block: Introduce bdrv_unref_child()

This is the counterpart for bdrv_open_child(). It decreases the
reference count of the child BDS and removes it from the list of
children of the given parent BDS.

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

2 files changed, 22 insertions, 2 deletions

diff --git a/block.c b/block.c
index 029feeb7f9..b723cf2858 100644
--- a/block.c
+++ b/block.c
@@ -1117,6 +1117,24 @@ static BdrvChild *bdrv_attach_child(BlockDriverState *parent_bs,
     return child;
 }
 
+static void bdrv_detach_child(BdrvChild *child)
+{
+    QLIST_REMOVE(child, next);
+    g_free(child);
+}
+
+void bdrv_unref_child(BlockDriverState *parent, BdrvChild *child)
+{
+    BlockDriverState *child_bs = child->bs;
+
+    if (child->bs->inherits_from == parent) {
+        child->bs->inherits_from = NULL;
+    }
+
+    bdrv_detach_child(child);
+    bdrv_unref(child_bs);
+}
+
 void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd)
 {
 
@@ -1884,11 +1902,12 @@ void bdrv_close(BlockDriverState *bs)
         BdrvChild *child, *next;
 
         QLIST_FOREACH_SAFE(child, &bs->children, next, next) {
+            /* TODO Remove bdrv_unref() from drivers' close function and use
+             * bdrv_unref_child() here */
             if (child->bs->inherits_from == bs) {
                 child->bs->inherits_from = NULL;
             }
-            QLIST_REMOVE(child, next);
-            g_free(child);
+            bdrv_detach_child(child);
         }
 
         if (bs->backing_hd) {
diff --git a/include/block/block.h b/include/block/block.h
index 50487726f5..37916f7208 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -513,6 +513,7 @@ void bdrv_disable_copy_on_read(BlockDriverState *bs);
 
 void bdrv_ref(BlockDriverState *bs);
 void bdrv_unref(BlockDriverState *bs);
+void bdrv_unref_child(BlockDriverState *parent, BdrvChild *child);
 
 bool bdrv_op_is_blocked(BlockDriverState *bs, BlockOpType op, Error **errp);
 void bdrv_op_block(BlockDriverState *bs, BlockOpType op, Error *reason);