text: /*
   * Data plane event loop
   *
   * Copyright (c) 2003-2008 Fabrice Bellard
   * Copyright (c) 2009-2017 QEMU contributors
   *
   * Permission is hereby granted, free of charge, to any person obtaining a copy
   * of this software and associated documentation files (the "Software"), to deal
   * in the Software without restriction, including without limitation the rights
   * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
   * copies of the Software, and to permit persons to whom the Software is
   * furnished to do so, subject to the following conditions:
   *
   * The above copyright notice and this permission notice shall be included in
   * all copies or substantial portions of the Software.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
   * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
   * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
   * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
   * THE SOFTWARE.
   */
  
  #include "qemu/osdep.h"
  #include "qapi/error.h"
  #include "qemu-common.h"
  #include "block/aio.h"
  #include "block/thread-pool.h"
  #include "qemu/main-loop.h"
  #include "qemu/atomic.h"
  #include "block/raw-aio.h"
  #include "qemu/coroutine_int.h"
  #include "trace.h"
  
  /***********************************************************/
  /* bottom halves (can be seen as timers which expire ASAP) */
  
  struct QEMUBH {
      AioContext *ctx;
      QEMUBHFunc *cb;
      void *opaque;
      QEMUBH *next;
      bool scheduled;
      bool idle;
      bool deleted;
  };
  
  void aio_bh_schedule_oneshot(AioContext *ctx, QEMUBHFunc *cb, void *opaque)
  {
      QEMUBH *bh;
      bh = g_new(QEMUBH, 1);
      *bh = (QEMUBH){
          .ctx = ctx,
          .cb = cb,
          .opaque = opaque,
      };
      qemu_lockcnt_lock(&ctx->list_lock);
      bh->next = ctx->first_bh;
      bh->scheduled = 1;
      bh->deleted = 1;
      /* Make sure that the members are ready before putting bh into list */
      smp_wmb();
      ctx->first_bh = bh;
      qemu_lockcnt_unlock(&ctx->list_lock);
      aio_notify(ctx);
  }
  
  QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque)
  {
      QEMUBH *bh;
      bh = g_new(QEMUBH, 1);
      *bh = (QEMUBH){
          .ctx = ctx,
          .cb = cb,
          .opaque = opaque,
      };
      qemu_lockcnt_lock(&ctx->list_lock);
      bh->next = ctx->first_bh;
      /* Make sure that the members are ready before putting bh into list */
      smp_wmb();
      ctx->first_bh = bh;
      qemu_lockcnt_unlock(&ctx->list_lock);
      return bh;
  }
  
  void aio_bh_call(QEMUBH *bh)
  {
      bh->cb(bh->opaque);
  }
  
  /* Multiple occurrences of aio_bh_poll cannot be called concurrently.
   * The count in ctx->list_lock is incremented before the call, and is
   * not affected by the call.
   */
  int aio_bh_poll(AioContext *ctx)
  {
      QEMUBH *bh, **bhp, *next;
      int ret;
      bool deleted = false;
  
      ret = 0;
      for (bh = atomic_rcu_read(&ctx->first_bh); bh; bh = next) {
          next = atomic_rcu_read(&bh->next);
          /* The atomic_xchg is paired with the one in qemu_bh_schedule.  The
           * implicit memory barrier ensures that the callback sees all writes
           * done by the scheduling thread.  It also ensures that the scheduling
           * thread sees the zero before bh->cb has run, and thus will call
           * aio_notify again if necessary.
           */
          if (atomic_xchg(&bh->scheduled, 0)) {
              /* Idle BHs don't count as progress */
              if (!bh->idle) {
                  ret = 1;
              }
              bh->idle = 0;
              aio_bh_call(bh);
          }
          if (bh->deleted) {
              deleted = true;
          }
      }
  
      /* remove deleted bhs */
      if (!deleted) {
          return ret;
      }
  
      if (qemu_lockcnt_dec_if_lock(&ctx->list_lock)) {
          bhp = &ctx->first_bh;
          while (*bhp) {
              bh = *bhp;
              if (bh->deleted && !bh->scheduled) {
                  *bhp = bh->next;
                  g_free(bh);
              } else {
                  bhp = &bh->next;
              }
          }
          qemu_lockcnt_inc_and_unlock(&ctx->list_lock);
      }
      return ret;
  }
  
  void qemu_bh_schedule_idle(QEMUBH *bh)
  {
      bh->idle = 1;
      /* Make sure that idle & any writes needed by the callback are done
       * before the locations are read in the aio_bh_poll.
       */
      atomic_mb_set(&bh->scheduled, 1);
  }
  
  void qemu_bh_schedule(QEMUBH *bh)
  {
      AioContext *ctx;
  
      ctx = bh->ctx;
      bh->idle = 0;
      /* The memory barrier implicit in atomic_xchg makes sure that:
       * 1. idle & any writes needed by the callback are done before the
       *    locations are read in the aio_bh_poll.
       * 2. ctx is loaded before scheduled is set and the callback has a chance
       *    to execute.
       */
      if (atomic_xchg(&bh->scheduled, 1) == 0) {
          aio_notify(ctx);
      }
  }
  
