << "MDS health message cleared ("
        << m->get_orig_source() << "): " << old_metric.message;
    }
  }

  // Store health
  pending_daemon_health[gid] = m->get_health();

  const auto& cs = m->get_compat();
  if (state == MDSMap::STATE_BOOT) {
    // zap previous instance of this name?
    if (g_conf()->mds_enforce_unique_name) {
      bool failed_mds = false;
      while (mds_gid_t existing = pending.find_mds_gid_by_name(m->get_name())) {
        if (!mon.osdmon()->is_writeable()) {
          mon.osdmon()->wait_for_writeable(op, new C_RetryMessage(this, op));
          return false;
        }
        const auto& existing_info = pending.get_info_gid(existing);
        mon.clog->info() << existing_info.human_name() << " restarted";
	fail_mds_gid(pending, existing);
        failed_mds = true;
      }
      if (failed_mds) {
        ceph_assert(mon.osdmon()->is_writeable());
        request_proposal(mon.osdmon());
      }
    }

    // Add this daemon to the map
    if (pending.mds_roles.count(gid) == 0) {
      MDSMap::mds_info_t new_info;
      new_info.global_id = gid;
      new_info.name = m->get_name();
      new_info.addrs = addrs;
      new_info.mds_features = m->get_mds_features();
      new_info.state = MDSMap::STATE_STANDBY;
      new_info.state_seq = seq;
      new_info.compat = cs;
      if (m->get_fs().size()) {
	fs_cluster_id_t fscid = FS_CLUSTER_ID_NONE;
	auto f = pending.get_filesystem(m->get_fs());
	if (f) {
	  fscid = f->fscid;
	}
        new_info.join_fscid = fscid;
      }
      pending.insert(new_info);
    }

    // initialize the beacon timer
    auto &beacon = last_beacon[gid];
    beacon.stamp = mono_clock::now();
    beacon.seq = seq;

    update_metadata(m->get_global_id(), m->get_sys_info());
  } else {
    // state update

    if (!pending.gid_exists(gid)) {
      /* gid has been removed from pending, send null map */
      dout(5) << "mds_beacon " << *m << " is not in fsmap (state "
              << ceph_mds_state_name(state) << ")" << dendl;

      /* We can't send an MDSMap this MDS was a part of because we no longer
       * know which FS it was part of. Nor does this matter. Sending an empty
       * MDSMap is sufficient for getting the MDS to respawn.
       */
      goto null;
    }

    const auto& info = pending.get_info_gid(gid);

    // did the reported compat change? That's illegal!
    if (cs.compare(info.compat) != 0) {
      if (!mon.osdmon()->is_writeable()) {
        mon.osdmon()->wait_for_writeable(op, new C_RetryMessage(this, op));
        return false;
      }
      mon.clog->warn() << info.human_name() << " compat changed unexpectedly";
      fail_mds_gid(pending, gid);
      request_proposal(mon.osdmon());
      return true;
    }

    if (state == MDSMap::STATE_DNE) {
      dout(1) << __func__ << ": DNE from " << info << dendl;
      goto evict;
    }

    // legal state change?
    if ((info.state == MDSMap::STATE_STANDBY && state != info.state) ||
        (info.state == MDSMap::STATE_STANDBY_REPLAY && state != info.state && state != MDSMap::STATE_DAMAGED)) {
      // Standby daemons should never modify their own state.
      // Except that standby-replay can indicate the rank is damaged due to failure to replay.
      // Reject any attempts to do so.
      derr << "standby " << gid << " attempted to change state to "
           << ceph_mds_state_name(state) << ", rejecting" << dendl;
      goto evict;
    } else if (info.state != MDSMap::STATE_STANDBY && state != info.state &&
               !MDSMap::state_transition_valid(info.state, state)) {
      // Validate state transitions for daemons that hold a rank
      derr << "daemon " << gid << " (rank " << info.rank << ") "
           << "reported invalid state transition "
           << ceph_mds_state_name(info.state) << " -> "
           << ceph_mds_state_name(state) << dendl;
      goto evict;
    }

    if (info.laggy()) {
      dout(1) << "prepare_beacon clearing laggy flag on " << addrs << dendl;
      pending.modify_daemon(info.global_id, [](auto& info)
        {
          info.clear_laggy();
        }
      );
    }

    dout(5)  << "prepare_beacon mds." << info.rank
	     << " " << ceph_mds_state_name(info.state)
	     << " -> " << ceph_mds_state_name(state)
	     << dendl;

    fs_cluster_id_t fscid = FS_CLUSTER_ID_NONE;
    if (m->get_fs().size()) {
      auto f = pending.get_filesystem(m->get_fs());
      if (f) {
        fscid = f->fscid;
      }
    }
    pending.modify_daemon(gid, [fscid](auto& info) {
      info.join_fscid = fscid;
    });

    if (state == MDSMap::STATE_STOPPED) {
      const auto fscid = pending.mds_roles.at(gid);
      const auto &fs = pending.get_filesystem(fscid);

      mon.clog->info() << info.human_name() << " finished "
                        << "stopping rank " << info.rank << " in filesystem "
                        << fs->mds_map.fs_name << " (now has "
                        << fs->mds_map.get_num_in_mds() - 1 << " ranks)";

      auto erased = pending.stop(gid);
      erased.push_back(gid);

      for (const auto& erased_gid : erased) {
        last_beacon.erase(erased_gid);
        if (pending_daemon_health.count(erased_gid)) {
          pending_daemon_health.erase(erased_gid);
          pending_daemon_health_rm.insert(erased_gid);
        }
      }
    } else if (state == MDSMap::STATE_DAMAGED) {
      if (!mon.osdmon()->is_writeable()) {
        dout(1) << __func__ << ": DAMAGED from rank " << info.rank
                << " waiting for osdmon writeable to blocklist it" << dendl;
        mon.osdmon()->wait_for_writeable(op, new C_RetryMessage(this, op));
        return false;
      }

      auto rank = info.rank;

      // Record this MDS rank as damaged, so that other daemons
      // won't try to run it.
      dout(0) << __func__ << ": marking rank " << rank << " damaged" << dendl;

      auto fs = pending.get_filesystem(gid);
      auto rankgid = fs->mds_map.get_gid(rank);
      auto rankinfo = pending.get_info_gid(rankgid);
      auto followergid = fs->mds_map.get_standby_replay(rank);

      ceph_assert(gid == rankgid || gid == followergid);

      utime_t until = ceph_clock_now();
      until += g_conf().get_val<double>("mon_mds_blocklist_interval");
      const auto blocklist_epoch = mon.osdmon()->blocklist(rankinfo.addrs, until);
      if (followergid != MDS_GID_NONE) {
        fail_mds_gid(pending, followergid);
        last_beacon.erase(followergid);
      }
      request_proposal(mon.osdmon());
      force_immediate_propose();
      pending.damaged(rankgid, blocklist_epoch);
      last_beacon.erase(rankgid);

      /* MDS expects beacon reply back */
    } else {
      if (info.state != MDSMap::STATE_ACTIVE && state == MDSMap::STATE_ACTIVE) {
        const auto &fscid = pending.mds_roles.at(gid);
        const auto &fs = pending.get_filesystem(fscid);
        mon.clog->info() << info.human_name() << " is now active in "
                          << "filesystem " << fs->mds_map.fs_name << " as rank "
                          << info.rank;
      }

