block: make bdrv_unset_inherits_from to be a transaction action

To be used in the further commit.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20210428151804.439460-27-vsementsov@virtuozzo.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block.c

@@ -3205,11 +3205,49 @@ void bdrv_root_unref_child(BdrvChild *child)
     bdrv_unref(child_bs);
 }
 
+typedef struct BdrvSetInheritsFrom {
+    BlockDriverState *bs;
+    BlockDriverState *old_inherits_from;
+} BdrvSetInheritsFrom;
+
+static void bdrv_set_inherits_from_abort(void *opaque)
+{
+    BdrvSetInheritsFrom *s = opaque;
+
+    s->bs->inherits_from = s->old_inherits_from;
+}
+
+static TransactionActionDrv bdrv_set_inherits_from_drv = {
+    .abort = bdrv_set_inherits_from_abort,
+    .clean = g_free,
+};
+
+/* @tran is allowed to be NULL. In this case no rollback is possible */
+static void bdrv_set_inherits_from(BlockDriverState *bs,
+                                   BlockDriverState *new_inherits_from,
+                                   Transaction *tran)
+{
+    if (tran) {
+        BdrvSetInheritsFrom *s = g_new(BdrvSetInheritsFrom, 1);
+
+        *s = (BdrvSetInheritsFrom) {
+            .bs = bs,
+            .old_inherits_from = bs->inherits_from,
+        };
+
+        tran_add(tran, &bdrv_set_inherits_from_drv, s);
+    }
+
+    bs->inherits_from = new_inherits_from;
+}
+
 /**
  * Clear all inherits_from pointers from children and grandchildren of
  * @root that point to @root, where necessary.
+ * @tran is allowed to be NULL. In this case no rollback is possible
  */
-static void bdrv_unset_inherits_from(BlockDriverState *root, BdrvChild *child)
+static void bdrv_unset_inherits_from(BlockDriverState *root, BdrvChild *child,
+                                     Transaction *tran)
 {
     BdrvChild *c;
 
@@ -3224,12 +3262,12 @@ static void bdrv_unset_inherits_from(BlockDriverState *root, BdrvChild *child)
             }
         }
         if (c == NULL) {
-            child->bs->inherits_from = NULL;
+            bdrv_set_inherits_from(child->bs, NULL, tran);
         }
     }
 
     QLIST_FOREACH(c, &child->bs->children, next) {
-        bdrv_unset_inherits_from(root, c);
+        bdrv_unset_inherits_from(root, c, tran);
     }
 }
 
@@ -3240,7 +3278,7 @@ void bdrv_unref_child(BlockDriverState *parent, BdrvChild *child)
         return;
     }
 
-    bdrv_unset_inherits_from(parent, child);
+    bdrv_unset_inherits_from(parent, child, NULL);
     bdrv_root_unref_child(child);
 }