[PATCH v3 07/10] migration: Replace QemuSemaphore with QemuEvent

[Akihiko Odaki <akihiko.odaki@daynix.com>]

rp_pong_acks tells if it has ever received one pong. QemuEvent is
better suited for this usage because it represents a boolean rather
than integer and will not decrement with the wait operation.

pause_event can utilize qemu_event_reset() to discard events.

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
---
 migration/migration.h |  6 +++---
 migration/migration.c | 29 +++++++++++++----------------
 2 files changed, 16 insertions(+), 19 deletions(-)

diff --git a/migration/migration.h b/migration/migration.h
index d53f7cad84d8..11dba5f4da77 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -342,11 +342,11 @@ struct MigrationState {
          */
         QemuSemaphore rp_sem;
         /*
-         * We post to this when we got one PONG from dest. So far it's an
+         * We set this when we got one PONG from dest. So far it's an
          * easy way to know the main channel has successfully established
          * on dest QEMU.
          */
-        QemuSemaphore rp_pong_acks;
+        QemuEvent rp_pong_acks;
     } rp_state;
 
     double mbps;
@@ -379,7 +379,7 @@ struct MigrationState {
     QemuSemaphore wait_unplug_sem;
 
     /* Migration is paused due to pause-before-switchover */
-    QemuSemaphore pause_sem;
+    QemuEvent pause_event;
 
     /* The semaphore is used to notify COLO thread that failover is finished */
     QemuSemaphore colo_exit_sem;
diff --git a/migration/migration.c b/migration/migration.c
index 4697732bef91..053c23c58d82 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -1630,7 +1630,7 @@ void migration_cancel(void)
         }
         /* If the migration is paused, kick it out of the pause */
         if (old_state == MIGRATION_STATUS_PRE_SWITCHOVER) {
-            qemu_sem_post(&s->pause_sem);
+            qemu_event_set(&s->pause_event);
         }
         migrate_set_state(&s->state, old_state, MIGRATION_STATUS_CANCELLING);
     } while (s->state != MIGRATION_STATUS_CANCELLING);
@@ -2342,7 +2342,7 @@ void qmp_migrate_continue(MigrationStatus state, Error **errp)
                    MigrationStatus_str(s->state));
         return;
     }
-    qemu_sem_post(&s->pause_sem);
+    qemu_event_set(&s->pause_event);
 }
 
 int migration_rp_wait(MigrationState *s)
@@ -2550,7 +2550,7 @@ static void *source_return_path_thread(void *opaque)
         case MIG_RP_MSG_PONG:
             tmp32 = ldl_be_p(buf);
             trace_source_return_path_thread_pong(tmp32);
-            qemu_sem_post(&ms->rp_state.rp_pong_acks);
+            qemu_event_set(&ms->rp_state.rp_pong_acks);
             break;
 
         case MIG_RP_MSG_REQ_PAGES:
@@ -2693,7 +2693,7 @@ static inline void
 migration_wait_main_channel(MigrationState *ms)
 {
     /* Wait until one PONG message received */
-    qemu_sem_wait(&ms->rp_state.rp_pong_acks);
+    qemu_event_wait(&ms->rp_state.rp_pong_acks);
 }
 
 /*
@@ -2911,21 +2911,18 @@ static bool migration_switchover_prepare(MigrationState *s)
         return true;
     }
 
-    /* Since leaving this state is not atomic with posting the semaphore
+    /*
+     * Since leaving this state is not atomic with setting the event
      * it's possible that someone could have issued multiple migrate_continue
-     * and the semaphore is incorrectly positive at this point;
-     * the docs say it's undefined to reinit a semaphore that's already
-     * init'd, so use timedwait to eat up any existing posts.
+     * and the event is incorrectly set at this point so reset it.
      */
-    while (qemu_sem_timedwait(&s->pause_sem, 1) == 0) {
-        /* This block intentionally left blank */
-    }
+    qemu_event_reset(&s->pause_event);
 
     /* Update [POSTCOPY_]ACTIVE to PRE_SWITCHOVER */
     migrate_set_state(&s->state, s->state, MIGRATION_STATUS_PRE_SWITCHOVER);
     bql_unlock();
 
-    qemu_sem_wait(&s->pause_sem);
+    qemu_event_wait(&s->pause_event);
 
     bql_lock();
     /*
@@ -4057,10 +4054,10 @@ static void migration_instance_finalize(Object *obj)
     qemu_mutex_destroy(&ms->qemu_file_lock);
     qemu_sem_destroy(&ms->wait_unplug_sem);
     qemu_sem_destroy(&ms->rate_limit_sem);
-    qemu_sem_destroy(&ms->pause_sem);
+    qemu_event_destroy(&ms->pause_event);
     qemu_sem_destroy(&ms->postcopy_pause_sem);
     qemu_sem_destroy(&ms->rp_state.rp_sem);
-    qemu_sem_destroy(&ms->rp_state.rp_pong_acks);
+    qemu_event_destroy(&ms->rp_state.rp_pong_acks);
     qemu_sem_destroy(&ms->postcopy_qemufile_src_sem);
     error_free(ms->error);
 }
@@ -4072,14 +4069,14 @@ static void migration_instance_init(Object *obj)
     ms->state = MIGRATION_STATUS_NONE;
     ms->mbps = -1;
     ms->pages_per_second = -1;
-    qemu_sem_init(&ms->pause_sem, 0);
+    qemu_event_init(&ms->pause_event, false);
     qemu_mutex_init(&ms->error_mutex);
 
     migrate_params_init(&ms->parameters);
 
     qemu_sem_init(&ms->postcopy_pause_sem, 0);
     qemu_sem_init(&ms->rp_state.rp_sem, 0);
-    qemu_sem_init(&ms->rp_state.rp_pong_acks, 0);
+    qemu_event_init(&ms->rp_state.rp_pong_acks, false);
     qemu_sem_init(&ms->rate_limit_sem, 0);
     qemu_sem_init(&ms->wait_unplug_sem, 0);
     qemu_sem_init(&ms->postcopy_qemufile_src_sem, 0);

-- 
2.49.0