blockjob: Pause job on draining any job BDS

Block jobs already paused themselves when their main BlockBackend
entered a drained section. This is not good enough: We also want to
pause a block job and may not submit new requests if, for example, the
mirror target node should be drained.

This implements .drained_begin/end callbacks in child_job in order to
consider all block nodes related to the job, and removes the
BlockBackend callbacks which are unnecessary now because the root of the
job main BlockBackend is always referenced with a child_job, too.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>

blockjob.c

@@ -234,26 +234,23 @@ static char *child_job_get_parent_desc(BdrvChild *c)
                            job->id);
 }
 
-static const BdrvChildRole child_job = {
-    .get_parent_desc    = child_job_get_parent_desc,
-    .stay_at_node       = true,
-};
-
-static void block_job_drained_begin(void *opaque)
+static void child_job_drained_begin(BdrvChild *c)
 {
-    BlockJob *job = opaque;
+    BlockJob *job = c->opaque;
     block_job_pause(job);
 }
 
-static void block_job_drained_end(void *opaque)
+static void child_job_drained_end(BdrvChild *c)
 {
-    BlockJob *job = opaque;
+    BlockJob *job = c->opaque;
     block_job_resume(job);
 }
 
-static const BlockDevOps block_job_dev_ops = {
-    .drained_begin = block_job_drained_begin,
-    .drained_end = block_job_drained_end,
+static const BdrvChildRole child_job = {
+    .get_parent_desc    = child_job_get_parent_desc,
+    .drained_begin      = child_job_drained_begin,
+    .drained_end        = child_job_drained_end,
+    .stay_at_node       = true,
 };
 
 void block_job_remove_all_bdrv(BlockJob *job)
@@ -715,7 +712,6 @@ void *block_job_create(const char *job_id, const BlockJobDriver *driver,
     block_job_add_bdrv(job, "main node", bs, 0, BLK_PERM_ALL, &error_abort);
     bs->job = job;
 
-    blk_set_dev_ops(blk, &block_job_dev_ops, job);
     bdrv_op_unblock(bs, BLOCK_OP_TYPE_DATAPLANE, job->blocker);
 
     QLIST_INSERT_HEAD(&block_jobs, job, job_list);