blockdev: acquire AioContext in blockdev-snapshot-delete-internal-sync

Add dataplane support to the blockdev-snapshot-delete-internal-sync QMP
command.  By acquiring the AioContext we avoid race conditions with the
dataplane thread which may also be accessing the BlockDriverState.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

blockdev.c

@@ -1105,6 +1105,7 @@ SnapshotInfo *qmp_blockdev_snapshot_delete_internal_sync(const char *device,
                                                          Error **errp)
 {
     BlockDriverState *bs = bdrv_find(device);
+    AioContext *aio_context;
     QEMUSnapshotInfo sn;
     Error *local_err = NULL;
     SnapshotInfo *info = NULL;
@@ -1128,25 +1129,30 @@ SnapshotInfo *qmp_blockdev_snapshot_delete_internal_sync(const char *device,
         return NULL;
     }
 
+    aio_context = bdrv_get_aio_context(bs);
+    aio_context_acquire(aio_context);
+
     ret = bdrv_snapshot_find_by_id_and_name(bs, id, name, &sn, &local_err);
     if (local_err) {
         error_propagate(errp, local_err);
-        return NULL;
+        goto out_aio_context;
     }
     if (!ret) {
         error_setg(errp,
                    "Snapshot with id '%s' and name '%s' does not exist on "
                    "device '%s'",
                    STR_OR_NULL(id), STR_OR_NULL(name), device);
-        return NULL;
+        goto out_aio_context;
     }
 
     bdrv_snapshot_delete(bs, id, name, &local_err);
     if (local_err) {
         error_propagate(errp, local_err);
-        return NULL;
+        goto out_aio_context;
     }
 
+    aio_context_release(aio_context);
+
     info = g_new0(SnapshotInfo, 1);
     info->id = g_strdup(sn.id_str);
     info->name = g_strdup(sn.name);
@@ -1157,6 +1163,10 @@ SnapshotInfo *qmp_blockdev_snapshot_delete_internal_sync(const char *device,
     info->vm_clock_sec = sn.vm_clock_nsec / 1000000000;
 
     return info;
+
+out_aio_context:
+    aio_context_release(aio_context);
+    return NULL;
 }
 
 /* New and old BlockDriverState structs for group snapshots */

hw/block/dataplane/virtio-blk.c

@@ -198,6 +198,8 @@ void virtio_blk_data_plane_create(VirtIODevice *vdev, VirtIOBlkConf *conf,
     blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_DRIVE_DEL, s->blocker);
     blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_BACKUP_SOURCE, s->blocker);
     blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_COMMIT, s->blocker);
+    blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_INTERNAL_SNAPSHOT_DELETE,
+                   s->blocker);
     blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_MIRROR, s->blocker);
     blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_STREAM, s->blocker);
     blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_REPLACE, s->blocker);