update ceph source to reef 18.1.2

[ceph.git] / ceph / src / blk / kernel / KernelDevice.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) 2014 Red Hat
 *
 * This is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License version 2.1, as published by the Free Software
 * Foundation.  See file COPYING.
 *
 */

#include <limits>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/file.h>
#include <sys/mman.h>

#include <boost/container/flat_map.hpp>
#include <boost/lockfree/queue.hpp>

#include "KernelDevice.h"
#include "include/buffer_raw.h"
#include "include/intarith.h"
#include "include/types.h"
#include "include/compat.h"
#include "include/stringify.h"
#include "include/str_map.h"
#include "common/blkdev.h"
#include "common/buffer_instrumentation.h"
#include "common/errno.h"
#if defined(__FreeBSD__)
#include "bsm/audit_errno.h"
#endif
#include "common/debug.h"
#include "common/numa.h"

#include "global/global_context.h"
#include "io_uring.h"

#define dout_context cct
#define dout_subsys ceph_subsys_bdev
#undef dout_prefix
#define dout_prefix *_dout << "bdev(" << this << " " << path << ") "

using std::list;
using std::map;
using std::string;
using std::vector;

using ceph::bufferlist;
using ceph::bufferptr;
using ceph::make_timespan;
using ceph::mono_clock;
using ceph::operator <<;

KernelDevice::KernelDevice(CephContext* cct, aio_callback_t cb, void *cbpriv, aio_callback_t d_cb, void *d_cbpriv)
  : BlockDevice(cct, cb, cbpriv),
    aio(false), dio(false),
    discard_callback(d_cb),
    discard_callback_priv(d_cbpriv),
    aio_stop(false),
    discard_started(false),
    discard_stop(false),
    aio_thread(this),
    discard_thread(this),
    injecting_crash(0)
{
  fd_directs.resize(WRITE_LIFE_MAX, -1);
  fd_buffereds.resize(WRITE_LIFE_MAX, -1);

  bool use_ioring = cct->_conf.get_val<bool>("bdev_ioring");
  unsigned int iodepth = cct->_conf->bdev_aio_max_queue_depth;

  if (use_ioring && ioring_queue_t::supported()) {
    bool use_ioring_hipri = cct->_conf.get_val<bool>("bdev_ioring_hipri");
    bool use_ioring_sqthread_poll = cct->_conf.get_val<bool>("bdev_ioring_sqthread_poll");
    io_queue = std::make_unique<ioring_queue_t>(iodepth, use_ioring_hipri, use_ioring_sqthread_poll);
  } else {
    static bool once;
    if (use_ioring && !once) {
      derr << "WARNING: io_uring API is not supported! Fallback to libaio!"
           << dendl;
      once = true;
    }
    io_queue = std::make_unique<aio_queue_t>(iodepth);
  }
}

int KernelDevice::_lock()
{
  // When the block changes, systemd-udevd will open the block,
  // read some information and close it. Then a failure occurs here.
  // So we need to try again here.
  int fd = fd_directs[WRITE_LIFE_NOT_SET];
  dout(10) << __func__ << " fd=" << fd << dendl;
  uint64_t nr_tries = 0;
  for (;;) {
    struct flock fl = { .l_type = F_WRLCK,
                        .l_whence = SEEK_SET };
    int r = ::fcntl(fd, F_OFD_SETLK, &fl);
    if (r < 0) {
      if (errno == EINVAL) {
        r = ::flock(fd, LOCK_EX | LOCK_NB);
      }
    }
    if (r == 0) {
      return 0;
    }
    if (errno != EAGAIN) {
      return -errno;
    }
    dout(1) << __func__ << " flock busy on " << path << dendl;
    if (const uint64_t max_retry =
        cct->_conf.get_val<uint64_t>("bdev_flock_retry");
        max_retry > 0 && nr_tries++ == max_retry) {
      return -EAGAIN;
    }
    double retry_interval =
      cct->_conf.get_val<double>("bdev_flock_retry_interval");
    std::this_thread::sleep_for(ceph::make_timespan(retry_interval));
  }
}

int KernelDevice::open(const string& p)
{
  path = p;
  int r = 0, i = 0;
  dout(1) << __func__ << " path " << path << dendl;

  struct stat statbuf;
  bool is_block;
  r = stat(path.c_str(), &statbuf);
  if (r != 0) {
    derr << __func__ << " stat got: " << cpp_strerror(r) << dendl;
    goto out_fail;
  }
  is_block = (statbuf.st_mode & S_IFMT) == S_IFBLK;
  for (i = 0; i < WRITE_LIFE_MAX; i++) {
    int flags = 0;
    if (lock_exclusive && is_block && (i == 0)) {
      // If opening block device use O_EXCL flag. It gives us best protection,
      // as no other process can overwrite the data for as long as we are running.
      // For block devices ::flock is not enough,
      // since 2 different inodes with same major/minor can be locked.
      // Exclusion by O_EXCL works in containers too.
      flags |= O_EXCL;
    }
    int fd = ::open(path.c_str(), O_RDWR | O_DIRECT | flags);
    if (fd  < 0) {
      r = -errno;
      break;
    }
    fd_directs[i] = fd;

    fd  = ::open(path.c_str(), O_RDWR | O_CLOEXEC);
    if (fd  < 0) {
      r = -errno;
      break;
    }
    fd_buffereds[i] = fd;
  }

  if (i != WRITE_LIFE_MAX) {
    derr << __func__ << " open got: " << cpp_strerror(r) << dendl;
    goto out_fail;
  }

#if defined(F_SET_FILE_RW_HINT)
  for (i = WRITE_LIFE_NONE; i < WRITE_LIFE_MAX; i++) {
    if (fcntl(fd_directs[i], F_SET_FILE_RW_HINT, &i) < 0) {
      r = -errno;
      break;
    }
    if (fcntl(fd_buffereds[i], F_SET_FILE_RW_HINT, &i) < 0) {
      r = -errno;
      break;
    }
  }
  if (i != WRITE_LIFE_MAX) {
    enable_wrt = false;
    dout(0) << "ioctl(F_SET_FILE_RW_HINT) on " << path << " failed: " << cpp_strerror(r) << dendl;
  }
#endif

  dio = true;
  aio = cct->_conf->bdev_aio;
  if (!aio) {
    ceph_abort_msg("non-aio not supported");
  }