      // Made it through special cases and validations, record the
      // daemon's reported state to the FSMap.
      pending.modify_daemon(gid, [state, seq](auto& info) {
        info.state = state;
        info.state_seq = seq;
      });
    }
  }

  dout(5) << "prepare_beacon pending map now:" << dendl;
  print_map(pending);
  
  wait_for_finished_proposal(op, new LambdaContext([op, this](int r){
    if (r >= 0)
      _updated(op);   // success
    else if (r == -ECANCELED) {
      mon.no_reply(op);
    } else {
      dispatch(op);        // try again
    }
  }));

  return true;

evict:
  if (!mon.osdmon()->is_writeable()) {
    dout(1) << __func__ << ": waiting for writeable OSDMap to evict" << dendl;
    mon.osdmon()->wait_for_writeable(op, new C_RetryMessage(this, op));
    return false;
  }

  fail_mds_gid(pending, gid);
  request_proposal(mon.osdmon());
  dout(5) << __func__ << ": pending map now:" << dendl;
  print_map(pending);

  goto null;

null:
  wait_for_finished_proposal(op, new LambdaContext([op, this](int r){
    if (r >= 0) {
      auto m = make_message<MMDSMap>(mon.monmap->fsid, MDSMap::create_null_mdsmap());
      mon.send_reply(op, m.detach());
    } else {
      dispatch(op);        // try again
    }
  }));

  return true;
}

bool MDSMonitor::prepare_offload_targets(MonOpRequestRef op)
{
  auto &pending = get_pending_fsmap_writeable();
  bool propose = false;

  op->mark_mdsmon_event(__func__);
  auto m = op->get_req<MMDSLoadTargets>();
  mds_gid_t gid = m->global_id;
  if (pending.gid_has_rank(gid)) {
    dout(10) << "prepare_offload_targets " << gid << " " << m->targets << dendl;
    pending.update_export_targets(gid, m->targets);
    propose = true;
  } else {
    dout(10) << "prepare_offload_targets " << gid << " not in map" << dendl;
  }
  mon.no_reply(op);
  return propose;
}

bool MDSMonitor::should_propose(double& delay)
{
  // delegate to PaxosService to assess whether we should propose
  return PaxosService::should_propose(delay);
}

void MDSMonitor::_updated(MonOpRequestRef op)
{
  const auto &fsmap = get_fsmap();
  op->mark_mdsmon_event(__func__);
  auto m = op->get_req<MMDSBeacon>();
  dout(10) << "_updated " << m->get_orig_source() << " " << *m << dendl;
  mon.clog->debug() << m->get_orig_source() << " "
		     << m->get_orig_source_addrs() << " "
		     << ceph_mds_state_name(m->get_state());

  if (m->get_state() == MDSMap::STATE_STOPPED) {
    // send the map manually (they're out of the map, so they won't get it automatic)
    auto m = make_message<MMDSMap>(mon.monmap->fsid, MDSMap::create_null_mdsmap());
    mon.send_reply(op, m.detach());
  } else {
    auto beacon = make_message<MMDSBeacon>(mon.monmap->fsid,
        m->get_global_id(), m->get_name(), fsmap.get_epoch(),
        m->get_state(), m->get_seq(), CEPH_FEATURES_SUPPORTED_DEFAULT);
    mon.send_reply(op, beacon.detach());
  }
}

void MDSMonitor::on_active()
{
  tick();

  if (is_leader()) {
    mon.clog->debug() << "fsmap " << get_fsmap();
  }
}

void MDSMonitor::dump_info(Formatter *f)
{
  f->open_object_section("fsmap");
  get_fsmap().dump(f);
  f->close_section();

  f->dump_unsigned("mdsmap_first_committed", get_first_committed());
  f->dump_unsigned("mdsmap_last_committed", get_last_committed());
}

bool MDSMonitor::preprocess_command(MonOpRequestRef op)
{
  op->mark_mdsmon_event(__func__);
  auto m = op->get_req<MMonCommand>();
  int r = -1;
  bufferlist rdata;
  stringstream ss, ds;

  cmdmap_t cmdmap;
  if (!cmdmap_from_json(m->cmd, &cmdmap, ss)) {
    // ss has reason for failure
    string rs = ss.str();
    mon.reply_command(op, -EINVAL, rs, rdata, get_last_committed());
    return true;
  }

  string prefix;
  cmd_getval(cmdmap, "prefix", prefix);
  string format = cmd_getval_or<string>(cmdmap, "format", "plain");
  std::unique_ptr<Formatter> f(Formatter::create(format));

  MonSession *session = op->get_session();
  if (!session) {
    mon.reply_command(op, -EACCES, "access denied", rdata, get_last_committed());
    return true;
  }

  // to use const qualifier filter fsmap beforehand
  FSMap _fsmap_copy = get_fsmap();
  _fsmap_copy.filter(session->get_allowed_fs_names());
  const auto& fsmap = _fsmap_copy;

  if (prefix == "mds stat") {
    if (f) {
      f->open_object_section("mds_stat");
      dump_info(f.get());
      f->close_section();
      f->flush(ds);
    } else {
      ds << fsmap;
    }
    r = 0;
  } else if (prefix == "mds ok-to-stop") {
    vector<string> ids;
    if (!cmd_getval(cmdmap, "ids", ids)) {
      r = -EINVAL;
      ss << "must specify mds id";
      goto out;
    }
    if (fsmap.is_any_degraded()) {
      ss << "one or more filesystems is currently degraded";
      r = -EBUSY;
      goto out;
    }
    set<mds_gid_t> stopping;
    for (auto& id : ids) {
      ostringstream ess;
      mds_gid_t gid = gid_from_arg(fsmap, id, ess);
      if (gid == MDS_GID_NONE) {
	// the mds doesn't exist, but no file systems are unhappy, so losing it
	// can't have any effect.
	continue;
      }
      stopping.insert(gid);
    }
    set<mds_gid_t> active;
    set<mds_gid_t> standby;
    for (auto gid : stopping) {
      if (fsmap.gid_has_rank(gid)) {
	// ignore standby-replay daemons (at this level)
	if (!fsmap.is_standby_replay(gid)) {
	  auto standby = fsmap.get_standby_replay(gid);
	  if (standby == MDS_GID_NONE ||
	      stopping.count(standby)) {
	    // no standby-replay, or we're also stopping the standby-replay
	    // for this mds
	    active.insert(gid);
	  }
	}
      } else {
	// net loss of a standby
	standby.insert(gid);
      }
    }
    if (fsmap.get_num_standby() - standby.size() < active.size()) {
      r = -EBUSY;
      ss << "insufficent standby MDS daemons to stop active gids "
	 << stringify(active)
	 << " and/or standby gids " << stringify(standby);;
      goto out;
    }
    r = 0;
    ss << "should be safe to stop " << ids;
  } else if (prefix == "fs dump") {
    int64_t epocharg;
    epoch_t epoch;

    const FSMap *fsmapp = &fsmap;
    FSMap dummy;
    if (cmd_getval(cmdmap, "epoch", epocharg)) {
      epoch = epocharg;
      bufferlist b;
      int err = get_version(epoch, b);
      if (err == -ENOENT) {
	r = -ENOENT;
        goto out;
      } else {
	ceph_assert(err == 0);
	ceph_assert(b.length());
	dummy.decode(b);
        fsmapp = &dummy;
      }
    }

    stringstream ds;
    if (f != NULL) {
      f->open_object_section("fsmap");
      fsmapp->dump(f.get());
      f->close_section();
      f->flush(ds);
      r = 0;
    } else {
      fsmapp->print(ds);
      r = 0;
    }

    rdata.append(ds);
    ss << "dumped fsmap epoch " << fsmapp->get_epoch();
  } else if (prefix == "mds metadata") {
    if (!f)
      f.reset(Formatter::create("json-pretty"));

