On Wed, Oct 18, 2017 at 06:40:09PM +0100, Dr. David Alan Gilbert (git) wrote: > From: "Dr. David Alan Gilbert" <dgilb...@redhat.com> > > Wait for a semaphore before completing the migration, > if the previously added capability was enabled. > > Signed-off-by: Dr. David Alan Gilbert <dgilb...@redhat.com> > --- > migration/migration.c | 38 ++++++++++++++++++++++++++++++++++++++ > migration/migration.h | 3 +++ > 2 files changed, 41 insertions(+) > > diff --git a/migration/migration.c b/migration/migration.c > index 86ae0292f0..6c6d5e2c75 100644 > --- a/migration/migration.c > +++ b/migration/migration.c > @@ -1968,6 +1968,39 @@ fail: > } > > /** > + * migration_maybe_pause: Pause if required to by > + * migrate_pause_before_switchover called with the iothread locked > + * Returns: 0 on success > + */ > +static int migration_maybe_pause(MigrationState *s, int > *current_active_state) > +{ > + if (!migrate_pause_before_switchover()) { > + return 0; > + } > + > + /* Since leaving this state is not atomic with posting the semaphore > + * 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. > + */ > + while (qemu_sem_timedwait(&s->pause_sem, 1) == 0) { > + /* This block intentionally left blank */ > + }
Not sure whether worth generalizing this (along with the comment) into a function like qemu_sem_consume_all(), but I'm fine with either way, especially if no respin is planned. (The comment is not really migration specific as well - IMHO it's a general problem for many other semaphores) Reviewed-by: Peter Xu <pet...@redhat.com> > + > + qemu_mutex_unlock_iothread(); > + migrate_set_state(&s->state, *current_active_state, > + MIGRATION_STATUS_PRE_SWITCHOVER); > + qemu_sem_wait(&s->pause_sem); > + migrate_set_state(&s->state, MIGRATION_STATUS_PRE_SWITCHOVER, > + MIGRATION_STATUS_DEVICE); > + *current_active_state = MIGRATION_STATUS_DEVICE; > + qemu_mutex_lock_iothread(); > + > + return s->state == MIGRATION_STATUS_DEVICE ? 0 : -EINVAL; > +} > + > +/** > * migration_completion: Used by migration_thread when there's not much left. > * The caller 'breaks' the loop when this returns. > * > @@ -1993,6 +2026,9 @@ static void migration_completion(MigrationState *s, int > current_active_state, > bool inactivate = !migrate_colo_enabled(); > ret = vm_stop_force_state(RUN_STATE_FINISH_MIGRATE); > if (ret >= 0) { > + ret = migration_maybe_pause(s, ¤t_active_state); > + } > + if (ret >= 0) { > qemu_file_set_rate_limit(s->to_dst_file, INT64_MAX); > ret = qemu_savevm_state_complete_precopy(s->to_dst_file, > false, > inactivate); > @@ -2373,6 +2409,7 @@ static void migration_instance_finalize(Object *obj) > > g_free(params->tls_hostname); > g_free(params->tls_creds); > + qemu_sem_destroy(&ms->pause_sem); > } > > static void migration_instance_init(Object *obj) > @@ -2383,6 +2420,7 @@ static void migration_instance_init(Object *obj) > ms->state = MIGRATION_STATUS_NONE; > ms->xbzrle_cache_size = DEFAULT_MIGRATE_CACHE_SIZE; > ms->mbps = -1; > + qemu_sem_init(&ms->pause_sem, 0); > > params->tls_hostname = g_strdup(""); > params->tls_creds = g_strdup(""); > diff --git a/migration/migration.h b/migration/migration.h > index 969866303e..cd988a99b9 100644 > --- a/migration/migration.h > +++ b/migration/migration.h > @@ -121,6 +121,9 @@ struct MigrationState > /* Flag set once the migration thread called bdrv_inactivate_all */ > bool block_inactive; > > + /* Migration is paused due to pause-before-switchover */ > + QemuSemaphore pause_sem; > + > /* The semaphore is used to notify COLO thread that failover is finished > */ > QemuSemaphore colo_exit_sem; > > -- > 2.13.6 > -- Peter Xu