  // disable readahead as it will wreak havoc on our mix of
  // directio/aio and buffered io.
  r = posix_fadvise(fd_buffereds[WRITE_LIFE_NOT_SET], 0, 0, POSIX_FADV_RANDOM);
  if (r) {
    r = -r;
    derr << __func__ << " posix_fadvise got: " << cpp_strerror(r) << dendl;
    goto out_fail;
  }

  if (lock_exclusive) {
    // We need to keep soft locking (via flock()) because O_EXCL does not work for regular files.
    // This is as good as we can get. Other processes can still overwrite the data,
    // but at least we are protected from mounting same device twice in ceph processes.
    // We also apply soft locking for block devices, as it populates /proc/locks. (see lslocks)
    r = _lock();
    if (r < 0) {
      derr << __func__ << " failed to lock " << path << ": " << cpp_strerror(r)
           << dendl;
      goto out_fail;
    }
  }

  struct stat st;
  r = ::fstat(fd_directs[WRITE_LIFE_NOT_SET], &st);
  if (r < 0) {
    r = -errno;
    derr << __func__ << " fstat got " << cpp_strerror(r) << dendl;
    goto out_fail;
  }

  // Operate as though the block size is 4 KB.  The backing file
  // blksize doesn't strictly matter except that some file systems may
  // require a read/modify/write if we write something smaller than
  // it.
  block_size = cct->_conf->bdev_block_size;
  if (block_size != (unsigned)st.st_blksize) {
    dout(1) << __func__ << " backing device/file reports st_blksize "
            << st.st_blksize << ", using bdev_block_size "
            << block_size << " anyway" << dendl;
  }


  {
    BlkDev blkdev_direct(fd_directs[WRITE_LIFE_NOT_SET]);
    BlkDev blkdev_buffered(fd_buffereds[WRITE_LIFE_NOT_SET]);

    if (S_ISBLK(st.st_mode)) {
      int64_t s;
      r = blkdev_direct.get_size(&s);
      if (r < 0) {
        goto out_fail;
      }
      size = s;
    } else {
      size = st.st_size;
    }

    char partition[PATH_MAX], devname[PATH_MAX];
    if ((r = blkdev_buffered.partition(partition, PATH_MAX)) ||
        (r = blkdev_buffered.wholedisk(devname, PATH_MAX))) {
      derr << "unable to get device name for " << path << ": "
        << cpp_strerror(r) << dendl;
      rotational = true;
    } else {
      dout(20) << __func__ << " devname " << devname << dendl;
      rotational = blkdev_buffered.is_rotational();
      support_discard = blkdev_buffered.support_discard();
      optimal_io_size = blkdev_buffered.get_optimal_io_size();
      this->devname = devname;
      // check if any extended block device plugin recognizes this device
      // detect_vdo has moved into the VDO plugin
      int rc = extblkdev::detect_device(cct, devname, ebd_impl);
      if (rc != 0) {
        dout(20) << __func__ << " no plugin volume maps to " << devname << dendl;
      }
    }
  }

  r = _post_open();
  if (r < 0) {
    goto out_fail;
  }

  r = _aio_start();
  if (r < 0) {
    goto out_fail;
  }
  if (support_discard && cct->_conf->bdev_enable_discard && cct->_conf->bdev_async_discard) {
    _discard_start();
  }

  // round size down to an even block
  size &= ~(block_size - 1);

  dout(1) << __func__
          << " size " << size
          << " (0x" << std::hex << size << std::dec << ", "
          << byte_u_t(size) << ")"
          << " block_size " << block_size
          << " (" << byte_u_t(block_size) << ")"
          << " " << (rotational ? "rotational device," : "non-rotational device,")
      << " discard " << (support_discard ? "supported" : "not supported")
          << dendl;
  return 0;

out_fail:
  for (i = 0; i < WRITE_LIFE_MAX; i++) {
    if (fd_directs[i] >= 0) {
      VOID_TEMP_FAILURE_RETRY(::close(fd_directs[i]));
      fd_directs[i] = -1;
    } else {
      break;
    }
    if (fd_buffereds[i] >= 0) {
      VOID_TEMP_FAILURE_RETRY(::close(fd_buffereds[i]));
      fd_buffereds[i] = -1;
    } else {
      break;
    }
  }
  return r;
}

int KernelDevice::get_devices(std::set<std::string> *ls) const
{
  if (devname.empty()) {
    return 0;
  }
  get_raw_devices(devname, ls);
  return 0;
}

void KernelDevice::close()
{
  dout(1) << __func__ << dendl;
  _aio_stop();
  if (discard_thread.is_started()) {
    _discard_stop();
  }
  _pre_close();

  extblkdev::release_device(ebd_impl);

  for (int i = 0; i < WRITE_LIFE_MAX; i++) {
    assert(fd_directs[i] >= 0);
    VOID_TEMP_FAILURE_RETRY(::close(fd_directs[i]));
    fd_directs[i] = -1;

    assert(fd_buffereds[i] >= 0);
    VOID_TEMP_FAILURE_RETRY(::close(fd_buffereds[i]));
    fd_buffereds[i] = -1;
  }
  path.clear();
}

int KernelDevice::collect_metadata(const string& prefix, map<string,string> *pm) const
{
  (*pm)[prefix + "support_discard"] = stringify((int)(bool)support_discard);
  (*pm)[prefix + "rotational"] = stringify((int)(bool)rotational);
  (*pm)[prefix + "size"] = stringify(get_size());
  (*pm)[prefix + "block_size"] = stringify(get_block_size());
  (*pm)[prefix + "optimal_io_size"] = stringify(get_optimal_io_size());
  (*pm)[prefix + "driver"] = "KernelDevice";
  if (rotational) {
    (*pm)[prefix + "type"] = "hdd";
  } else {
    (*pm)[prefix + "type"] = "ssd";
  }
  // if compression device detected, collect meta data for device
  // VDO specific meta data has moved into VDO plugin
  if (ebd_impl) {
    ebd_impl->collect_metadata(prefix, pm);
  }

