【ceph学习】ceph如何进行数据的读写（2）

本章摘要

上文说到，librados/IoctxImpl.cc中调用objecter_op和objecter的op_submit函数，进行op请求的封装、加参和提交。
本文详细介绍相关函数的调用。

osdc中的操作

初始化Op对象，提交请求

设置Op对象的时间，oid，操作类型等信息。

//osdc/Objector.h
  // mid-level helpers
  Op *prepare_mutate_op(
    const object_t& oid, const object_locator_t& oloc,
    ObjectOperation& op, const SnapContext& snapc,
    ceph::real_time mtime, int flags,
    Context *oncommit, version_t *objver = NULL,
    osd_reqid_t reqid = osd_reqid_t(),
    ZTracer::Trace *parent_trace = nullptr) {
    Op *o = new Op(oid, oloc, std::move(op.ops), flags | global_op_flags |
           CEPH_OSD_FLAG_WRITE, oncommit, objver,
           nullptr, parent_trace);
    o->priority = op.priority;
    o->mtime = mtime;
    o->snapc = snapc;
    o->out_rval.swap(op.out_rval);
    o->out_bl.swap(op.out_bl);
    o->out_handler.swap(op.out_handler);
    o->out_ec.swap(op.out_ec);
    o->reqid = reqid;
    op.clear();
    return o;
  }

osdc/Objector.cc
// read | write ---------------------------
void Objecter::op_submit(Op *op, ceph_tid_t *ptid, int *ctx_budget)
{
  shunique_lock rl(rwlock, ceph::acquire_shared);
  ceph_tid_t tid = 0;
  if (!ptid)
    ptid = &tid;
  op->trace.event("op submit");
  _op_submit_with_budget(op, rl, ptid, ctx_budget);
}
//
void Objecter::_op_submit_with_budget(Op *op,
                      shunique_lock& sul,
                      ceph_tid_t *ptid,
                      int *ctx_budget)
{

  // throttle.  before we look at any state, because
  // _take_op_budget() may drop our lock while it blocks.
  if (!op->ctx_budgeted || (ctx_budget && (*ctx_budget == -1))) {
    int op_budget = _take_op_budget(op, sul);
    // take and pass out the budget for the first OP
    // in the context session
    if (ctx_budget && (*ctx_budget == -1)) {
      *ctx_budget = op_budget;
    }
  }

  if (osd_timeout > timespan(0)) {
    if (op->tid == 0)
      op->tid = ++last_tid;
    auto tid = op->tid;
    op->ontimeout = timer.add_event(osd_timeout,
                    [this, tid]() {
                      op_cancel(tid, -ETIMEDOUT); });
  }

  _op_submit(op, sul, ptid);
}

计算需要提交到哪个osd上，并建立连接。便于后续发送请求至对应的osd上

void Objecter::_op_submit(Op *op, shunique_lock& sul, ceph_tid_t *ptid)
{
  // rwlock is locked

  ldout(cct, 10) << __func__ << " op " << op << dendl;

  // pick target
  ceph_assert(op->session == NULL);
  OSDSession *s = NULL;

  bool check_for_latest_map = false;
  //计算需要提交到哪个osd上。
  int r = _calc_target(&op->target, nullptr);
  switch(r) {
  case RECALC_OP_TARGET_POOL_DNE:
    check_for_latest_map = true;
    break;
  case RECALC_OP_TARGET_POOL_EIO:
    if (op->has_completion()) {
      op->complete(osdc_errc::pool_eio, -EIO);
    }
    return;
  }

  // Try to get a session, including a retry if we need to take write lock
  //根据osd号，建立session连接
  r = _get_session(op->target.osd, &s, sul);

  _send_op_account(op);

  // send?

  ceph_assert(op->target.flags & (CEPH_OSD_FLAG_READ|CEPH_OSD_FLAG_WRITE));

  bool need_send = false;
  if (op->target.paused) {
    ldout(cct, 10) << " tid " << op->tid << " op " << op << " is paused"
           << dendl;
    _maybe_request_map();
  } else if (!s->is_homeless()) {
    need_send = true;
  } else {
    _maybe_request_map();
  }

  unique_lock sl(s->lock);
  if (op->tid == 0)
    op->tid = ++last_tid;

  _session_op_assign(s, op);
  
