block/mirror: Fix child permissions

We cannot use bdrv_child_try_set_perm() to give up all restrictions on
the child edge, and still have bdrv_mirror_top_child_perm() request
BLK_PERM_WRITE.  Fix this by making bdrv_mirror_top_child_perm() return
0/BLK_PERM_ALL when we want to give up all permissions, and replacing
bdrv_child_try_set_perm() by bdrv_child_refresh_perms().

The bdrv_child_try_set_perm() before removing the node with
bdrv_replace_node() is then unnecessary.  No permissions have changed
since the previous invocation of bdrv_child_try_set_perm().
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Reviewed-by: NKevin Wolf <kwolf@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block/mirror.c

@@ -85,6 +85,7 @@ typedef struct MirrorBlockJob {
 
 typedef struct MirrorBDSOpaque {
     MirrorBlockJob *job;
+    bool stop;
 } MirrorBDSOpaque;
 
 struct MirrorOp {
@@ -656,8 +657,9 @@ static int mirror_exit_common(Job *job)
 
     /* We don't access the source any more. Dropping any WRITE/RESIZE is
      * required before it could become a backing file of target_bs. */
-    bdrv_child_try_set_perm(mirror_top_bs->backing, 0, BLK_PERM_ALL,
-                            &error_abort);
+    bs_opaque->stop = true;
+    bdrv_child_refresh_perms(mirror_top_bs, mirror_top_bs->backing,
+                             &error_abort);
     if (!abort && s->backing_mode == MIRROR_SOURCE_BACKING_CHAIN) {
         BlockDriverState *backing = s->is_none_mode ? src : s->base;
         if (backing_bs(target_bs) != backing) {
@@ -704,13 +706,12 @@ static int mirror_exit_common(Job *job)
     g_free(s->replaces);
     bdrv_unref(target_bs);
 
-    /* Remove the mirror filter driver from the graph. Before this, get rid of
+    /*
+     * Remove the mirror filter driver from the graph. Before this, get rid of
      * the blockers on the intermediate nodes so that the resulting state is
-     * valid. Also give up permissions on mirror_top_bs->backing, which might
-     * block the removal. */
+     * valid.
+     */
     block_job_remove_all_bdrv(bjob);
-    bdrv_child_try_set_perm(mirror_top_bs->backing, 0, BLK_PERM_ALL,
-                            &error_abort);
     bdrv_replace_node(mirror_top_bs, backing_bs(mirror_top_bs), &error_abort);
 
     /* We just changed the BDS the job BB refers to (with either or both of the
@@ -1459,6 +1460,18 @@ static void bdrv_mirror_top_child_perm(BlockDriverState *bs, BdrvChild *c,
                                        uint64_t perm, uint64_t shared,
                                        uint64_t *nperm, uint64_t *nshared)
 {
+    MirrorBDSOpaque *s = bs->opaque;
+
+    if (s->stop) {
+        /*
+         * If the job is to be stopped, we do not need to forward
+         * anything to the real image.
+         */
+        *nperm = 0;
+        *nshared = BLK_PERM_ALL;
+        return;
+    }
+
     /* Must be able to forward guest writes to the real image */
     *nperm = 0;
     if (perm & BLK_PERM_WRITE) {
@@ -1681,8 +1694,9 @@ fail:
         job_early_fail(&s->common.job);
     }
 
-    bdrv_child_try_set_perm(mirror_top_bs->backing, 0, BLK_PERM_ALL,
-                            &error_abort);
+    bs_opaque->stop = true;
+    bdrv_child_refresh_perms(mirror_top_bs, mirror_top_bs->backing,
+                             &error_abort);
     bdrv_replace_node(mirror_top_bs, backing_bs(mirror_top_bs), &error_abort);
 
     bdrv_unref(mirror_top_bs);