  {
    string res_names;
    std::set<std::string> devnames;
    if (get_devices(&devnames) == 0) {
      for (auto& dev : devnames) {
        if (!res_names.empty()) {
          res_names += ",";
        }
        res_names += dev;
      }
      if (res_names.size()) {
        (*pm)[prefix + "devices"] = res_names;
      }
    }
  }

  struct stat st;
  int r = ::fstat(fd_buffereds[WRITE_LIFE_NOT_SET], &st);
  if (r < 0)
    return -errno;
  if (S_ISBLK(st.st_mode)) {
    (*pm)[prefix + "access_mode"] = "blk";

    char buffer[1024] = {0};
    BlkDev blkdev{fd_buffereds[WRITE_LIFE_NOT_SET]};
    if (r = blkdev.partition(buffer, sizeof(buffer)); r) {
      (*pm)[prefix + "partition_path"] = "unknown";
    } else {
      (*pm)[prefix + "partition_path"] = buffer;
    }
    buffer[0] = '\0';
    if (r = blkdev.partition(buffer, sizeof(buffer)); r) {
      (*pm)[prefix + "dev_node"] = "unknown";
    } else {
      (*pm)[prefix + "dev_node"] = buffer;
    }
    if (!r) {
      return 0;
    }
    buffer[0] = '\0';
    blkdev.model(buffer, sizeof(buffer));
    (*pm)[prefix + "model"] = buffer;

    buffer[0] = '\0';
    blkdev.dev(buffer, sizeof(buffer));
    (*pm)[prefix + "dev"] = buffer;

    // nvme exposes a serial number
    buffer[0] = '\0';
    blkdev.serial(buffer, sizeof(buffer));
    (*pm)[prefix + "serial"] = buffer;

    // numa
    int node;
    r = blkdev.get_numa_node(&node);
    if (r >= 0) {
      (*pm)[prefix + "numa_node"] = stringify(node);
    }
  } else {
    (*pm)[prefix + "access_mode"] = "file";
    (*pm)[prefix + "path"] = path;
  }
  return 0;
}

int KernelDevice::get_ebd_state(ExtBlkDevState &state) const
{
  // use compression driver plugin to determine physical size and availability
  // VDO specific get_thin_utilization has moved into VDO plugin
  if (ebd_impl) {
    return ebd_impl->get_state(state);
  }
  return -ENOENT;
}

int KernelDevice::choose_fd(bool buffered, int write_hint) const
{
#if defined(F_SET_FILE_RW_HINT)
  if (!enable_wrt)
    write_hint = WRITE_LIFE_NOT_SET;
#else
  // Without WRITE_LIFE capabilities, only one file is used.
  // And rocksdb sets this value also to > 0, so we need to catch this here
  // instead of trusting rocksdb to set write_hint.
  write_hint = WRITE_LIFE_NOT_SET;
#endif
  return buffered ? fd_buffereds[write_hint] : fd_directs[write_hint];
}

int KernelDevice::flush()
{
  // protect flush with a mutex.  note that we are not really protecting
  // data here.  instead, we're ensuring that if any flush() caller
  // sees that io_since_flush is true, they block any racing callers
  // until the flush is observed.  that allows racing threads to be
  // calling flush while still ensuring that *any* of them that got an
  // aio completion notification will not return before that aio is
  // stable on disk: whichever thread sees the flag first will block
  // followers until the aio is stable.
  std::lock_guard l(flush_mutex);

  bool expect = true;
  if (!io_since_flush.compare_exchange_strong(expect, false)) {
    dout(10) << __func__ << " no-op (no ios since last flush), flag is "
             << (int)io_since_flush.load() << dendl;
    return 0;
  }

  dout(10) << __func__ << " start" << dendl;
  if (cct->_conf->bdev_inject_crash) {
    ++injecting_crash;
    // sleep for a moment to give other threads a chance to submit or
    // wait on io that races with a flush.
    derr << __func__ << " injecting crash. first we sleep..." << dendl;
    sleep(cct->_conf->bdev_inject_crash_flush_delay);
    derr << __func__ << " and now we die" << dendl;
    cct->_log->flush();
    _exit(1);
  }
  utime_t start = ceph_clock_now();
  int r = ::fdatasync(fd_directs[WRITE_LIFE_NOT_SET]);
  utime_t end = ceph_clock_now();
  utime_t dur = end - start;
  if (r < 0) {
    r = -errno;
    derr << __func__ << " fdatasync got: " << cpp_strerror(r) << dendl;
    ceph_abort();
  }
  dout(5) << __func__ << " in " << dur << dendl;;
  return r;
}

int KernelDevice::_aio_start()
{
  if (aio) {
    dout(10) << __func__ << dendl;
    int r = io_queue->init(fd_directs);
    if (r < 0) {
      if (r == -EAGAIN) {
        derr << __func__ << " io_setup(2) failed with EAGAIN; "
             << "try increasing /proc/sys/fs/aio-max-nr" << dendl;
      } else {
        derr << __func__ << " io_setup(2) failed: " << cpp_strerror(r) << dendl;
      }
      return r;
    }
    aio_thread.create("bstore_aio");
  }
  return 0;
}

void KernelDevice::_aio_stop()
{
  if (aio) {
    dout(10) << __func__ << dendl;
    aio_stop = true;
    aio_thread.join();
    aio_stop = false;
    io_queue->shutdown();
  }
}

void KernelDevice::_discard_start()
{
    discard_thread.create("bstore_discard");
}

void KernelDevice::_discard_stop()
{
  dout(10) << __func__ << dendl;
  {
    std::unique_lock l(discard_lock);
    while (!discard_started) {
      discard_cond.wait(l);
    }
    discard_stop = true;
    discard_cond.notify_all();
  }
  discard_thread.join();
  {
    std::lock_guard l(discard_lock);
    discard_stop = false;
  }
  dout(10) << __func__ << " stopped" << dendl;
}

void KernelDevice::discard_drain()
{
  dout(10) << __func__ << dendl;
  std::unique_lock l(discard_lock);
  while (!discard_queued.empty() || discard_running) {
    discard_cond.wait(l);
  }
}

static bool is_expected_ioerr(const int r)
{
  // https://lxr.missinglinkelectronics.com/linux+v4.15/block/blk-core.c#L135
  return (r == -EOPNOTSUPP || r == -ETIMEDOUT || r == -ENOSPC ||
          r == -ENOLINK || r == -EREMOTEIO  || r == -EAGAIN || r == -EIO ||
          r == -ENODATA || r == -EILSEQ || r == -ENOMEM ||
#if defined(__linux__)
          r == -EREMCHG || r == -EBADE
#elif defined(__FreeBSD__)
          r == - BSM_ERRNO_EREMCHG || r == -BSM_ERRNO_EBADE
#endif
          );
}

