block: bdrv_append(): don't consume reference

We have too much comments for this feature. It seems better just don't
do it. Most of real users (tests don't count) have to create additional
reference.

Drop also comment in external_snapshot_prepare:
 - bdrv_append doesn't "remove" old bs in common sense, it sounds
   strange
 - the fact that bdrv_append can fail is obvious from the context
 - the fact that we must rollback all changes in transaction abort is
   known (it's the direct role of abort)

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20210428151804.439460-5-vsementsov@virtuozzo.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

2 files changed, 4 insertions, 1 deletions

diff --git a/tests/unit/test-bdrv-drain.c b/tests/unit/test-bdrv-drain.c
index 8a29e33e00..892f7f47d8 100644
--- a/tests/unit/test-bdrv-drain.c
+++ b/tests/unit/test-bdrv-drain.c
@@ -1478,7 +1478,6 @@ static void test_append_to_drained(void)
     g_assert_cmpint(base_s->drain_count, ==, 1);
     g_assert_cmpint(base->in_flight, ==, 0);
 
-    /* Takes ownership of overlay, so we don't have to unref it later */
     bdrv_append(overlay, base, &error_abort);
     g_assert_cmpint(base->in_flight, ==, 0);
     g_assert_cmpint(overlay->in_flight, ==, 0);
@@ -1495,6 +1494,7 @@ static void test_append_to_drained(void)
     g_assert_cmpint(overlay->quiesce_counter, ==, 0);
     g_assert_cmpint(overlay_s->drain_count, ==, 0);
 
+    bdrv_unref(overlay);
     bdrv_unref(base);
     blk_unref(blk);
 }
diff --git a/tests/unit/test-bdrv-graph-mod.c b/tests/unit/test-bdrv-graph-mod.c
index 5b6934e68b..a6064b1863 100644
--- a/tests/unit/test-bdrv-graph-mod.c
+++ b/tests/unit/test-bdrv-graph-mod.c
@@ -138,6 +138,7 @@ static void test_update_perm_tree(void)
     ret = bdrv_append(filter, bs, NULL);
     g_assert_cmpint(ret, <, 0);
 
+    bdrv_unref(filter);
     blk_unref(root);
 }
 
@@ -202,6 +203,7 @@ static void test_should_update_child(void)
     bdrv_append(filter, bs, &error_abort);
     g_assert(target->backing->bs == bs);
 
+    bdrv_unref(filter);
     bdrv_unref(bs);
     blk_unref(root);
 }
@@ -380,6 +382,7 @@ static void test_append_greedy_filter(void)
                       &error_abort);
 
     bdrv_append(fl, base, &error_abort);
+    bdrv_unref(fl);
     bdrv_unref(top);
 }