[PATCH v6 6/9] block: move supports_backing check to bdrv_set_file_or_backing_noperm()

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

Move supports_backing check of bdrv_reopen_parse_backing to called
(through bdrv_set_backing_noperm()) bdrv_set_file_or_backing_noperm()
function. The check applies to general case, so it's appropriate for
bdrv_set_file_or_backing_noperm().

We have to declare backing support for two test drivers, otherwise new
check fails.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 block.c                          | 29 +++++++++++++++--------------
 tests/unit/test-bdrv-drain.c     |  1 +
 tests/unit/test-bdrv-graph-mod.c |  1 +
 3 files changed, 17 insertions(+), 14 deletions(-)

diff --git a/block.c b/block.c
index 1717e5cb98..f835b576a9 100644
--- a/block.c
+++ b/block.c
@@ -3152,6 +3152,14 @@ static int bdrv_set_file_or_backing_noperm(BlockDriverState *parent_bs,
         return -EPERM;
     }
 
+    if (is_backing && !parent_bs->drv->is_filter &&
+        !parent_bs->drv->supports_backing)
+    {
+        error_setg(errp, "Driver '%s' of node '%s' does not support backing "
+                   "files", parent_bs->drv->format_name, parent_bs->node_name);
+        return -EINVAL;
+    }
+
     if (parent_bs->drv->is_filter) {
         role = BDRV_CHILD_FILTERED | BDRV_CHILD_PRIMARY;
     } else if (is_backing) {
@@ -4278,20 +4286,13 @@ static int bdrv_reopen_parse_backing(BDRVReopenState *reopen_state,
         }
     }
 
-    /*
-     * Ensure that @bs can really handle backing files, because we are
-     * about to give it one (or swap the existing one)
-     */
-    if (bs->drv->is_filter) {
-        /* Filters always have a file or a backing child */
-        if (!bs->backing) {
-            error_setg(errp, "'%s' is a %s filter node that does not support a "
-                       "backing child", bs->node_name, bs->drv->format_name);
-            return -EINVAL;
-        }
-    } else if (!bs->drv->supports_backing) {
-        error_setg(errp, "Driver '%s' of node '%s' does not support backing "
-                   "files", bs->drv->format_name, bs->node_name);
+    if (bs->drv->is_filter && !bs->backing) {
+        /*
+         * Filters always have a file or a backing child, so we are trying to
+         * change wrong child
+         */
+        error_setg(errp, "'%s' is a %s filter node that does not support a "
+                   "backing child", bs->node_name, bs->drv->format_name);
         return -EINVAL;
     }
 
diff --git a/tests/unit/test-bdrv-drain.c b/tests/unit/test-bdrv-drain.c
index 892f7f47d8..ce071b5fc5 100644
--- a/tests/unit/test-bdrv-drain.c
+++ b/tests/unit/test-bdrv-drain.c
@@ -95,6 +95,7 @@ static int bdrv_test_change_backing_file(BlockDriverState *bs,
 static BlockDriver bdrv_test = {
     .format_name            = "test",
     .instance_size          = sizeof(BDRVTestState),
+    .supports_backing       = true,
 
     .bdrv_close             = bdrv_test_close,
     .bdrv_co_preadv         = bdrv_test_co_preadv,
diff --git a/tests/unit/test-bdrv-graph-mod.c b/tests/unit/test-bdrv-graph-mod.c
index 88f25c0cdb..a6e3bb79be 100644
--- a/tests/unit/test-bdrv-graph-mod.c
+++ b/tests/unit/test-bdrv-graph-mod.c
@@ -41,6 +41,7 @@ static void no_perm_default_perms(BlockDriverState *bs, BdrvChild *c,
 
 static BlockDriver bdrv_no_perm = {
     .format_name = "no-perm",
+    .supports_backing = true,
     .bdrv_child_perm = no_perm_default_perms,
 };
 
-- 
2.29.2