void KernelDevice::_aio_thread()
{
  dout(10) << __func__ << " start" << dendl;
  int inject_crash_count = 0;
  while (!aio_stop) {
    dout(40) << __func__ << " polling" << dendl;
    int max = cct->_conf->bdev_aio_reap_max;
    aio_t *aio[max];
    int r = io_queue->get_next_completed(cct->_conf->bdev_aio_poll_ms,
                                         aio, max);
    if (r < 0) {
      derr << __func__ << " got " << cpp_strerror(r) << dendl;
      ceph_abort_msg("got unexpected error from io_getevents");
    }
    if (r > 0) {
      dout(30) << __func__ << " got " << r << " completed aios" << dendl;
      for (int i = 0; i < r; ++i) {
        IOContext *ioc = static_cast<IOContext*>(aio[i]->priv);
        _aio_log_finish(ioc, aio[i]->offset, aio[i]->length);
        if (aio[i]->queue_item.is_linked()) {
          std::lock_guard l(debug_queue_lock);
          debug_aio_unlink(*aio[i]);
        }

        // set flag indicating new ios have completed.  we do this *before*
        // any completion or notifications so that any user flush() that
        // follows the observed io completion will include this io.  Note
        // that an earlier, racing flush() could observe and clear this
        // flag, but that also ensures that the IO will be stable before the
        // later flush() occurs.
        io_since_flush.store(true);

        long r = aio[i]->get_return_value();
        if (r < 0) {
          derr << __func__ << " got r=" << r << " (" << cpp_strerror(r) << ")"
               << dendl;
          if (ioc->allow_eio && is_expected_ioerr(r)) {
            derr << __func__ << " translating the error to EIO for upper layer"
                 << dendl;
            ioc->set_return_value(-EIO);
          } else {
            if (is_expected_ioerr(r)) {
              note_io_error_event(
                devname.c_str(),
                path.c_str(),
                r,
#if defined(HAVE_POSIXAIO)
                aio[i]->aio.aiocb.aio_lio_opcode,
#else
                aio[i]->iocb.aio_lio_opcode,
#endif
                aio[i]->offset,
                aio[i]->length);
              ceph_abort_msg(
                "Unexpected IO error. "
                "This may suggest a hardware issue. "
                "Please check your kernel log!");
            }
            ceph_abort_msg(
              "Unexpected IO error. "
              "This may suggest HW issue. Please check your dmesg!");
          }
        } else if (aio[i]->length != (uint64_t)r) {
          derr << "aio to 0x" << std::hex << aio[i]->offset
               << "~" << aio[i]->length << std::dec
               << " but returned: " << r << dendl;
          ceph_abort_msg("unexpected aio return value: does not match length");
        }

        dout(10) << __func__ << " finished aio " << aio[i] << " r " << r
                 << " ioc " << ioc
                 << " with " << (ioc->num_running.load() - 1)
                 << " aios left" << dendl;

        // NOTE: once num_running and we either call the callback or
        // call aio_wake we cannot touch ioc or aio[] as the caller
        // may free it.
        if (ioc->priv) {
          if (--ioc->num_running == 0) {
            aio_callback(aio_callback_priv, ioc->priv);
          }
        } else {
          ioc->try_aio_wake();
        }
      }
    }
    if (cct->_conf->bdev_debug_aio) {
      utime_t now = ceph_clock_now();
      std::lock_guard l(debug_queue_lock);
      if (debug_oldest) {
        if (debug_stall_since == utime_t()) {
          debug_stall_since = now;
        } else {
          if (cct->_conf->bdev_debug_aio_suicide_timeout) {
            utime_t cutoff = now;
            cutoff -= cct->_conf->bdev_debug_aio_suicide_timeout;
            if (debug_stall_since < cutoff) {
              derr << __func__ << " stalled aio " << debug_oldest
                   << " since " << debug_stall_since << ", timeout is "
                   << cct->_conf->bdev_debug_aio_suicide_timeout
                   << "s, suicide" << dendl;
              ceph_abort_msg("stalled aio... buggy kernel or bad device?");
            }
          }
        }
      }
    }
    if (cct->_conf->bdev_inject_crash) {
      ++inject_crash_count;
      if (inject_crash_count * cct->_conf->bdev_aio_poll_ms / 1000 >
          cct->_conf->bdev_inject_crash + cct->_conf->bdev_inject_crash_flush_delay) {
        derr << __func__ << " bdev_inject_crash trigger from aio thread"
             << dendl;
        cct->_log->flush();
        _exit(1);
      }
    }
  }
  dout(10) << __func__ << " end" << dendl;
}

void KernelDevice::_discard_thread()
{
  std::unique_lock l(discard_lock);
  ceph_assert(!discard_started);
  discard_started = true;
  discard_cond.notify_all();
  while (true) {
    ceph_assert(discard_finishing.empty());
    if (discard_queued.empty()) {
      if (discard_stop)
        break;
      dout(20) << __func__ << " sleep" << dendl;
      discard_cond.notify_all(); // for the thread trying to drain...
      discard_cond.wait(l);
      dout(20) << __func__ << " wake" << dendl;
    } else {
      discard_finishing.swap(discard_queued);
      discard_running = true;
      l.unlock();
      dout(20) << __func__ << " finishing" << dendl;
      for (auto p = discard_finishing.begin();p != discard_finishing.end(); ++p) {
        _discard(p.get_start(), p.get_len());
      }

      discard_callback(discard_callback_priv, static_cast<void*>(&discard_finishing));
      discard_finishing.clear();
      l.lock();
      discard_running = false;
    }
  }
  dout(10) << __func__ << " finish" << dendl;
  discard_started = false;
}

int KernelDevice::_queue_discard(interval_set<uint64_t> &to_release)
{
  // if bdev_async_discard enabled on the fly, discard_thread is not started here, fallback to sync discard
  if (!discard_thread.is_started())
    return -1;

  if (to_release.empty())
    return 0;

  std::lock_guard l(discard_lock);
  discard_queued.insert(to_release);
  discard_cond.notify_all();
  return 0;
}