  //发送请求
  if (need_send) {
    _send_op(op);
  }

  // Last chance to touch Op here, after giving up session lock it can
  // be freed at any time by response handler.
  ceph_tid_t tid = op->tid;
  if (check_for_latest_map) {
    _send_op_map_check(op);
  }
  if (ptid)
    *ptid = tid;
  op = NULL;

  sl.unlock();
  put_session(s);

  ldout(cct, 5) << num_in_flight << " in flight" << dendl;
}

根据osd的序号，即osd id。建立session信息

/**
 * Look up OSDSession by OSD id.
 *
 * @returns 0 on success, or -EAGAIN if the lock context requires
 * promotion to write.
 */
int Objecter::_get_session(int osd, OSDSession **session,
               shunique_lock& sul)
{
  auto s = new OSDSession(cct, osd);
  osd_sessions[osd] = s;
  s->con = messenger->connect_to_osd(osdmap->get_addrs(osd));
  s->con->set_priv(RefCountedPtr{s});
  logger->inc(l_osdc_osd_session_open);
  logger->set(l_osdc_osd_sessions, osd_sessions.size());
  s->get();
  *session = s;
  ldout(cct, 20) << __func__ << " s=" << s << " osd=" << osd << " "
         << s->get_nref() << dendl;
  return 0;
}

构建osdop的message，发送请求

void Objecter::_send_op(Op *op)
{
  // rwlock is locked
  // op->session->lock is locked

  // backoff?
  auto p = op->session->backoffs.find(op->target.actual_pgid);
  if (p != op->session->backoffs.end()) {
    hobject_t hoid = op->target.get_hobj();
    auto q = p->second.lower_bound(hoid);
    if (q != p->second.begin()) {
      --q;
      if (hoid >= q->second.end) {
        ++q;
      }
    }
    if (q != p->second.end()) {
      ldout(cct, 20) << __func__ << " ? " << q->first << " [" << q->second.begin
             << "," << q->second.end << ")" << dendl;
      int r = cmp(hoid, q->second.begin);
      if (r == 0 || (r > 0 && hoid < q->second.end)) {
        ldout(cct, 10) << __func__ << " backoff " << op->target.actual_pgid
               << " id " << q->second.id << " on " << hoid
               << ", queuing " << op << " tid " << op->tid << dendl;
        return;
      }
    }
  }

  ceph_assert(op->tid > 0);
  //构建MOSDOp对象，Message OSD OP。
  MOSDOp *m = _prepare_osd_op(op);

  if (op->target.actual_pgid != m->get_spg()) {
    ldout(cct, 10) << __func__ << " " << op->tid << " pgid change from "
           << m->get_spg() << " to " << op->target.actual_pgid
           << ", updating and reencoding" << dendl;
    m->set_spg(op->target.actual_pgid);
    m->clear_payload();  // reencode
  }

  ldout(cct, 15) << "_send_op " << op->tid << " to "
         << op->target.actual_pgid << " on osd." << op->session->osd
         << dendl;

  ConnectionRef con = op->session->con;
  ceph_assert(con);

  op->incarnation = op->session->incarnation;

  if (op->trace.valid()) {
    m->trace.init("op msg", nullptr, &op->trace);
  }
  op->session->con->send_message(m);
}

构建MOSDOp，加参数。设置必要参数

Objecter::MOSDOp *Objecter::_prepare_osd_op(Op *op)
{
  // rwlock is locked

  int flags = op->target.flags;
  flags |= CEPH_OSD_FLAG_KNOWN_REDIR;
  flags |= CEPH_OSD_FLAG_SUPPORTSPOOLEIO;

  // Nothing checks this any longer, but needed for compatibility with
  // pre-luminous osds
  flags |= CEPH_OSD_FLAG_ONDISK;

  if (!honor_pool_full)
    flags |= CEPH_OSD_FLAG_FULL_FORCE;

  op->target.paused = false;
  op->stamp = ceph::coarse_mono_clock::now();

  hobject_t hobj = op->target.get_hobj();
  auto m = new MOSDOp(client_inc, op->tid,
              hobj, op->target.actual_pgid,
              osdmap->get_epoch(),
              flags, op->features);

  m->set_snapid(op->snapid);
  m->set_snap_seq(op->snapc.seq);
  m->set_snaps(op->snapc.snaps);