    string who;
    bool all = !cmd_getval(cmdmap, "who", who);
    dout(1) << "all = " << all << dendl;
    if (all) {
      r = 0;
      // Dump all MDSs' metadata
      const auto all_info = fsmap.get_mds_info();

      f->open_array_section("mds_metadata");
      for(const auto &i : all_info) {
        const auto &info = i.second;

        f->open_object_section("mds");
        f->dump_string("name", info.name);
        std::ostringstream get_err;
        r = dump_metadata(fsmap, info.name, f.get(), get_err);
        if (r == -EINVAL || r == -ENOENT) {
          // Drop error, list what metadata we do have
          dout(1) << get_err.str() << dendl;
          r = 0;
        } else if (r != 0) {
          derr << "Unexpected error reading metadata: " << cpp_strerror(r)
               << dendl;
          ss << get_err.str();
          f->close_section();
          break;
        }
        f->close_section();
      }
      f->close_section();
    } else {
      // Dump a single daemon's metadata
      f->open_object_section("mds_metadata");
      r = dump_metadata(fsmap, who, f.get(), ss);
      f->close_section();
    }
    f->flush(ds);
  } else if (prefix == "mds versions") {
    if (!f)
      f.reset(Formatter::create("json-pretty"));
    count_metadata("ceph_version", f.get());
    f->flush(ds);
    r = 0;
  } else if (prefix == "mds count-metadata") {
    if (!f)
      f.reset(Formatter::create("json-pretty"));
    string field;
    cmd_getval(cmdmap, "property", field);
    count_metadata(field, f.get());
    f->flush(ds);
    r = 0;
  } else if (prefix == "fs compat show") {
    string fs_name;
    cmd_getval(cmdmap, "fs_name", fs_name);
    const auto &fs = fsmap.get_filesystem(fs_name);
    if (fs == nullptr) {
      ss << "filesystem '" << fs_name << "' not found";
      r = -ENOENT;
      goto out;
    }

    if (f) {
      f->open_object_section("mds_compat");
      fs->mds_map.compat.dump(f.get());
      f->close_section();
      f->flush(ds);
    } else {
      ds << fs->mds_map.compat;
    }
    r = 0;
  } else if (prefix == "mds compat show") {
      if (f) {
	f->open_object_section("mds_compat");
	fsmap.default_compat.dump(f.get());
	f->close_section();
	f->flush(ds);
      } else {
	ds << fsmap.default_compat;
      }
      r = 0;
  } else if (prefix == "fs get") {
    string fs_name;
    cmd_getval(cmdmap, "fs_name", fs_name);
    const auto &fs = fsmap.get_filesystem(fs_name);
    if (fs == nullptr) {
      ss << "filesystem '" << fs_name << "' not found";
      r = -ENOENT;
    } else {
      if (f != nullptr) {
        f->open_object_section("filesystem");
        fs->dump(f.get());
        f->close_section();
        f->flush(ds);
        r = 0;
      } else {
        fs->print(ds);
        r = 0;
      }
    }
  } else if (prefix == "fs ls") {
    if (f) {
      f->open_array_section("filesystems");
      for (const auto &p : fsmap.filesystems) {
        const auto &fs = p.second;
        f->open_object_section("filesystem");
        {
          const MDSMap &mds_map = fs->mds_map;
          f->dump_string("name", mds_map.fs_name);
          /* Output both the names and IDs of pools, for use by
           * humans and machines respectively */
          f->dump_string("metadata_pool", mon.osdmon()->osdmap.get_pool_name(
                mds_map.metadata_pool));
          f->dump_int("metadata_pool_id", mds_map.metadata_pool);
          f->open_array_section("data_pool_ids");
          for (const auto &id : mds_map.data_pools) {
            f->dump_int("data_pool_id", id);
          }
          f->close_section();

          f->open_array_section("data_pools");
          for (const auto &id : mds_map.data_pools) {
            const auto &name = mon.osdmon()->osdmap.get_pool_name(id);
            f->dump_string("data_pool", name);
          }
          f->close_section();
        }
        f->close_section();
      }
      f->close_section();
      f->flush(ds);
    } else {
      for (const auto &p : fsmap.filesystems) {
        const auto &fs = p.second;
        const MDSMap &mds_map = fs->mds_map;
        const string &md_pool_name = mon.osdmon()->osdmap.get_pool_name(
            mds_map.metadata_pool);
        
        ds << "name: " << mds_map.fs_name << ", metadata pool: "
           << md_pool_name << ", data pools: [";
        for (const auto &id : mds_map.data_pools) {
          const string &pool_name = mon.osdmon()->osdmap.get_pool_name(id);
          ds << pool_name << " ";
        }
        ds << "]" << std::endl;
      }

      if (fsmap.filesystems.empty()) {
        ds << "No filesystems enabled" << std::endl;
      }
    }
    r = 0;
  } else if (prefix == "fs feature ls") {
    if (f) {
      f->open_array_section("cephfs_features");
      for (size_t i = 0; i <= CEPHFS_FEATURE_MAX; ++i) {
	f->open_object_section("feature");
	f->dump_int("index", i);
	f->dump_string("name", cephfs_feature_name(i));
	f->close_section();
      }
      f->close_section();
      f->flush(ds);
    } else {
      for (size_t i = 0; i <= CEPHFS_FEATURE_MAX; ++i) {
        ds << i << " " << cephfs_feature_name(i) << std::endl;
      }
    }
    r = 0;
  } else if (prefix == "fs lsflags") {
    string fs_name;
    cmd_getval(cmdmap, "fs_name", fs_name);
    const auto &fs = fsmap.get_filesystem(fs_name);
    if (!fs) {
      ss << "filesystem '" << fs_name << "' not found";
      r = -ENOENT;
    } else {
      const MDSMap &mds_map = fs->mds_map;
      if (f) {
        mds_map.dump_flags_state(f.get());
        f->flush(ds);
      }
      else {
        mds_map.print_flags(ds);
      }
      r = 0;
    }
  }

out:
  if (r != -1) {
    rdata.append(ds);
    string rs;
    getline(ss, rs);
    mon.reply_command(op, r, rs, rdata, get_last_committed());
    return true;
  } else
    return false;
}

bool MDSMonitor::fail_mds_gid(FSMap &fsmap, mds_gid_t gid)
{
  const auto& info = fsmap.get_info_gid(gid);
  dout(1) << "fail_mds_gid " << gid << " mds." << info.name << " role " << info.rank << dendl;

  ceph_assert(mon.osdmon()->is_writeable());

  epoch_t blocklist_epoch = 0;
  if (info.rank >= 0 && info.state != MDSMap::STATE_STANDBY_REPLAY) {
    utime_t until = ceph_clock_now();
    until += g_conf().get_val<double>("mon_mds_blocklist_interval");
    blocklist_epoch = mon.osdmon()->blocklist(info.addrs, until);
    /* do not delay when we are evicting an MDS */
    force_immediate_propose();
  }

  fsmap.erase(gid, blocklist_epoch);
  last_beacon.erase(gid);
  if (pending_daemon_health.count(gid)) {
    pending_daemon_health.erase(gid);
    pending_daemon_health_rm.insert(gid);
  }

  return blocklist_epoch != 0;
}

mds_gid_t MDSMonitor::gid_from_arg(const FSMap &fsmap, const std::string &arg, std::ostream &ss)
{
  // Try parsing as a role
  mds_role_t role;
  std::ostringstream ignore_err;  // Don't spam 'ss' with parse_role errors
  int r = fsmap.parse_role(arg, &role, ignore_err);
  if (r == 0) {
    // See if a GID is assigned to this role
    const auto &fs = fsmap.get_filesystem(role.fscid);
    ceph_assert(fs != nullptr);  // parse_role ensures it exists
    if (fs->mds_map.is_up(role.rank)) {
      dout(10) << __func__ << ": validated rank/GID " << role
               << " as a rank" << dendl;
      return fs->mds_map.get_mds_info(role.rank).global_id;
    }
  }

