[PATCH v4 12/34] block: Unify bdrv_child_cb_attach()

[Max Reitz]

Make bdrv_child_cb_attach() call bdrv_backing_attach() for children with
a COW role (and drop the reverse call from bdrv_backing_attach()), so it
can be used for any child (with a proper role set).

Because so far no child has a proper role set, we need a temporary new
callback for child_backing.attach that ensures bdrv_backing_attach() is
called for all COW children that do not have their role set yet.

(Also, move bdrv_child_cb_attach() down to group it with
bdrv_inherited_options().)

Signed-off-by: Max Reitz <mre...@redhat.com>
---
 block.c | 27 ++++++++++++++++++++-------
 1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/block.c b/block.c
index b3b978a092..755704a54c 100644
--- a/block.c
+++ b/block.c
@@ -84,6 +84,7 @@ static BlockDriverState *bdrv_open_inherit(const char 
*filename,
 static void bdrv_inherited_options(BdrvChildRole role, bool parent_is_format,
                                    int *child_flags, QDict *child_options,
                                    int parent_flags, QDict *parent_options);
+static void bdrv_child_cb_attach(BdrvChild *child);
 
 /* If non-zero, use only whitelisted block drivers */
 static int use_bdrv_whitelist;
@@ -1099,12 +1100,6 @@ static void bdrv_child_cb_drained_end(BdrvChild *child,
     bdrv_drained_end_no_poll(bs, drained_end_counter);
 }
 
-static void bdrv_child_cb_attach(BdrvChild *child)
-{
-    BlockDriverState *bs = child->opaque;
-    bdrv_apply_subtree_drain(child, bs);
-}
-
 static void bdrv_child_cb_detach(BdrvChild *child)
 {
     BlockDriverState *bs = child->opaque;
@@ -1252,7 +1247,14 @@ static void bdrv_backing_attach(BdrvChild *c)
                     parent->backing_blocker);
     bdrv_op_unblock(backing_hd, BLOCK_OP_TYPE_BACKUP_TARGET,
                     parent->backing_blocker);
+}
 
+/* XXX: Will be removed along with child_backing */
+static void bdrv_child_cb_attach_backing(BdrvChild *c)
+{
+    if (!(c->role & BDRV_CHILD_COW)) {
+        bdrv_backing_attach(c);
+    }
     bdrv_child_cb_attach(c);
 }
 
@@ -1311,7 +1313,7 @@ static int bdrv_backing_update_filename(BdrvChild *c, 
BlockDriverState *base,
 const BdrvChildClass child_backing = {
     .parent_is_bds   = true,
     .get_parent_desc = bdrv_child_get_parent_desc,
-    .attach          = bdrv_backing_attach,
+    .attach          = bdrv_child_cb_attach_backing,
     .detach          = bdrv_backing_detach,
     .inherit_options = bdrv_backing_options,
     .drained_begin   = bdrv_child_cb_drained_begin,
@@ -1403,6 +1405,17 @@ static void bdrv_inherited_options(BdrvChildRole role, 
bool parent_is_format,
     *child_flags = flags;
 }
 
+static void bdrv_child_cb_attach(BdrvChild *child)
+{
+    BlockDriverState *bs = child->opaque;
+
+    if (child->role & BDRV_CHILD_COW) {
+        bdrv_backing_attach(child);
+    }
+
+    bdrv_apply_subtree_drain(child, bs);
+}
+
 static int bdrv_open_flags(BlockDriverState *bs, int flags)
 {
     int open_flags = flags;
-- 
2.26.2