// return true only if _queue_discard succeeded, so caller won't have to do alloc->release
// otherwise false
bool KernelDevice::try_discard(interval_set<uint64_t> &to_release, bool async)
{
  if (!support_discard || !cct->_conf->bdev_enable_discard)
    return false;

  if (async && discard_thread.is_started()) {
    return 0 == _queue_discard(to_release);
  } else {
    for (auto p = to_release.begin(); p != to_release.end(); ++p) {
      _discard(p.get_start(), p.get_len());
    }
  }
  return false;
}

void KernelDevice::_aio_log_start(
  IOContext *ioc,
  uint64_t offset,
  uint64_t length)
{
  dout(20) << __func__ << " 0x" << std::hex << offset << "~" << length
           << std::dec << dendl;
  if (cct->_conf->bdev_debug_inflight_ios) {
    std::lock_guard l(debug_lock);
    if (debug_inflight.intersects(offset, length)) {
      derr << __func__ << " inflight overlap of 0x"
           << std::hex
           << offset << "~" << length << std::dec
           << " with " << debug_inflight << dendl;
      ceph_abort();
    }
    debug_inflight.insert(offset, length);
  }
}

void KernelDevice::debug_aio_link(aio_t& aio)
{
  if (debug_queue.empty()) {
    debug_oldest = &aio;
  }
  debug_queue.push_back(aio);
}

void KernelDevice::debug_aio_unlink(aio_t& aio)
{
  if (aio.queue_item.is_linked()) {
    debug_queue.erase(debug_queue.iterator_to(aio));
    if (debug_oldest == &aio) {
      auto age = cct->_conf->bdev_debug_aio_log_age;
      if (age && debug_stall_since != utime_t()) {
        utime_t cutoff = ceph_clock_now();
        cutoff -= age;
        if (debug_stall_since < cutoff) {
          derr << __func__ << " stalled aio " << debug_oldest
                << " since " << debug_stall_since << ", timeout is "
                << age
                << "s" << dendl;
        }
      }

      if (debug_queue.empty()) {
        debug_oldest = nullptr;
      } else {
        debug_oldest = &debug_queue.front();
      }
      debug_stall_since = utime_t();
    }
  }
}

void KernelDevice::_aio_log_finish(
  IOContext *ioc,
  uint64_t offset,
  uint64_t length)
{
  dout(20) << __func__ << " " << aio << " 0x"
           << std::hex << offset << "~" << length << std::dec << dendl;
  if (cct->_conf->bdev_debug_inflight_ios) {
    std::lock_guard l(debug_lock);
    debug_inflight.erase(offset, length);
  }
}

void KernelDevice::aio_submit(IOContext *ioc)
{
  dout(20) << __func__ << " ioc " << ioc
           << " pending " << ioc->num_pending.load()
           << " running " << ioc->num_running.load()
           << dendl;

  if (ioc->num_pending.load() == 0) {
    return;
  }

  // move these aside, and get our end iterator position now, as the
  // aios might complete as soon as they are submitted and queue more
  // wal aio's.
  list<aio_t>::iterator e = ioc->running_aios.begin();
  ioc->running_aios.splice(e, ioc->pending_aios);

  int pending = ioc->num_pending.load();
  ioc->num_running += pending;
  ioc->num_pending -= pending;
  ceph_assert(ioc->num_pending.load() == 0);  // we should be only thread doing this
  ceph_assert(ioc->pending_aios.size() == 0);

  if (cct->_conf->bdev_debug_aio) {
    list<aio_t>::iterator p = ioc->running_aios.begin();
    while (p != e) {
      dout(30) << __func__ << " " << *p << dendl;
      std::lock_guard l(debug_queue_lock);
      debug_aio_link(*p++);
    }
  }

  void *priv = static_cast<void*>(ioc);
  int r, retries = 0;
  // num of pending aios should not overflow when passed to submit_batch()
  assert(pending <= std::numeric_limits<uint16_t>::max());
  r = io_queue->submit_batch(ioc->running_aios.begin(), e,
                             pending, priv, &retries);

  if (retries)
    derr << __func__ << " retries " << retries << dendl;
  if (r < 0) {
    derr << " aio submit got " << cpp_strerror(r) << dendl;
    ceph_assert(r == 0);
  }
}

int KernelDevice::_sync_write(uint64_t off, bufferlist &bl, bool buffered, int write_hint)
{
  uint64_t len = bl.length();
  dout(5) << __func__ << " 0x" << std::hex << off << "~" << len
          << std::dec << " " << buffermode(buffered) << dendl;
  if (cct->_conf->bdev_inject_crash &&
      rand() % cct->_conf->bdev_inject_crash == 0) {
    derr << __func__ << " bdev_inject_crash: dropping io 0x" << std::hex
         << off << "~" << len << std::dec << dendl;
    ++injecting_crash;
    return 0;
  }
  vector<iovec> iov;
  bl.prepare_iov(&iov);

  auto left = len;
  auto o = off;
  size_t idx = 0;
  do {
    auto r = ::pwritev(choose_fd(buffered, write_hint),
      &iov[idx], iov.size() - idx, o);

    if (r < 0) {
      r = -errno;
      derr << __func__ << " pwritev error: " << cpp_strerror(r) << dendl;
      return r;
    }
    o += r;
    left -= r;
    if (left) {
      // skip fully processed IOVs
      while (idx < iov.size() && (size_t)r >= iov[idx].iov_len) {
        r -= iov[idx++].iov_len;
      }
      // update partially processed one if any
      if (r) {
        ceph_assert(idx < iov.size());
        ceph_assert((size_t)r < iov[idx].iov_len);
        iov[idx].iov_base = static_cast<char*>(iov[idx].iov_base) + r;
        iov[idx].iov_len -= r;
        r = 0;
      }
      ceph_assert(r == 0);
    }
  } while (left);