  // Try parsing as a gid
  std::string err;
  unsigned long long maybe_gid = strict_strtoll(arg.c_str(), 10, &err);
  if (!err.empty()) {
    // Not a role or a GID, try as a daemon name
    const MDSMap::mds_info_t *mds_info = fsmap.find_by_name(arg);
    if (!mds_info) {
      ss << "MDS named '" << arg
	 << "' does not exist, or is not up";
      return MDS_GID_NONE;
    }
    dout(10) << __func__ << ": resolved MDS name '" << arg
             << "' to GID " << mds_info->global_id << dendl;
    return mds_info->global_id;
  } else {
    // Not a role, but parses as a an integer, might be a GID
    dout(10) << __func__ << ": treating MDS reference '" << arg
	     << "' as an integer " << maybe_gid << dendl;

    if (fsmap.gid_exists(mds_gid_t(maybe_gid))) {
      return mds_gid_t(maybe_gid);
    }
  }

  dout(1) << __func__ << ": rank/GID " << arg
	  << " not a existent rank or GID" << dendl;
  return MDS_GID_NONE;
}

int MDSMonitor::fail_mds(FSMap &fsmap, std::ostream &ss,
    const std::string &arg, MDSMap::mds_info_t *failed_info)
{
  ceph_assert(failed_info != nullptr);

  mds_gid_t gid = gid_from_arg(fsmap, arg, ss);
  if (gid == MDS_GID_NONE) {
    return 0;
  }
  if (!mon.osdmon()->is_writeable()) {
    return -EAGAIN;
  }

  // Take a copy of the info before removing the MDS from the map,
  // so that the caller knows which mds (if any) they ended up removing.
  *failed_info = fsmap.get_info_gid(gid);

  fail_mds_gid(fsmap, gid);
  ss << "failed mds gid " << gid;
  ceph_assert(mon.osdmon()->is_writeable());
  request_proposal(mon.osdmon());
  return 0;
}

bool MDSMonitor::prepare_command(MonOpRequestRef op)
{
  op->mark_mdsmon_event(__func__);
  auto m = op->get_req<MMonCommand>();
  int r = -EINVAL;
  stringstream ss;
  bufferlist rdata;

  cmdmap_t cmdmap;
  if (!cmdmap_from_json(m->cmd, &cmdmap, ss)) {
    string rs = ss.str();
    mon.reply_command(op, -EINVAL, rs, rdata, get_last_committed());
    return false;
  }

  string prefix;
  cmd_getval(cmdmap, "prefix", prefix);

  /* Refuse access if message not associated with a valid session */
  MonSession *session = op->get_session();
  if (!session) {
    mon.reply_command(op, -EACCES, "access denied", rdata, get_last_committed());
    return false;
  }

  auto &pending = get_pending_fsmap_writeable();

  bool batched_propose = false;
  for (const auto &h : handlers) {
    r = h->can_handle(prefix, op, pending, cmdmap, ss);
    if (r == 1) {
      ; // pass, since we got the right handler.
    } else if (r == 0) {
      continue;
    } else {
      goto out;
    }

    batched_propose = h->batched_propose();
    if (batched_propose) {
      paxos.plug();
    }
    r = h->handle(&mon, pending, op, cmdmap, ss);
    if (batched_propose) {
      paxos.unplug();
    }

    if (r == -EAGAIN) {
      // message has been enqueued for retry; return.
      dout(4) << __func__ << " enqueue for retry by prepare_command" << dendl;
      return false;
    } else {
      if (r == 0) {
	// On successful updates, print the updated map
	print_map(pending);
      }
      // Successful or not, we're done: respond.
      goto out;
    }
  }

  r = filesystem_command(pending, op, prefix, cmdmap, ss);
  if (r >= 0) {
    goto out;
  } else if (r == -EAGAIN) {
    // Do not reply, the message has been enqueued for retry
    dout(4) << __func__ << " enqueue for retry by filesystem_command" << dendl;
    return false;
  } else if (r != -ENOSYS) {
    goto out;
  }

  if (r == -ENOSYS && ss.str().empty()) {
    ss << "unrecognized command";
  }

out:
  dout(4) << __func__ << " done, r=" << r << dendl;
  /* Compose response */
  string rs = ss.str();

  if (r >= 0) {
    // success.. delay reply
    wait_for_finished_proposal(op, new Monitor::C_Command(mon, op, r, rs,
					      get_last_committed() + 1));
    if (batched_propose) {
      force_immediate_propose();
    }
    return true;
  } else {
    // reply immediately
    mon.reply_command(op, r, rs, rdata, get_last_committed());
    return false;
  }
}

int MDSMonitor::filesystem_command(
    FSMap &fsmap,
    MonOpRequestRef op,
    std::string const &prefix,
    const cmdmap_t& cmdmap,
    std::stringstream &ss)
{
  dout(4) << __func__ << " prefix='" << prefix << "'" << dendl;
  op->mark_mdsmon_event(__func__);
  int r = 0;
  string whostr;
  cmd_getval(cmdmap, "role", whostr);

  if (prefix == "mds set_state") {
    mds_gid_t gid;
    if (!cmd_getval(cmdmap, "gid", gid)) {
      ss << "error parsing 'gid' value '"
         << cmd_vartype_stringify(cmdmap.at("gid")) << "'";
      return -EINVAL;
    }
    MDSMap::DaemonState state;
    if (!cmd_getval(cmdmap, "state", state)) {
      ss << "error parsing 'state' string value '"
         << cmd_vartype_stringify(cmdmap.at("state")) << "'";
      return -EINVAL;
    }
    if (fsmap.gid_exists(gid, op->get_session()->get_allowed_fs_names())) {
      fsmap.modify_daemon(gid, [state](auto& info) {
        info.state = state;
      });
      ss << "set mds gid " << gid << " to state " << state << " "
         << ceph_mds_state_name(state);
      return 0;
    }
  } else if (prefix == "mds fail") {
    string who;
    cmd_getval(cmdmap, "role_or_gid", who);

    MDSMap::mds_info_t failed_info;
    mds_gid_t gid = gid_from_arg(fsmap, who, ss);
    if (gid == MDS_GID_NONE) {
      ss << "MDS named '" << who << "' does not exist, is not up or you "
	 << "lack the permission to see.";
      return 0;
    }
    if(!fsmap.gid_exists(gid, op->get_session()->get_allowed_fs_names())) {
      ss << "MDS named '" << who << "' does not exist, is not up or you "
	 << "lack the permission to see.";
      return -EINVAL;
    }
    string_view fs_name = fsmap.fs_name_from_gid(gid);
    if (!op->get_session()->fs_name_capable(fs_name, MON_CAP_W)) {
      ss << "Permission denied.";
      return -EPERM;
    }