  
  /* This func is async.
   */
  void qemu_bh_cancel(QEMUBH *bh)
  {
      bh->scheduled = 0;
  }
  
  /* This func is async.The bottom half will do the delete action at the finial
   * end.
   */
  void qemu_bh_delete(QEMUBH *bh)
  {
      bh->scheduled = 0;
      bh->deleted = 1;
  }
  
  int64_t
  aio_compute_timeout(AioContext *ctx)
  {
      int64_t deadline;
      int timeout = -1;
      QEMUBH *bh;
  
      for (bh = atomic_rcu_read(&ctx->first_bh); bh;
           bh = atomic_rcu_read(&bh->next)) {
          if (bh->scheduled) {
              if (bh->idle) {
                  /* idle bottom halves will be polled at least
                   * every 10ms */
                  timeout = 10000000;
              } else {
                  /* non-idle bottom halves will be executed
                   * immediately */
                  return 0;
              }
          }
      }
  
      deadline = timerlistgroup_deadline_ns(&ctx->tlg);
      if (deadline == 0) {
          return 0;
      } else {
          return qemu_soonest_timeout(timeout, deadline);
      }
  }
  
  static gboolean
  aio_ctx_prepare(GSource *source, gint    *timeout)
  {
      AioContext *ctx = (AioContext *) source;
  
      atomic_or(&ctx->notify_me, 1);
  
      /* We assume there is no timeout already supplied */
      *timeout = qemu_timeout_ns_to_ms(aio_compute_timeout(ctx));
  
      if (aio_prepare(ctx)) {
          *timeout = 0;
      }
  
      return *timeout == 0;
  }
  
  static gboolean
  aio_ctx_check(GSource *source)
  {
      AioContext *ctx = (AioContext *) source;
      QEMUBH *bh;
  
      atomic_and(&ctx->notify_me, ~1);
      aio_notify_accept(ctx);
  
      for (bh = ctx->first_bh; bh; bh = bh->next) {
          if (bh->scheduled) {
              return true;
          }
      }
      return aio_pending(ctx) || (timerlistgroup_deadline_ns(&ctx->tlg) == 0);
  }
  
  static gboolean
  aio_ctx_dispatch(GSource     *source,
                   GSourceFunc  callback,
                   gpointer     user_data)
  {
      AioContext *ctx = (AioContext *) source;
  
      assert(callback == NULL);
      aio_dispatch(ctx);
      return true;
  }
  
  static void
  aio_ctx_finalize(GSource     *source)
  {
      AioContext *ctx = (AioContext *) source;
  
      thread_pool_free(ctx->thread_pool);
  
  #ifdef CONFIG_LINUX_AIO
      if (ctx->linux_aio) {
          laio_detach_aio_context(ctx->linux_aio, ctx);
          laio_cleanup(ctx->linux_aio);
          ctx->linux_aio = NULL;
      }
  #endif
  
      assert(QSLIST_EMPTY(&ctx->scheduled_coroutines));
      qemu_bh_delete(ctx->co_schedule_bh);
  
      qemu_lockcnt_lock(&ctx->list_lock);
      assert(!qemu_lockcnt_count(&ctx->list_lock));
      while (ctx->first_bh) {
          QEMUBH *next = ctx->first_bh->next;
  
          /* qemu_bh_delete() must have been called on BHs in this AioContext */
          assert(ctx->first_bh->deleted);
  
          g_free(ctx->first_bh);
          ctx->first_bh = next;
      }
      qemu_lockcnt_unlock(&ctx->list_lock);
  
      aio_set_event_notifier(ctx, &ctx->notifier, false, NULL, NULL);
      event_notifier_cleanup(&ctx->notifier);
      qemu_rec_mutex_destroy(&ctx->lock);
      qemu_lockcnt_destroy(&ctx->list_lock);
      timerlistgroup_deinit(&ctx->tlg);
  }
  
  static GSourceFuncs aio_source_funcs = {
      aio_ctx_prepare,
      aio_ctx_check,
      aio_ctx_dispatch,
      aio_ctx_finalize
  };
  
  GSource *aio_get_g_source(AioContext *ctx)
  {
      g_source_ref(&ctx->source);
      return &ctx->source;
  }
  
  ThreadPool *aio_get_thread_pool(AioContext *ctx)
  {
      if (!ctx->thread_pool) {
          ctx->thread_pool = thread_pool_new(ctx);
      }
      return ctx->thread_pool;
  }
  
