block/commit: utilize job_exit shim

Change the manual deferment to commit_complete into the implicit
callback to job_exit, renaming commit_complete to commit_exit.

This conversion does change the timing of when job_completed is
called to after the bdrv_replace_node and bdrv_unref calls, which
could have implications for bjob->blk which will now be put down
after this cleanup.

Kevin highlights that we did not take any permissions for that backend
at job creation time, so it is safe to reorder these operations.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-id: 20180830015734.19765-5-jsnow@redhat.com
Reviewed-by: Jeff Cody <jcody@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>

block/commit.c

@@ -68,19 +68,13 @@ static int coroutine_fn commit_populate(BlockBackend *bs, BlockBackend *base,
     return 0;
 }
 
-typedef struct {
-    int ret;
-} CommitCompleteData;
-
-static void commit_complete(Job *job, void *opaque)
+static void commit_exit(Job *job)
 {
     CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
     BlockJob *bjob = &s->common;
-    CommitCompleteData *data = opaque;
     BlockDriverState *top = blk_bs(s->top);
     BlockDriverState *base = blk_bs(s->base);
     BlockDriverState *commit_top_bs = s->commit_top_bs;
-    int ret = data->ret;
     bool remove_commit_top_bs = false;
 
     /* Make sure commit_top_bs and top stay around until bdrv_replace_node() */
@@ -91,10 +85,10 @@ static void commit_complete(Job *job, void *opaque)
      * the normal backing chain can be restored. */
     blk_unref(s->base);
 
-    if (!job_is_cancelled(job) && ret == 0) {
+    if (!job_is_cancelled(job) && job->ret == 0) {
         /* success */
-        ret = bdrv_drop_intermediate(s->commit_top_bs, base,
-                                     s->backing_file_str);
+        job->ret = bdrv_drop_intermediate(s->commit_top_bs, base,
+                                          s->backing_file_str);
     } else {
         /* XXX Can (or should) we somehow keep 'consistent read' blocked even
          * after the failed/cancelled commit job is gone? If we already wrote
@@ -117,9 +111,6 @@ static void commit_complete(Job *job, void *opaque)
      * bdrv_set_backing_hd() to fail. */
     block_job_remove_all_bdrv(bjob);
 
-    job_completed(job, ret);
-    g_free(data);
-
     /* If bdrv_drop_intermediate() didn't already do that, remove the commit
      * filter driver from the backing chain. Do this as the final step so that
      * the 'consistent read' permission can be granted.  */
@@ -137,7 +128,6 @@ static void commit_complete(Job *job, void *opaque)
 static int coroutine_fn commit_run(Job *job, Error **errp)
 {
     CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
-    CommitCompleteData *data;
     int64_t offset;
     uint64_t delay_ns = 0;
     int ret = 0;
@@ -210,9 +200,6 @@ static int coroutine_fn commit_run(Job *job, Error **errp)
 out:
     qemu_vfree(buf);
 
-    data = g_malloc(sizeof(*data));
-    data->ret = ret;
-    job_defer_to_main_loop(&s->common.job, commit_complete, data);
     return ret;
 }
 
@@ -224,6 +211,7 @@ static const BlockJobDriver commit_job_driver = {
         .user_resume   = block_job_user_resume,
         .drain         = block_job_drain,
         .run           = commit_run,
+        .exit          = commit_exit,
     },
 };