    r = fail_mds(fsmap, ss, who, &failed_info);
    if (r < 0 && r == -EAGAIN) {
      mon.osdmon()->wait_for_writeable(op, new C_RetryMessage(this, op));
      return -EAGAIN; // don't propose yet; wait for message to be retried
    } else if (r == 0) {
      // Only log if we really did something (not when was already gone)
      if (failed_info.global_id != MDS_GID_NONE) {
        mon.clog->info() << failed_info.human_name() << " marked failed by "
                          << op->get_session()->entity_name;
      }
    }
  } else if (prefix == "mds rm") {
    mds_gid_t gid;
    if (!cmd_getval(cmdmap, "gid", gid)) {
      ss << "error parsing 'gid' value '"
         << cmd_vartype_stringify(cmdmap.at("gid")) << "'";
      return -EINVAL;
    }
    if (!fsmap.gid_exists(gid, op->get_session()->get_allowed_fs_names())) {
      ss << "mds gid " << gid << " does not exist";
      return 0;
    }
    string_view fs_name = fsmap.fs_name_from_gid(gid);
    if (!op->get_session()->fs_name_capable(fs_name, MON_CAP_W)) {
      ss << "Permission denied.";
      return -EPERM;
    }
    const auto &info = fsmap.get_info_gid(gid);
    MDSMap::DaemonState state = info.state;
    if (state > 0) {
    ss << "cannot remove active mds." << info.name
	<< " rank " << info.rank;
    return -EBUSY;
    } else {
    fsmap.erase(gid, {});
    ss << "removed mds gid " << gid;
    return 0;
    }
  } else if (prefix == "mds rmfailed") {
    bool confirm = false;
    cmd_getval(cmdmap, "yes_i_really_mean_it", confirm);
    if (!confirm) {
         ss << "WARNING: this can make your filesystem inaccessible! "
               "Add --yes-i-really-mean-it if you are sure you wish to continue.";
         return -EPERM;
    }
    
    std::string role_str;
    cmd_getval(cmdmap, "role", role_str);
    mds_role_t role;
    const auto fs_names = op->get_session()->get_allowed_fs_names();
    int r = fsmap.parse_role(role_str, &role, ss, fs_names);
    if (r < 0) {
      ss << "invalid role '" << role_str << "'";
      return -EINVAL;
    }
    string_view fs_name = fsmap.get_filesystem(role.fscid)->mds_map.get_fs_name();
    if (!op->get_session()->fs_name_capable(fs_name, MON_CAP_W)) {
      ss << "Permission denied.";
      return -EPERM;
    }

    fsmap.modify_filesystem(
        role.fscid,
        [role](std::shared_ptr<Filesystem> fs)
    {
      fs->mds_map.failed.erase(role.rank);
    });

    ss << "removed failed mds." << role;
    return 0;
    /* TODO: convert to fs commands to update defaults */
  } else if (prefix == "mds compat rm_compat") {
    int64_t f;
    if (!cmd_getval(cmdmap, "feature", f)) {
      ss << "error parsing feature value '"
         << cmd_vartype_stringify(cmdmap.at("feature")) << "'";
      return -EINVAL;
    }
    if (fsmap.default_compat.compat.contains(f)) {
      ss << "removing compat feature " << f;
      fsmap.default_compat.compat.remove(f);
    } else {
      ss << "compat feature " << f << " not present in " << fsmap.default_compat;
    }
    r = 0;
  } else if (prefix == "mds compat rm_incompat") {
    int64_t f;
    if (!cmd_getval(cmdmap, "feature", f)) {
      ss << "error parsing feature value '"
         << cmd_vartype_stringify(cmdmap.at("feature")) << "'";
      return -EINVAL;
    }
    if (fsmap.default_compat.incompat.contains(f)) {
      ss << "removing incompat feature " << f;
      fsmap.default_compat.incompat.remove(f);
    } else {
      ss << "incompat feature " << f << " not present in " << fsmap.default_compat;
    }
    r = 0;
  } else if (prefix == "mds repaired") {
    std::string role_str;
    cmd_getval(cmdmap, "role", role_str);
    mds_role_t role;
    const auto fs_names = op->get_session()->get_allowed_fs_names();
    r = fsmap.parse_role(role_str, &role, ss, fs_names);
    if (r < 0) {
      return r;
    }
    string_view fs_name = fsmap.get_filesystem(role.fscid)->mds_map.get_fs_name();
    if (!op->get_session()->fs_name_capable(fs_name, MON_CAP_W)) {
      ss << "Permission denied.";
      return -EPERM;
    }

    bool modified = fsmap.undamaged(role.fscid, role.rank);
    if (modified) {
      ss << "repaired: restoring rank " << role;
    } else {
      ss << "nothing to do: rank is not damaged";
    }

    r = 0;
  } else if (prefix == "mds freeze") {
    std::string who;
    cmd_getval(cmdmap, "role_or_gid", who);
    mds_gid_t gid = gid_from_arg(fsmap, who, ss);
    if (gid == MDS_GID_NONE) {
      return -EINVAL;
    }

    string_view fs_name = fsmap.fs_name_from_gid(gid);
    if (!op->get_session()->fs_name_capable(fs_name, MON_CAP_W)) {
      ss << "Permission denied.";
      return -EPERM;
    }

    bool freeze = false;
    {
      std::string str;
      cmd_getval(cmdmap, "val", str);
      if ((r = parse_bool(str, &freeze, ss)) != 0) {
        return r;
      }
    }

    auto f = [freeze,gid,&ss](auto& info) {
      if (freeze) {
        ss << "freezing mds." << gid;
        info.freeze();
      } else {
        ss << "unfreezing mds." << gid;
        info.unfreeze();
      }
    };
    fsmap.modify_daemon(gid, f);
    r = 0;
  } else {
    return -ENOSYS;
  }

  return r;
}

void MDSMonitor::check_subs()
{
  // Subscriptions may be to "mdsmap" (MDS and legacy clients),
  // "mdsmap.<namespace>", or to "fsmap" for the full state of all
  // filesystems.  Build a list of all the types we service
  // subscriptions for.

  std::vector<std::string> types = {
    "fsmap",
    "fsmap.user",
    "mdsmap",
  };

  for (const auto &p : get_fsmap().filesystems) {
    const auto &fscid = p.first;
    CachedStackStringStream cos;
    *cos << "mdsmap." << fscid;
    types.push_back(std::string(cos->strv()));
  }

  for (const auto &type : types) {
    auto& subs = mon.session_map.subs;
    auto subs_it = subs.find(type);
    if (subs_it == subs.end())
      continue;
    auto sub_it = subs_it->second->begin();
    while (!sub_it.end()) {
      auto sub = *sub_it;
      ++sub_it; // N.B. check_sub may remove sub!
      check_sub(sub);
    }
  }
}


void MDSMonitor::check_sub(Subscription *sub)
{
  dout(20) << __func__ << ": " << sub->type << dendl;

  // to use const qualifier filter fsmap beforehand
  FSMap _fsmap_copy = get_fsmap();
  _fsmap_copy.filter(sub->session->get_allowed_fs_names());
  const auto& fsmap = _fsmap_copy;
  if (sub->next > fsmap.get_epoch()) {
    return;
  }