#ifdef HAVE_SYNC_FILE_RANGE
  if (buffered) {
    // initiate IO and wait till it completes
    auto r = ::sync_file_range(fd_buffereds[WRITE_LIFE_NOT_SET], off, len, SYNC_FILE_RANGE_WRITE|SYNC_FILE_RANGE_WAIT_AFTER|SYNC_FILE_RANGE_WAIT_BEFORE);
    if (r < 0) {
      r = -errno;
      derr << __func__ << " sync_file_range error: " << cpp_strerror(r) << dendl;
      return r;
    }
  }
#endif

  io_since_flush.store(true);

  return 0;
}

int KernelDevice::write(
  uint64_t off,
  bufferlist &bl,
  bool buffered,
  int write_hint)
{
  uint64_t len = bl.length();
  dout(20) << __func__ << " 0x" << std::hex << off << "~" << len << std::dec
           << " " << buffermode(buffered) 
           << dendl;
  ceph_assert(is_valid_io(off, len));
  if (cct->_conf->objectstore_blackhole) {
    lderr(cct) << __func__ << " objectstore_blackhole=true, throwing out IO"
               << dendl;
    return 0;
  }

  if ((!buffered || bl.get_num_buffers() >= IOV_MAX) &&
      bl.rebuild_aligned_size_and_memory(block_size, block_size, IOV_MAX)) {
    dout(20) << __func__ << " rebuilding buffer to be aligned" << dendl;
  }
  dout(40) << "data:\n";
  bl.hexdump(*_dout);
  *_dout << dendl;

  return _sync_write(off, bl, buffered, write_hint);
}

int KernelDevice::aio_write(
  uint64_t off,
  bufferlist &bl,
  IOContext *ioc,
  bool buffered,
  int write_hint)
{
  uint64_t len = bl.length();
  dout(20) << __func__ << " 0x" << std::hex << off << "~" << len << std::dec
           << " " << buffermode(buffered)
           << dendl;
  ceph_assert(is_valid_io(off, len));
  if (cct->_conf->objectstore_blackhole) {
    lderr(cct) << __func__ << " objectstore_blackhole=true, throwing out IO"
               << dendl;
    return 0;
  }

  if ((!buffered || bl.get_num_buffers() >= IOV_MAX) &&
      bl.rebuild_aligned_size_and_memory(block_size, block_size, IOV_MAX)) {
    dout(20) << __func__ << " rebuilding buffer to be aligned" << dendl;
  }
  dout(40) << "data:\n";
  bl.hexdump(*_dout);
  *_dout << dendl;

  _aio_log_start(ioc, off, len);

#ifdef HAVE_LIBAIO
  if (aio && dio && !buffered) {
    if (cct->_conf->bdev_inject_crash &&
        rand() % cct->_conf->bdev_inject_crash == 0) {
      derr << __func__ << " bdev_inject_crash: dropping io 0x" << std::hex
           << off << "~" << len << std::dec
           << dendl;
      // generate a real io so that aio_wait behaves properly, but make it
      // a read instead of write, and toss the result.
      ioc->pending_aios.push_back(aio_t(ioc, choose_fd(false, write_hint)));
      ++ioc->num_pending;
      auto& aio = ioc->pending_aios.back();
      aio.bl.push_back(
        ceph::buffer::ptr_node::create(ceph::buffer::create_small_page_aligned(len)));
      aio.bl.prepare_iov(&aio.iov);
      aio.preadv(off, len);
      ++injecting_crash;
    } else {
      if (bl.length() <= RW_IO_MAX) {
        // fast path (non-huge write)
        ioc->pending_aios.push_back(aio_t(ioc, choose_fd(false, write_hint)));
        ++ioc->num_pending;
        auto& aio = ioc->pending_aios.back();
        bl.prepare_iov(&aio.iov);
        aio.bl.claim_append(bl);
        aio.pwritev(off, len);
        dout(30) << aio << dendl;
        dout(5) << __func__ << " 0x" << std::hex << off << "~" << len
                << std::dec << " aio " << &aio << dendl;
      } else {
        // write in RW_IO_MAX-sized chunks
        uint64_t prev_len = 0;
        while (prev_len < bl.length()) {
          bufferlist tmp;
          if (prev_len + RW_IO_MAX < bl.length()) {
            tmp.substr_of(bl, prev_len, RW_IO_MAX);
          } else {
            tmp.substr_of(bl, prev_len, bl.length() - prev_len);
          }
          auto len = tmp.length();
          ioc->pending_aios.push_back(aio_t(ioc, choose_fd(false, write_hint)));
          ++ioc->num_pending;
          auto& aio = ioc->pending_aios.back();
          tmp.prepare_iov(&aio.iov);
          aio.bl.claim_append(tmp);
          aio.pwritev(off + prev_len, len);
          dout(30) << aio << dendl;
          dout(5) << __func__ << " 0x" << std::hex << off + prev_len
                  << "~" << len
                  << std::dec << " aio " << &aio << " (piece)" << dendl;
          prev_len += len;
        }
      }
    }
  } else
#endif
  {
    int r = _sync_write(off, bl, buffered, write_hint);
    _aio_log_finish(ioc, off, len);
    if (r < 0)
      return r;
  }
  return 0;
}

int KernelDevice::_discard(uint64_t offset, uint64_t len)
{
  int r = 0;
  if (cct->_conf->objectstore_blackhole) {
    lderr(cct) << __func__ << " objectstore_blackhole=true, throwing out IO"
               << dendl;
    return 0;
  }
  dout(10) << __func__
           << " 0x" << std::hex << offset << "~" << len << std::dec
           << dendl;
  r = BlkDev{fd_directs[WRITE_LIFE_NOT_SET]}.discard((int64_t)offset, (int64_t)len);
  return r;
}

struct ExplicitHugePagePool {
  using region_queue_t = boost::lockfree::queue<void*>;
  using instrumented_raw = ceph::buffer_instrumentation::instrumented_raw<
    BlockDevice::hugepaged_raw_marker_t>;

  struct mmaped_buffer_raw : public instrumented_raw {
    region_queue_t& region_q; // for recycling

    mmaped_buffer_raw(void* mmaped_region, ExplicitHugePagePool& parent)
      : instrumented_raw(static_cast<char*>(mmaped_region), parent.buffer_size),
        region_q(parent.region_q) {
      // the `mmaped_region` has been passed to `raw` as the buffer's `data`
    }
    ~mmaped_buffer_raw() override {
      // don't delete nor unmmap; recycle the region instead
      region_q.push(data);
    }
  };