  m->ops = op->ops;
  m->set_mtime(op->mtime);
  m->set_retry_attempt(op->attempts++);

  if (!op->trace.valid() && cct->_conf->osdc_blkin_trace_all) {
    op->trace.init("op", &trace_endpoint);
  }

  if (op->priority)
    m->set_priority(op->priority);
  else
    m->set_priority(cct->_conf->osd_client_op_priority);

  if (op->reqid != osd_reqid_t()) {
    m->set_reqid(op->reqid);
  }

  logger->inc(l_osdc_op_send);
  ssize_t sum = 0;
  for (unsigned i = 0; i < m->ops.size(); i++) {
    sum += m->ops[i].indata.length();
  }
  logger->inc(l_osdc_op_send_bytes, sum);

  return m;
}

发送请求

int AsyncConnection::send_message(Message *m)
{
  FUNCTRACE(async_msgr->cct);
  lgeneric_subdout(async_msgr->cct, ms,
           1) << "-- " << async_msgr->get_myaddrs() << " --> "
              << get_peer_addrs() << " -- "
              << *m << " -- " << m << " con "
              << this
              << dendl;

  if (is_blackhole()) {
    lgeneric_subdout(async_msgr->cct, ms, 0) << __func__ << ceph_entity_type_name(peer_type)
      << " blackhole " << *m << dendl;
    m->put();
    return 0;
  }

  // optimistic think it's ok to encode(actually may broken now)
  if (!m->get_priority())
    m->set_priority(async_msgr->get_default_send_priority());

  m->get_header().src = async_msgr->get_myname();
  m->set_connection(this);

#if defined(WITH_EVENTTRACE)
  if (m->get_type() == CEPH_MSG_OSD_OP)
    OID_EVENT_TRACE_WITH_MSG(m, "SEND_MSG_OSD_OP_BEGIN", true);
  else if (m->get_type() == CEPH_MSG_OSD_OPREPLY)
    OID_EVENT_TRACE_WITH_MSG(m, "SEND_MSG_OSD_OPREPLY_BEGIN", true);
#endif

  if (is_loopback) { //loopback connection
    ldout(async_msgr->cct, 20) << __func__ << " " << *m << " local" << dendl;
    std::lock_guard l(write_lock);
    if (protocol->is_connected()) {
      dispatch_queue->local_delivery(m, m->get_priority());
    } else {
      ldout(async_msgr->cct, 10) << __func__ << " loopback connection closed."
                                 << " Drop message " << m << dendl;
      m->put();
    }
    return 0;
  }

  // we don't want to consider local message here, it's too lightweight which
  // may disturb users
  logger->inc(l_msgr_send_messages);

  protocol->send_message(m);
  return 0;
}

在初始化中，实际选择的是ProtocolV2，该类继承自Protocol。有V1和V2两种。

void ProtocolV2::send_message(Message *m) {
  uint64_t f = connection->get_features();

  // TODO: Currently not all messages supports reencode like MOSDMap, so here
  // only let fast dispatch support messages prepare message
  const bool can_fast_prepare = messenger->ms_can_fast_dispatch(m);
  if (can_fast_prepare) {
    prepare_send_message(f, m);
  }

  std::lock_guard l(connection->write_lock);
  bool is_prepared = can_fast_prepare;
  // "features" changes will change the payload encoding
  if (can_fast_prepare && (!can_write || connection->get_features() != f)) {
    // ensure the correctness of message encoding
    m->clear_payload();
    is_prepared = false;
    ldout(cct, 10) << __func__ << " clear encoded buffer previous " << f
                   << " != " << connection->get_features() << dendl;
  }
  if (state == CLOSED) {
    ldout(cct, 10) << __func__ << " connection closed."
                   << " Drop message " << m << dendl;
    m->put();
  } else {
    ldout(cct, 5) << __func__ << " enqueueing message m=" << m
                  << " type=" << m->get_type() << " " << *m << dendl;
    m->queue_start = ceph::mono_clock::now();
    m->trace.event("async enqueueing message");
    out_queue[m->get_priority()].emplace_back(
      out_queue_entry_t{is_prepared, m});
    ldout(cct, 15) << __func__ << " inline write is denied, reschedule m=" << m
                   << dendl;
    if (((!replacing && can_write) || state == STANDBY) && !write_in_progress) {
      write_in_progress = true;
      connection->center->dispatch_event_external(connection->write_handler);
    }
  }
}