  if (sub->type == "fsmap") {
    sub->session->con->send_message(new MFSMap(mon.monmap->fsid, fsmap));
    if (sub->onetime) {
      mon.session_map.remove_sub(sub);
    } else {
      sub->next = fsmap.get_epoch() + 1;
    }
  } else if (sub->type == "fsmap.user") {
    FSMapUser fsmap_u;
    fsmap_u.epoch = fsmap.get_epoch();
    fsmap_u.legacy_client_fscid = fsmap.legacy_client_fscid;
    for (const auto &p : fsmap.filesystems) {
      FSMapUser::fs_info_t& fs_info = fsmap_u.filesystems[p.second->fscid];
      fs_info.cid = p.second->fscid;
      fs_info.name = p.second->mds_map.fs_name;
    }
    sub->session->con->send_message(new MFSMapUser(mon.monmap->fsid, fsmap_u));
    if (sub->onetime) {
      mon.session_map.remove_sub(sub);
    } else {
      sub->next = fsmap.get_epoch() + 1;
    }
  } else if (sub->type.compare(0, 6, "mdsmap") == 0) {
    const bool is_mds = sub->session->name.is_mds();
    mds_gid_t mds_gid = MDS_GID_NONE;
    fs_cluster_id_t fscid = FS_CLUSTER_ID_NONE;
    if (is_mds) {
      // What (if any) namespace are you assigned to?
      auto mds_info = fsmap.get_mds_info();
      for (const auto &p : mds_info) {
        if (p.second.addrs == sub->session->addrs) {
          mds_gid = p.first;
          fscid = fsmap.mds_roles.at(mds_gid);
        }
      }
    } else {
      // You're a client.  Did you request a particular
      // namespace?
      if (sub->type.compare(0, 7, "mdsmap.") == 0) {
        auto namespace_id_str = sub->type.substr(std::string("mdsmap.").size());
        dout(10) << __func__ << ": namespace_id " << namespace_id_str << dendl;
        std::string err;
        fscid = strict_strtoll(namespace_id_str.c_str(), 10, &err);
        if (!err.empty()) {
          // Client asked for a non-existent namespace, send them nothing
          dout(1) << "Invalid client subscription '" << sub->type
                  << "'" << dendl;
          return;
        }
      } else {
        // Unqualified request for "mdsmap": give it the one marked
        // for use by legacy clients.
        if (fsmap.legacy_client_fscid != FS_CLUSTER_ID_NONE) {
          fscid = fsmap.legacy_client_fscid;
        } else {
          dout(1) << "Client subscribed for legacy filesystem but "
                     "none is configured" << dendl;
          return;
        }
      }
      if (!fsmap.filesystem_exists(fscid)) {
        // Client asked for a non-existent namespace, send them nothing
        // TODO: something more graceful for when a client has a filesystem
        // mounted, and the fileysstem is deleted.  Add a "shut down you fool"
        // flag to MMDSMap?
        dout(1) << "Client subscribed to non-existent namespace '" <<
                fscid << "'" << dendl;
        return;
      }
    }
    dout(10) << __func__ << ": is_mds=" << is_mds << ", fscid=" << fscid << dendl;

    // Work out the effective latest epoch
    const MDSMap *mds_map = nullptr;
    MDSMap null_map = MDSMap::create_null_mdsmap();
    if (fscid == FS_CLUSTER_ID_NONE) {
      // For a client, we should have already dropped out
      ceph_assert(is_mds);

      auto it = fsmap.standby_daemons.find(mds_gid);
      if (it != fsmap.standby_daemons.end()) {
        // For an MDS, we need to feed it an MDSMap with its own state in
        null_map.mds_info[mds_gid] = it->second;
        null_map.epoch = fsmap.standby_epochs.at(mds_gid);
      } else {
        null_map.epoch = fsmap.epoch;
      }
      mds_map = &null_map;
    } else {
      // Check the effective epoch 
      mds_map = &fsmap.get_filesystem(fscid)->mds_map;
    }

    ceph_assert(mds_map != nullptr);
    dout(10) << __func__ << " selected MDS map epoch " <<
      mds_map->epoch << " for namespace " << fscid << " for subscriber "
      << sub->session->name << " who wants epoch " << sub->next << dendl;

    if (sub->next > mds_map->epoch) {
      return;
    }
    auto msg = make_message<MMDSMap>(mon.monmap->fsid, *mds_map);

    sub->session->con->send_message(msg.detach());
    if (sub->onetime) {
      mon.session_map.remove_sub(sub);
    } else {
      sub->next = mds_map->get_epoch() + 1;
    }
  }
}


void MDSMonitor::update_metadata(mds_gid_t gid,
				 const map<string, string>& metadata)
{
  dout(20) << __func__ <<  ": mds." << gid << ": " << metadata << dendl;
  if (metadata.empty()) {
    dout(5) << __func__ << ": mds." << gid << ": no metadata!" << dendl;
    return;
  }
  pending_metadata[gid] = metadata;

  MonitorDBStore::TransactionRef t = paxos.get_pending_transaction();
  bufferlist bl;
  encode(pending_metadata, bl);
  t->put(MDS_METADATA_PREFIX, "last_metadata", bl);
}

void MDSMonitor::remove_from_metadata(const FSMap &fsmap, MonitorDBStore::TransactionRef t)
{
  bool update = false;
  for (auto it = pending_metadata.begin(); it != pending_metadata.end(); ) {
    if (!fsmap.gid_exists(it->first)) {
      it = pending_metadata.erase(it);
      update = true;
    } else {
      ++it;
    }
  }
  if (!update)
    return;
  bufferlist bl;
  encode(pending_metadata, bl);
  t->put(MDS_METADATA_PREFIX, "last_metadata", bl);
}

int MDSMonitor::load_metadata(map<mds_gid_t, Metadata>& m)
{
  bufferlist bl;
  int r = mon.store->get(MDS_METADATA_PREFIX, "last_metadata", bl);
  if (r) {
    dout(5) << "Unable to load 'last_metadata'" << dendl;
    return r;
  }

  auto it = bl.cbegin();
  ceph::decode(m, it);
  return 0;
}

void MDSMonitor::count_metadata(const std::string &field, map<string,int> *out)
{
  map<mds_gid_t,Metadata> meta;
  load_metadata(meta);
  for (auto& p : meta) {
    auto q = p.second.find(field);
    if (q == p.second.end()) {
      (*out)["unknown"]++;
    } else {
      (*out)[q->second]++;
    }
  }
}

void MDSMonitor::count_metadata(const std::string &field, Formatter *f)
{
  map<string,int> by_val;
  count_metadata(field, &by_val);
  f->open_object_section(field.c_str());
  for (auto& p : by_val) {
    f->dump_int(p.first.c_str(), p.second);
  }
  f->close_section();
}

void MDSMonitor::get_versions(std::map<string, list<string> > &versions)
{
  map<mds_gid_t,Metadata> meta;
  load_metadata(meta);
  const auto &fsmap = get_fsmap();
  std::map<mds_gid_t, mds_info_t> map = fsmap.get_mds_info();
  dout(10) << __func__ << " mds meta=" << meta << dendl;
  for (auto& p : meta) {
    auto q = p.second.find("ceph_version_short");
    if (q == p.second.end()) continue;
    versions[q->second].push_back(string("mds.") + map[p.first].name);
  }
}

int MDSMonitor::dump_metadata(const FSMap& fsmap, const std::string &who,
    Formatter *f, ostream& err)
{
  ceph_assert(f);

  mds_gid_t gid = gid_from_arg(fsmap, who, err);
  if (gid == MDS_GID_NONE) {
    return -EINVAL;
  }

  map<mds_gid_t, Metadata> metadata;
  if (int r = load_metadata(metadata)) {
    err << "Unable to load 'last_metadata'";
    return r;
  }

  if (!metadata.count(gid)) {
    return -ENOENT;
  }
  const Metadata& m = metadata[gid];
  for (Metadata::const_iterator p = m.begin(); p != m.end(); ++p) {
    f->dump_string(p->first.c_str(), p->second);
  }
  return 0;
}

int MDSMonitor::print_nodes(Formatter *f)
{
  ceph_assert(f);

  const auto &fsmap = get_fsmap();

  map<mds_gid_t, Metadata> metadata;
  if (int r = load_metadata(metadata)) {
    return r;
  }

  map<string, list<string> > mdses; // hostname => mds
  for (const auto &p : metadata) {
    const mds_gid_t& gid = p.first;
    const Metadata& m = p.second;
    Metadata::const_iterator hostname = m.find("hostname");
    if (hostname == m.end()) {
      // not likely though
      continue;
    }
    if (!fsmap.gid_exists(gid)) {
      dout(5) << __func__ << ": GID " << gid << " not existent" << dendl;
      continue;
    }
    const MDSMap::mds_info_t& mds_info = fsmap.get_info_gid(gid);
    mdses[hostname->second].push_back(mds_info.name);
  }

  dump_services(f, mdses, "mds");
  return 0;
}

/**
 * If a cluster is undersized (with respect to max_mds), then
 * attempt to find daemons to grow it. If the cluster is oversized
 * (with respect to max_mds) then shrink it by stopping its highest rank.
 */
bool MDSMonitor::maybe_resize_cluster(FSMap &fsmap, fs_cluster_id_t fscid)
{
  auto&& fs = fsmap.get_filesystem(fscid);
  auto &mds_map = fs->mds_map;

  int in = mds_map.get_num_in_mds();
  int max = mds_map.get_max_mds();

  dout(20) << __func__ << " in " << in << " max " << max << dendl;