  ExplicitHugePagePool(const size_t buffer_size, size_t buffers_in_pool)
    : buffer_size(buffer_size), region_q(buffers_in_pool) {
    while (buffers_in_pool--) {
      void* const mmaped_region = ::mmap(
        nullptr,
        buffer_size,
        PROT_READ | PROT_WRITE,
#if defined(__FreeBSD__)
        // FreeBSD doesn't have MAP_HUGETLB nor MAP_POPULATE but it has
        // a different, more automated / implicit mechanisms. However,
        // we want to mimic the Linux behavior as closely as possible
        // also in the matter of error handling which is the reason
        // behind MAP_ALIGNED_SUPER.
        // See: https://lists.freebsd.org/pipermail/freebsd-questions/2014-August/260578.html
        MAP_PRIVATE | MAP_ANONYMOUS | MAP_PREFAULT_READ | MAP_ALIGNED_SUPER,
#else
        MAP_PRIVATE | MAP_ANONYMOUS | MAP_POPULATE | MAP_HUGETLB,
#endif // __FreeBSD__
        -1,
        0);
      if (mmaped_region == MAP_FAILED) {
        ceph_abort("can't allocate huge buffer;"
                   " /proc/sys/vm/nr_hugepages misconfigured?");
      } else {
        region_q.push(mmaped_region);
      }
    }
  }
  ~ExplicitHugePagePool() {
    void* mmaped_region;
    while (region_q.pop(mmaped_region)) {
      ::munmap(mmaped_region, buffer_size);
    }
  }

  ceph::unique_leakable_ptr<buffer::raw> try_create() {
    if (void* mmaped_region; region_q.pop(mmaped_region)) {
      return ceph::unique_leakable_ptr<buffer::raw> {
        new mmaped_buffer_raw(mmaped_region, *this)
      };
    } else {
      // oops, empty queue.
      return nullptr;
    }
  }

  size_t get_buffer_size() const {
    return buffer_size;
  }

private:
  const size_t buffer_size;
  region_queue_t region_q;
};

struct HugePagePoolOfPools {
  HugePagePoolOfPools(const std::map<size_t, size_t> conf)
    : pools(conf.size(), [conf] (size_t index, auto emplacer) {
        ceph_assert(index < conf.size());
        // it could be replaced with a state-mutating lambda and
        // `conf::erase()` but performance is not a concern here.
        const auto [buffer_size, buffers_in_pool] =
          *std::next(std::begin(conf), index);
        emplacer.emplace(buffer_size, buffers_in_pool);
      }) {
  }

  ceph::unique_leakable_ptr<buffer::raw> try_create(const size_t size) {
    // thankfully to `conf` being a `std::map` we store the pools
    // sorted by buffer sizes. this would allow to clamp to log(n)
    // but I doubt admins want to have dozens of accelerated buffer
    // size. let's keep this simple for now.
    if (auto iter = std::find_if(std::begin(pools), std::end(pools),
                                 [size] (const auto& pool) {
                                   return size == pool.get_buffer_size();
                                 });
        iter != std::end(pools)) {
      return iter->try_create();
    }
    return nullptr;
  }

  static HugePagePoolOfPools from_desc(const std::string& conf);

private:
  // let's have some space inside (for 2 MB and 4 MB perhaps?)
  // NOTE: we need tiny_vector as the boost::lockfree queue inside
  // pool is not-movable.
  ceph::containers::tiny_vector<ExplicitHugePagePool, 2> pools;
};


HugePagePoolOfPools HugePagePoolOfPools::from_desc(const std::string& desc) {
  std::map<size_t, size_t> conf; // buffer_size -> buffers_in_pool
  std::map<std::string, std::string> exploded_str_conf;
  get_str_map(desc, &exploded_str_conf);
  for (const auto& [buffer_size_s, buffers_in_pool_s] : exploded_str_conf) {
    size_t buffer_size, buffers_in_pool;
    if (sscanf(buffer_size_s.c_str(), "%zu", &buffer_size) != 1) {
      ceph_abort("can't parse a key in the configuration");
    }
    if (sscanf(buffers_in_pool_s.c_str(), "%zu", &buffers_in_pool) != 1) {
      ceph_abort("can't parse a value in the configuration");
    }
    conf[buffer_size] = buffers_in_pool;
  }
  return HugePagePoolOfPools{std::move(conf)};
}

// create a buffer basing on user-configurable. it's intended to make
// our buffers THP-able.
ceph::unique_leakable_ptr<buffer::raw> KernelDevice::create_custom_aligned(
  const size_t len,
  IOContext* const ioc) const
{
  // just to preserve the logic of create_small_page_aligned().
  if (len < CEPH_PAGE_SIZE) {
    return ceph::buffer::create_small_page_aligned(len);
  } else {
    static HugePagePoolOfPools hp_pools = HugePagePoolOfPools::from_desc(
      cct->_conf.get_val<std::string>("bdev_read_preallocated_huge_buffers")
    );
    if (auto lucky_raw = hp_pools.try_create(len); lucky_raw) {
      dout(20) << __func__ << " allocated from huge pool"
               << " lucky_raw.data=" << (void*)lucky_raw->get_data()
               << " bdev_read_preallocated_huge_buffers="
               << cct->_conf.get_val<std::string>("bdev_read_preallocated_huge_buffers")
               << dendl;
      ioc->flags |= IOContext::FLAG_DONT_CACHE;
      return lucky_raw;
    } else {
      // fallthrough due to empty buffer pool. this can happen also
      // when the configurable was explicitly set to 0.
      dout(20) << __func__ << " cannot allocate from huge pool"
               << dendl;
    }
  }
  const size_t custom_alignment = cct->_conf->bdev_read_buffer_alignment;
  dout(20) << __func__ << " with the custom alignment;"
           << " len=" << len
           << " custom_alignment=" << custom_alignment
           << dendl;
  return ceph::buffer::create_aligned(len, custom_alignment);
}

int KernelDevice::read(uint64_t off, uint64_t len, bufferlist *pbl,
                      IOContext *ioc,
                      bool buffered)
{
  dout(5) << __func__ << " 0x" << std::hex << off << "~" << len << std::dec
          << " " << buffermode(buffered)
          << dendl;
  ceph_assert(is_valid_io(off, len));