  #ifdef CONFIG_LINUX_AIO
  LinuxAioState *aio_get_linux_aio(AioContext *ctx)
  {
      if (!ctx->linux_aio) {
          ctx->linux_aio = laio_init();
          laio_attach_aio_context(ctx->linux_aio, ctx);
      }
      return ctx->linux_aio;
  }
  #endif
  
  void aio_notify(AioContext *ctx)
  {
      /* Write e.g. bh->scheduled before reading ctx->notify_me.  Pairs
       * with atomic_or in aio_ctx_prepare or atomic_add in aio_poll.
       */
      smp_mb();
      if (ctx->notify_me) {
          event_notifier_set(&ctx->notifier);
          atomic_mb_set(&ctx->notified, true);
      }
  }
  
  void aio_notify_accept(AioContext *ctx)
  {
      if (atomic_xchg(&ctx->notified, false)) {
          event_notifier_test_and_clear(&ctx->notifier);
      }
  }
  
  static void aio_timerlist_notify(void *opaque, QEMUClockType type)
  {
      aio_notify(opaque);
  }
  
  static void event_notifier_dummy_cb(EventNotifier *e)
  {
  }
  
  /* Returns true if aio_notify() was called (e.g. a BH was scheduled) */
  static bool event_notifier_poll(void *opaque)
  {
      EventNotifier *e = opaque;
      AioContext *ctx = container_of(e, AioContext, notifier);
  
      return atomic_read(&ctx->notified);
  }
  
  static void co_schedule_bh_cb(void *opaque)
  {
      AioContext *ctx = opaque;
      QSLIST_HEAD(, Coroutine) straight, reversed;
  
      QSLIST_MOVE_ATOMIC(&reversed, &ctx->scheduled_coroutines);
      QSLIST_INIT(&straight);
  
      while (!QSLIST_EMPTY(&reversed)) {
          Coroutine *co = QSLIST_FIRST(&reversed);
          QSLIST_REMOVE_HEAD(&reversed, co_scheduled_next);
          QSLIST_INSERT_HEAD(&straight, co, co_scheduled_next);
      }
  
      while (!QSLIST_EMPTY(&straight)) {
          Coroutine *co = QSLIST_FIRST(&straight);
          QSLIST_REMOVE_HEAD(&straight, co_scheduled_next);
          trace_aio_co_schedule_bh_cb(ctx, co);
          aio_context_acquire(ctx);
          qemu_coroutine_enter(co);
          aio_context_release(ctx);
      }
  }
  
  AioContext *aio_context_new(Error **errp)
  {
      int ret;
      AioContext *ctx;
  
      ctx = (AioContext *) g_source_new(&aio_source_funcs, sizeof(AioContext));
      aio_context_setup(ctx);
  
      ret = event_notifier_init(&ctx->notifier, false);
      if (ret < 0) {
          error_setg_errno(errp, -ret, "Failed to initialize event notifier");
          goto fail;
      }
      g_source_set_can_recurse(&ctx->source, true);
      qemu_lockcnt_init(&ctx->list_lock);
  
      ctx->co_schedule_bh = aio_bh_new(ctx, co_schedule_bh_cb, ctx);
      QSLIST_INIT(&ctx->scheduled_coroutines);
  
      aio_set_event_notifier(ctx, &ctx->notifier,
                             false,
                             (EventNotifierHandler *)
                             event_notifier_dummy_cb,
                             event_notifier_poll);
  #ifdef CONFIG_LINUX_AIO
      ctx->linux_aio = NULL;
  #endif
      ctx->thread_pool = NULL;
      qemu_rec_mutex_init(&ctx->lock);
      timerlistgroup_init(&ctx->tlg, aio_timerlist_notify, ctx);
  
      ctx->poll_ns = 0;
      ctx->poll_max_ns = 0;
      ctx->poll_grow = 0;
      ctx->poll_shrink = 0;
  
      return ctx;
  fail:
      g_source_destroy(&ctx->source);
      return NULL;
  }
  
  void aio_co_schedule(AioContext *ctx, Coroutine *co)
  {
      trace_aio_co_schedule(ctx, co);
      QSLIST_INSERT_HEAD_ATOMIC(&ctx->scheduled_coroutines,
                                co, co_scheduled_next);
      qemu_bh_schedule(ctx->co_schedule_bh);
  }
  
  void aio_co_wake(struct Coroutine *co)
  {
      AioContext *ctx;
  
      /* Read coroutine before co->ctx.  Matches smp_wmb in
       * qemu_coroutine_enter.
       */
      smp_read_barrier_depends();
      ctx = atomic_read(&co->ctx);
  
      aio_co_enter(ctx, co);
  }
  
  void aio_co_enter(AioContext *ctx, struct Coroutine *co)
  {
      if (ctx != qemu_get_current_aio_context()) {
          aio_co_schedule(ctx, co);
          return;
      }
  
      if (qemu_in_coroutine()) {
          Coroutine *self = qemu_coroutine_self();
          assert(self != co);
          QSIMPLEQ_INSERT_TAIL(&self->co_queue_wakeup, co, co_queue_next);
      } else {
          aio_context_acquire(ctx);
          qemu_aio_coroutine_enter(ctx, co);
          aio_context_release(ctx);
      }
  }
  
  void aio_context_ref(AioContext *ctx)
  {
      g_source_ref(&ctx->source);
  }
  
  void aio_context_unref(AioContext *ctx)
  {
      g_source_unref(&ctx->source);
  }
  
  void aio_context_acquire(AioContext *ctx)
  {
      qemu_rec_mutex_lock(&ctx->lock);
  }
  
  void aio_context_release(AioContext *ctx)
  {
      qemu_rec_mutex_unlock(&ctx->lock);
  }
  