  /* Check that both the current epoch mds_map is resizeable as well as the
   * current batch of changes in pending. This is important if an MDS is
   * becoming active in the next epoch.
   */
  if (!get_fsmap().filesystem_exists(fscid) ||
      !get_fsmap().get_filesystem(fscid)->mds_map.is_resizeable() ||
      !mds_map.is_resizeable()) {
    dout(5) << __func__ << " mds_map is not currently resizeable" << dendl;
    return false;
  }

  if (in < max && !mds_map.test_flag(CEPH_MDSMAP_NOT_JOINABLE)) {
    mds_rank_t mds = mds_rank_t(0);
    while (mds_map.is_in(mds)) {
      mds++;
    }
    auto info = fsmap.find_replacement_for({fscid, mds});
    if (!info) {
      return false;
    }

    dout(1) << "assigned standby " << info->addrs
            << " as mds." << mds << dendl;
    mon.clog->info() << info->human_name() << " assigned to "
                         "filesystem " << mds_map.fs_name << " as rank "
                      << mds << " (now has " << mds_map.get_num_in_mds() + 1
                      << " ranks)";
    fsmap.promote(info->global_id, *fs, mds);
    return true;
  } else if (in > max) {
    mds_rank_t target = in - 1;
    const auto &info = mds_map.get_info(target);
    if (mds_map.is_active(target)) {
      dout(1) << "stopping " << target << dendl;
      mon.clog->info() << "stopping " << info.human_name();
      auto f = [](auto& info) {
        info.state = MDSMap::STATE_STOPPING;
      };
      fsmap.modify_daemon(info.global_id, f);
      return true;
    } else {
      dout(20) << "skipping stop of " << target << dendl;
      return false;
    }
  }

  return false;
}


/**
 * Fail a daemon and replace it with a suitable standby.
 */
bool MDSMonitor::drop_mds(FSMap &fsmap, mds_gid_t gid, const mds_info_t* rep_info, bool *osd_propose)
{
  ceph_assert(osd_propose != nullptr);

  const auto fscid = fsmap.mds_roles.at(gid);
  const auto& info = fsmap.get_info_gid(gid);
  const auto rank = info.rank;
  const auto state = info.state;

  if (info.is_frozen()) {
    return false;
  } else if (state == MDSMap::STATE_STANDBY_REPLAY ||
             state == MDSMap::STATE_STANDBY) {
    dout(1)  << " failing and removing standby " << gid << " " << info.addrs
	     << " mds." << rank
	     << "." << info.inc << " " << ceph_mds_state_name(state)
	     << dendl;
    *osd_propose |= fail_mds_gid(fsmap, gid);
    return true;
  } else if (rank >= 0 && rep_info) {
    auto fs = fsmap.filesystems.at(fscid);
    if (fs->mds_map.test_flag(CEPH_MDSMAP_NOT_JOINABLE)) {
      return false;
    }
    // are we in?
    // and is there a non-laggy standby that can take over for us?
    dout(1)  << " replacing " << gid << " " << info.addrs
	     << " mds." << rank << "." << info.inc
	     << " " << ceph_mds_state_name(state)
	     << " with " << rep_info->global_id << "/" << rep_info->name << " " << rep_info->addrs
	     << dendl;

    mon.clog->warn() << "Replacing " << info.human_name()
                      << " as rank " << rank
                      << " with standby " << rep_info->human_name();

    // Remove the old one
    *osd_propose |= fail_mds_gid(fsmap, gid);

    // Promote the replacement
    fsmap.promote(rep_info->global_id, *fs, rank);

    return true;
  }
  return false;
}

bool MDSMonitor::check_health(FSMap& fsmap, bool* propose_osdmap)
{
  bool do_propose = false;
  const auto now = mono_clock::now();
  const bool osdmap_writeable = mon.osdmon()->is_writeable();
  const auto mds_beacon_grace = g_conf().get_val<double>("mds_beacon_grace");
  const auto mds_beacon_interval = g_conf().get_val<double>("mds_beacon_interval");

  if (mono_clock::is_zero(last_tick)) {
    last_tick = now;
  }

  {
    auto since_last = std::chrono::duration<double>(now-last_tick);

    if (since_last.count() > (mds_beacon_grace-mds_beacon_interval)) {
      // This case handles either local slowness (calls being delayed
      // for whatever reason) or cluster election slowness (a long gap
      // between calls while an election happened)
      dout(1) << __func__ << ": resetting beacon timeouts due to mon delay "
              "(slow election?) of " << since_last.count() << " seconds" << dendl;
      for (auto& p : last_beacon) {
        p.second.stamp = now;
      }
    }
  }

  // make sure last_beacon is fully populated
  for (auto& p : fsmap.mds_roles) {
    auto& gid = p.first;
    last_beacon.emplace(std::piecewise_construct,
        std::forward_as_tuple(gid),
        std::forward_as_tuple(now, 0));
  }

  // We will only take decisive action (replacing/removing a daemon)
  // if we have some indication that some other daemon(s) are successfully
  // getting beacons through recently.
  mono_time latest_beacon = mono_clock::zero();
  for (const auto& p : last_beacon) {
    latest_beacon = std::max(p.second.stamp, latest_beacon);
  }
  auto since = std::chrono::duration<double>(now-latest_beacon);
  const bool may_replace = since.count() <
      std::max(g_conf()->mds_beacon_interval, g_conf()->mds_beacon_grace * 0.5);

  // check beacon timestamps
  std::vector<mds_gid_t> to_remove;
  const bool mon_down = mon.is_mon_down();
  const auto mds_beacon_mon_down_grace =
      g_conf().get_val<std::chrono::seconds>("mds_beacon_mon_down_grace");
  const auto quorum_age = std::chrono::seconds(mon.quorum_age());
  const bool new_quorum = quorum_age < mds_beacon_mon_down_grace;
  for (auto it = last_beacon.begin(); it != last_beacon.end(); ) {
    auto& [gid, beacon_info] = *it;
    auto since_last = std::chrono::duration<double>(now-beacon_info.stamp);

    if (!fsmap.gid_exists(gid)) {
      // gid no longer exists, remove from tracked beacons
      it = last_beacon.erase(it);
      continue;
    }

    if (since_last.count() >= g_conf()->mds_beacon_grace) {
      auto& info = fsmap.get_info_gid(gid);
      dout(1) << "no beacon from mds." << info.rank << "." << info.inc
              << " (gid: " << gid << " addr: " << info.addrs
              << " state: " << ceph_mds_state_name(info.state) << ")"
              << " since " << since_last.count() << dendl;
      if ((mon_down || new_quorum) && since_last < mds_beacon_mon_down_grace) {
        /* The MDS may be sending beacons to a monitor not yet in quorum or
         * temporarily partitioned. Hold off on removal for a little longer...
         */
        dout(10) << "deferring removal for mds_beacon_mon_down_grace during MON_DOWN" << dendl;
        ++it;
        continue;
      }
      // If the OSDMap is writeable, we can blocklist things, so we can
      // try failing any laggy MDS daemons.  Consider each one for failure.
      if (!info.laggy()) {
        dout(1)  << " marking " << gid << " " << info.addrs
	         << " mds." << info.rank << "." << info.inc
	         << " " << ceph_mds_state_name(info.state)
	         << " laggy" << dendl;
        fsmap.modify_daemon(info.global_id, [](auto& info) {
            info.laggy_since = ceph_clock_now();
        });
        do_propose = true;
      }
      if (osdmap_writeable && may_replace) {
        to_remove.push_back(gid); // drop_mds may invalidate iterator
      }
    }