  _aio_log_start(ioc, off, len);

  auto start1 = mono_clock::now();

  auto p = ceph::buffer::ptr_node::create(create_custom_aligned(len, ioc));
  int r = ::pread(choose_fd(buffered,  WRITE_LIFE_NOT_SET),
                  p->c_str(), len, off);
  auto age = cct->_conf->bdev_debug_aio_log_age;
  if (mono_clock::now() - start1 >= make_timespan(age)) {
    derr << __func__ << " stalled read "
         << " 0x" << std::hex << off << "~" << len << std::dec
         << " " << buffermode(buffered)
         << " since " << start1 << ", timeout is "
         << age
         << "s" << dendl;
  }
  if (r < 0) {
    if (ioc->allow_eio && is_expected_ioerr(-errno)) {
      r = -EIO;
    } else {
      r = -errno;
    }
    derr << __func__ << " 0x" << std::hex << off << "~" << std::left
         << std::dec << " error: " << cpp_strerror(r) << dendl;
    goto out;
  }
  ceph_assert((uint64_t)r == len);
  pbl->push_back(std::move(p));

  dout(40) << "data:\n"; 
  pbl->hexdump(*_dout);
  *_dout << dendl;

 out:
  _aio_log_finish(ioc, off, len);
  return r < 0 ? r : 0;
}

int KernelDevice::aio_read(
  uint64_t off,
  uint64_t len,
  bufferlist *pbl,
  IOContext *ioc)
{
  dout(5) << __func__ << " 0x" << std::hex << off << "~" << len << std::dec
          << dendl;

  int r = 0;
#ifdef HAVE_LIBAIO
  if (aio && dio) {
    ceph_assert(is_valid_io(off, len));
    _aio_log_start(ioc, off, len);
    ioc->pending_aios.push_back(aio_t(ioc, fd_directs[WRITE_LIFE_NOT_SET]));
    ++ioc->num_pending;
    aio_t& aio = ioc->pending_aios.back();
    aio.bl.push_back(
      ceph::buffer::ptr_node::create(create_custom_aligned(len, ioc)));
    aio.bl.prepare_iov(&aio.iov);
    aio.preadv(off, len);
    dout(30) << aio << dendl;
    pbl->append(aio.bl);
    dout(5) << __func__ << " 0x" << std::hex << off << "~" << len
            << std::dec << " aio " << &aio << dendl;
  } else
#endif
  {
    r = read(off, len, pbl, ioc, false);
  }

  return r;
}

int KernelDevice::direct_read_unaligned(uint64_t off, uint64_t len, char *buf)
{
  uint64_t aligned_off = p2align(off, block_size);
  uint64_t aligned_len = p2roundup(off+len, block_size) - aligned_off;
  bufferptr p = ceph::buffer::create_small_page_aligned(aligned_len);
  int r = 0;

  auto start1 = mono_clock::now();
  r = ::pread(fd_directs[WRITE_LIFE_NOT_SET], p.c_str(), aligned_len, aligned_off);
  auto age = cct->_conf->bdev_debug_aio_log_age;
  if (mono_clock::now() - start1 >= make_timespan(age)) {
    derr << __func__ << " stalled read "
         << " 0x" << std::hex << off << "~" << len << std::dec
         << " since " << start1 << ", timeout is "
         << age
         << "s" << dendl;
  }

  if (r < 0) {
    r = -errno;
    derr << __func__ << " 0x" << std::hex << off << "~" << len << std::dec
      << " error: " << cpp_strerror(r) << dendl;
    goto out;
  }
  ceph_assert((uint64_t)r == aligned_len);
  memcpy(buf, p.c_str() + (off - aligned_off), len);

  dout(40) << __func__ << " data:\n";
  bufferlist bl;
  bl.append(buf, len);
  bl.hexdump(*_dout);
  *_dout << dendl;

 out:
  return r < 0 ? r : 0;
}

int KernelDevice::read_random(uint64_t off, uint64_t len, char *buf,
                       bool buffered)
{
  dout(5) << __func__ << " 0x" << std::hex << off << "~" << len << std::dec
          << "buffered " << buffered
          << dendl;
  ceph_assert(len > 0);
  ceph_assert(off < size);
  ceph_assert(off + len <= size);
  int r = 0;
  auto age = cct->_conf->bdev_debug_aio_log_age;

  //if it's direct io and unaligned, we have to use a internal buffer
  if (!buffered && ((off % block_size != 0)
                    || (len % block_size != 0)
                    || (uintptr_t(buf) % CEPH_PAGE_SIZE != 0)))
    return direct_read_unaligned(off, len, buf);

  auto start1 = mono_clock::now();
  if (buffered) {
    //buffered read
    auto off0 = off;
    char *t = buf;
    uint64_t left = len;
    while (left > 0) {
      r = ::pread(fd_buffereds[WRITE_LIFE_NOT_SET], t, left, off);
      if (r < 0) {
        r = -errno;
        derr << __func__ << " 0x" << std::hex << off << "~" << left
          << std::dec << " error: " << cpp_strerror(r) << dendl;
        goto out;
      }
      off += r;
      t += r;
      left -= r;
    }
    if (mono_clock::now() - start1 >= make_timespan(age)) {
      derr << __func__ << " stalled read "
           << " 0x" << std::hex << off0 << "~" << len << std::dec
           << " (buffered) since " << start1 << ", timeout is "
           << age
           << "s" << dendl;
    }
  } else {
    //direct and aligned read
    r = ::pread(fd_directs[WRITE_LIFE_NOT_SET], buf, len, off);
    if (mono_clock::now() - start1 >= make_timespan(age)) {
      derr << __func__ << " stalled read "
           << " 0x" << std::hex << off << "~" << len << std::dec
           << " (direct) since " << start1 << ", timeout is "
           << age
           << "s" << dendl;
    }
    if (r < 0) {
      r = -errno;
      derr << __func__ << " direct_aligned_read" << " 0x" << std::hex
           << off << "~" << std::left << std::dec << " error: " << cpp_strerror(r)
        << dendl;
      goto out;
    }
    ceph_assert((uint64_t)r == len);
  }

  dout(40) << __func__ << " data:\n";
  bufferlist bl;
  bl.append(buf, len);
  bl.hexdump(*_dout);
  *_dout << dendl;

 out:
  return r < 0 ? r : 0;
}

int KernelDevice::invalidate_cache(uint64_t off, uint64_t len)
{
  dout(5) << __func__ << " 0x" << std::hex << off << "~" << len << std::dec
          << dendl;
  ceph_assert(off % block_size == 0);
  ceph_assert(len % block_size == 0);
  int r = posix_fadvise(fd_buffereds[WRITE_LIFE_NOT_SET], off, len, POSIX_FADV_DONTNEED);
  if (r) {
    r = -r;
    derr << __func__ << " 0x" << std::hex << off << "~" << len << std::dec
         << " error: " << cpp_strerror(r) << dendl;
  }
  return r;
}