请求发送线程处理

void EventCenter::dispatch_event_external(EventCallbackRef e)
{
  uint64_t num = 0;
  {
    std::lock_guard lock{external_lock};
    if (external_num_events > 0 && *external_events.rbegin() == e) {
      return;
    }
    external_events.push_back(e);
    num = ++external_num_events;
  }
  if (num == 1 && !in_thread())
    wakeup();

  ldout(cct, 30) << __func__ << " " << e << " pending " << num << dendl;
}

std::function NetworkStack::add_thread(Worker* w)
{
  return [this, w]() {
      rename_thread(w->id);
      const unsigned EventMaxWaitUs = 30000000;
      w->center.set_owner();
      ldout(cct, 10) << __func__ << " starting" << dendl;
      w->initialize();
      w->init_done();
      while (!w->done) {
        ldout(cct, 30) << __func__ << " calling event process" << dendl;

        ceph::timespan dur;
        int r = w->center.process_events(EventMaxWaitUs, &dur);
        if (r < 0) {
          ldout(cct, 20) << __func__ << " process events failed: "
                         << cpp_strerror(errno) << dendl;
          // TODO do something?
        }
        w->perf_logger->tinc(l_msgr_running_total_time, dur);
      }
      w->reset();
      w->destroy();
  };
}

int EventCenter::process_events(unsigned timeout_microseconds,  ceph::timespan *working_dur)
{
  struct timeval tv;
  int numevents;
  bool trigger_time = false;
  auto now = clock_type::now();
  clock_type::time_point end_time = now + std::chrono::microseconds(timeout_microseconds);

  auto it = time_events.begin();
  if (it != time_events.end() && end_time >= it->first) {
    trigger_time = true;
    end_time = it->first;

    if (end_time > now) {
      timeout_microseconds = std::chrono::duration_cast(end_time - now).count();
    } else {
      timeout_microseconds = 0;
    }
  }

  bool blocking = pollers.empty() && !external_num_events.load();
  if (!blocking)
    timeout_microseconds = 0;
  tv.tv_sec = timeout_microseconds / 1000000;
  tv.tv_usec = timeout_microseconds % 1000000;

  ldout(cct, 30) << __func__ << " wait second " << tv.tv_sec << " usec " << tv.tv_usec << dendl;
  std::vector fired_events;
  numevents = driver->event_wait(fired_events, &tv);
  auto working_start = ceph::mono_clock::now();
  for (int event_id = 0; event_id < numevents; event_id++) {
    int rfired = 0;
    FileEvent *event;
    EventCallbackRef cb;
    event = _get_file_event(fired_events[event_id].fd);

    /* note the event->mask & mask & ... code: maybe an already processed
    * event removed an element that fired and we still didn't
    * processed, so we check if the event is still valid. */
    if (event->mask & fired_events[event_id].mask & EVENT_READABLE) {
      rfired = 1;
      cb = event->read_cb;
      cb->do_request(fired_events[event_id].fd);
    }

    if (event->mask & fired_events[event_id].mask & EVENT_WRITABLE) {
      if (!rfired || event->read_cb != event->write_cb) {
        cb = event->write_cb;
        cb->do_request(fired_events[event_id].fd);
      }
    }

    ldout(cct, 30) << __func__ << " event_wq process is " << fired_events[event_id].fd
                   << " mask is " << fired_events[event_id].mask << dendl;
  }

  if (trigger_time)
    numevents += process_time_events();

  if (external_num_events.load()) {
    external_lock.lock();
    std::deque cur_process;
    cur_process.swap(external_events);
    external_num_events.store(0);
    external_lock.unlock();
    numevents += cur_process.size();
    while (!cur_process.empty()) {
      EventCallbackRef e = cur_process.front();
      ldout(cct, 30) << __func__ << " do " << e << dendl;
      e->do_request(0);
      cur_process.pop_front();
    }
  }

  if (!numevents && !blocking) {
    for (uint32_t i = 0; i < pollers.size(); i++)
      numevents += pollers[i]->poll();
  }

  if (working_dur)
    *working_dur = ceph::mono_clock::now() - working_start;
  return numevents;
}