    ++it;
  }

  for (const auto& gid : to_remove) {
    auto info = fsmap.get_info_gid(gid);
    const mds_info_t* rep_info = nullptr;
    if (info.rank >= 0) {
      auto fscid = fsmap.fscid_from_gid(gid);
      rep_info = fsmap.find_replacement_for({fscid, info.rank});
    }
    bool dropped = drop_mds(fsmap, gid, rep_info, propose_osdmap);
    if (dropped) {
      mon.clog->info() << "MDS " << info.human_name()
                        << " is removed because it is dead or otherwise unavailable.";
      do_propose = true;
    }
  }

  if (osdmap_writeable) {
    for (auto& [fscid, fs] : fsmap.filesystems) {
      if (!fs->mds_map.test_flag(CEPH_MDSMAP_NOT_JOINABLE) &&
          fs->mds_map.is_resizeable()) {
        // Check if a rank or standby-replay should be replaced with a stronger
        // affinity standby. This looks at ranks and standby-replay:
        for (const auto& [gid, info] : fs->mds_map.get_mds_info()) {
          const auto join_fscid = info.join_fscid;
          if (join_fscid == fscid)
            continue;
          const auto rank = info.rank;
          const auto state = info.state;
          const mds_info_t* rep_info = nullptr;
          if (state == MDSMap::STATE_STANDBY_REPLAY) {
            rep_info = fsmap.get_available_standby(*fs);
          } else if (state == MDSMap::STATE_ACTIVE) {
            rep_info = fsmap.find_replacement_for({fscid, rank});
          } else {
            /* N.B. !is_degraded() */
            ceph_abort_msg("invalid state in MDSMap");
          }
          if (!rep_info) {
            break;
          }
          bool better_affinity = false;
          if (join_fscid == FS_CLUSTER_ID_NONE) {
            better_affinity = (rep_info->join_fscid == fscid);
          } else {
            better_affinity = (rep_info->join_fscid == fscid) ||
                              (rep_info->join_fscid == FS_CLUSTER_ID_NONE);
          }
          if (better_affinity) {
            if (state == MDSMap::STATE_STANDBY_REPLAY) {
              mon.clog->info() << "Dropping low affinity standby-replay "
                                << info.human_name()
                                << " in favor of higher affinity standby.";
              *propose_osdmap |= fail_mds_gid(fsmap, gid);
              /* Now let maybe_promote_standby do the promotion. */
            } else {
              mon.clog->info() << "Dropping low affinity active "
                                << info.human_name()
                                << " in favor of higher affinity standby.";
              do_propose |= drop_mds(fsmap, gid, rep_info, propose_osdmap);
            }
            break; /* don't replace more than one per tick per fs */
          }
        }
      }
    }
  }
  return do_propose;
}

bool MDSMonitor::maybe_promote_standby(FSMap &fsmap, Filesystem& fs)
{
  if (fs.mds_map.test_flag(CEPH_MDSMAP_NOT_JOINABLE)) {
    return false;
  }

  bool do_propose = false;

  // have a standby take over?
  set<mds_rank_t> failed;
  fs.mds_map.get_failed_mds_set(failed);
  for (const auto& rank : failed) {
    auto info = fsmap.find_replacement_for({fs.fscid, rank});
    if (info) {
      dout(1) << " taking over failed mds." << rank << " with " << info->global_id
              << "/" << info->name << " " << info->addrs << dendl;
      mon.clog->info() << "Standby " << info->human_name()
                        << " assigned to filesystem " << fs.mds_map.fs_name
                        << " as rank " << rank;

      fsmap.promote(info->global_id, fs, rank);
      do_propose = true;
    }
  }

  if (fs.mds_map.is_resizeable() && fs.mds_map.allows_standby_replay()) {
    // There were no failures to replace, so try using any available standbys
    // as standby-replay daemons. Don't do this when the cluster is degraded
    // as a standby-replay daemon may try to read a journal being migrated.
    for (;;) {
      auto info = fsmap.get_available_standby(fs);
      if (!info) break;
      dout(20) << "standby available mds." << info->global_id << dendl;
      bool changed = false;
      for (const auto& rank : fs.mds_map.in) {
        dout(20) << "examining " << rank << dendl;
        if (fs.mds_map.is_followable(rank)) {
          dout(1) << "  setting mds." << info->global_id
                  << " to follow mds rank " << rank << dendl;
          fsmap.assign_standby_replay(info->global_id, fs.fscid, rank);
          do_propose = true;
          changed = true;
          break;
        }
      }
      if (!changed) break;
    }
  }

  return do_propose;
}

void MDSMonitor::tick()
{
  if (!is_active() || !is_leader()) return;

  auto &pending = get_pending_fsmap_writeable();

  bool do_propose = false;
  bool propose_osdmap = false;

  if (check_fsmap_struct_version) {
    /* Allow time for trimming otherwise PaxosService::is_writeable will always
     * be false.
     */

    auto now = clock::now();
    auto elapsed = now - last_fsmap_struct_flush;
    if (elapsed > std::chrono::seconds(30)) {
      FSMap fsmap;
      bufferlist bl;
      auto v = get_first_committed();
      int err = get_version(v, bl);
      if (err) {
        derr << "could not get version " << v << dendl;
        ceph_abort();
      }
      try {
        fsmap.decode(bl);
      } catch (const ceph::buffer::malformed_input& e) {
        dout(5) << "flushing old fsmap struct because unable to decode FSMap: " << e.what() << dendl;
      }
      /* N.B. FSMap::is_struct_old is also true for undecoded (failed to decode) FSMap */
      if (fsmap.is_struct_old()) {
        dout(5) << "fsmap struct is too old; proposing to flush out old versions" << dendl;
        do_propose = true;
        last_fsmap_struct_flush = now;
      } else {
        dout(20) << "struct is recent" << dendl;
        check_fsmap_struct_version = false;
      }
    }
  }

  do_propose |= pending.check_health();

  /* Check health and affinity of ranks */
  do_propose |= check_health(pending, &propose_osdmap);

  /* Resize the cluster according to max_mds. */
  for (auto& p : pending.filesystems) {
    do_propose |= maybe_resize_cluster(pending, p.second->fscid);
  }

  /* Replace any failed ranks. */
  for (auto& p : pending.filesystems) {
    do_propose |= maybe_promote_standby(pending, *p.second);
  }

  if (propose_osdmap) {
    request_proposal(mon.osdmon());
  }

  if (do_propose) {
    propose_pending();
  }

  last_tick = mono_clock::now();
}

MDSMonitor::MDSMonitor(Monitor &mn, Paxos &p, string service_name)
  : PaxosService(mn, p, service_name)
{
  handlers = FileSystemCommandHandler::load(&p);
}

void MDSMonitor::on_restart()
{
  // Clear out the leader-specific state.
  last_tick = mono_clock::now();
  last_beacon.clear();
}