blockjob: introduce .drain callback for jobs

This is required to decouple block jobs from running in an
AioContext.  With multiqueue block devices, a BlockDriverState
does not really belong to a single AioContext.

The solution is to first wait until all I/O operations are
complete; then loop in the main thread for the block job to
complete entirely.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Message-Id: <1477565348-5458-3-git-send-email-pbonzini@redhat.com>
Signed-off-by: Fam Zheng <famz@redhat.com>

1 files changed, 27 insertions, 8 deletions

diff --git a/block/mirror.c b/block/mirror.c
index a433e6848c..52f879a158 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -469,7 +469,11 @@ static void mirror_free_init(MirrorBlockJob *s)
     }
 }
 
-static void mirror_drain(MirrorBlockJob *s)
+/* This is also used for the .pause callback. There is no matching
+ * mirror_resume() because mirror_run() will begin iterating again
+ * when the job is resumed.
+ */
+static void mirror_wait_for_all_io(MirrorBlockJob *s)
 {
     while (s->in_flight > 0) {
         mirror_wait_for_io(s);
@@ -528,6 +532,7 @@ static void mirror_exit(BlockJob *job, void *opaque)
     g_free(s->replaces);
     bdrv_op_unblock_all(target_bs, s->common.blocker);
     blk_unref(s->target);
+    s->target = NULL;
     block_job_completed(&s->common, data->ret);
     g_free(data);
     bdrv_drained_end(src);
@@ -582,7 +587,7 @@ static int coroutine_fn mirror_dirty_init(MirrorBlockJob *s)
             sector_num += nb_sectors;
         }
 
-        mirror_drain(s);
+        mirror_wait_for_all_io(s);
     }
 
     /* First part, loop on the sectors and initialize the dirty bitmap.  */
@@ -787,7 +792,7 @@ immediate_exit:
          * the target is a copy of the source.
          */
         assert(ret < 0 || (!s->synced && block_job_is_cancelled(&s->common)));
-        mirror_drain(s);
+        mirror_wait_for_all_io(s);
     }
 
     assert(s->in_flight == 0);
@@ -872,14 +877,11 @@ static void mirror_complete(BlockJob *job, Error **errp)
     block_job_enter(&s->common);
 }
 
-/* There is no matching mirror_resume() because mirror_run() will begin
- * iterating again when the job is resumed.
- */
-static void coroutine_fn mirror_pause(BlockJob *job)
+static void mirror_pause(BlockJob *job)
 {
     MirrorBlockJob *s = container_of(job, MirrorBlockJob, common);
 
-    mirror_drain(s);
+    mirror_wait_for_all_io(s);
 }
 
 static void mirror_attached_aio_context(BlockJob *job, AioContext *new_context)
@@ -889,6 +891,21 @@ static void mirror_attached_aio_context(BlockJob *job, AioContext *new_context)
     blk_set_aio_context(s->target, new_context);
 }
 
+static void mirror_drain(BlockJob *job)
+{
+    MirrorBlockJob *s = container_of(job, MirrorBlockJob, common);
+
+    /* Need to keep a reference in case blk_drain triggers execution
+     * of mirror_complete...
+     */
+    if (s->target) {
+        BlockBackend *target = s->target;
+        blk_ref(target);
+        blk_drain(target);
+        blk_unref(target);
+    }
+}
+
 static const BlockJobDriver mirror_job_driver = {
     .instance_size          = sizeof(MirrorBlockJob),
     .job_type               = BLOCK_JOB_TYPE_MIRROR,
@@ -896,6 +913,7 @@ static const BlockJobDriver mirror_job_driver = {
     .complete               = mirror_complete,
     .pause                  = mirror_pause,
     .attached_aio_context   = mirror_attached_aio_context,
+    .drain                  = mirror_drain,
 };
 
 static const BlockJobDriver commit_active_job_driver = {
@@ -905,6 +923,7 @@ static const BlockJobDriver commit_active_job_driver = {
     .complete               = mirror_complete,
     .pause                  = mirror_pause,
     .attached_aio_context   = mirror_attached_aio_context,
+    .drain                  = mirror_drain,
 };
 
 static void mirror_start_job(const char *job_id, BlockDriverState *bs,