[PATCH v2 23/36] block: adapt bdrv_append() for inserting filters

[Vladimir Sementsov-Ogievskiy]

bdrv_append is not very good for inserting filters: it does extra
permission update as part of bdrv_set_backing_hd(). During this update
filter may conflict with other parents of top_bs.

Instead, let's first do all graph modifications and after it update
permissions.

Note: bdrv_append() is still only works for backing-child based
filters. It's something to improve later.

It simplifies the fact that bdrv_append() used to append new nodes,
without backing child. Let's add an assertion.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 block.c | 28 +++++++++++++++++-----------
 1 file changed, 17 insertions(+), 11 deletions(-)

diff --git a/block.c b/block.c
index 02da1a90bc..7094922509 100644
--- a/block.c
+++ b/block.c
@@ -4998,22 +4998,28 @@ int bdrv_replace_node(BlockDriverState *from, 
BlockDriverState *to,
 int bdrv_append(BlockDriverState *bs_new, BlockDriverState *bs_top,
                 Error **errp)
 {
-    Error *local_err = NULL;
+    int ret;
+    GSList *tran = NULL;
 
-    bdrv_set_backing_hd(bs_new, bs_top, &local_err);
-    if (local_err) {
-        error_propagate(errp, local_err);
-        return -EPERM;
+    assert(!bs_new->backing);
+
+    ret = bdrv_attach_child_noperm(bs_new, bs_top, "backing",
+                                   &child_of_bds, bdrv_backing_role(bs_new),
+                                   &bs_new->backing, &tran, errp);
+    if (ret < 0) {
+        goto out;
     }
 
-    bdrv_replace_node(bs_top, bs_new, &local_err);
-    if (local_err) {
-        error_propagate(errp, local_err);
-        bdrv_set_backing_hd(bs_new, NULL, &error_abort);
-        return -EPERM;
+    ret = bdrv_replace_node_noperm(bs_top, bs_new, true, &tran, errp);
+    if (ret < 0) {
+        goto out;
     }
 
-    return 0;
+    ret = bdrv_refresh_perms(bs_new, errp);
+out:
+    tran_finalize(tran, ret);
+
+    return ret;
 }
 
 static void bdrv_delete(BlockDriverState *bs)
-- 
2.21.3