block: Add bdrv_default_perms()

This callback can be used by BDSs that use child_of_bds with the
appropriate BdrvChildRole for their children.

Also, make bdrv_format_default_perms() use it for child_of_bds children
(just a temporary solution until we can drop bdrv_format_default_perms()
altogether).

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200513110544.176672-20-mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block.c

@@ -2596,6 +2596,13 @@ void bdrv_format_default_perms(BlockDriverState *bs, BdrvChild *c,
                                uint64_t *nperm, uint64_t *nshared)
 {
     bool backing = (child_class == &child_backing);
+
+    if (child_class == &child_of_bds) {
+        bdrv_default_perms(bs, c, child_class, role, reopen_queue,
+                           perm, shared, nperm, nshared);
+        return;
+    }
+
     assert(child_class == &child_backing || child_class == &child_file);
 
     if (!backing) {
@@ -2607,6 +2614,31 @@ void bdrv_format_default_perms(BlockDriverState *bs, BdrvChild *c,
     }
 }
 
+void bdrv_default_perms(BlockDriverState *bs, BdrvChild *c,
+                        const BdrvChildClass *child_class, BdrvChildRole role,
+                        BlockReopenQueue *reopen_queue,
+                        uint64_t perm, uint64_t shared,
+                        uint64_t *nperm, uint64_t *nshared)
+{
+    assert(child_class == &child_of_bds);
+
+    if (role & BDRV_CHILD_FILTERED) {
+        assert(!(role & (BDRV_CHILD_DATA | BDRV_CHILD_METADATA |
+                         BDRV_CHILD_COW)));
+        bdrv_filter_default_perms(bs, c, child_class, role, reopen_queue,
+                                  perm, shared, nperm, nshared);
+    } else if (role & BDRV_CHILD_COW) {
+        assert(!(role & (BDRV_CHILD_DATA | BDRV_CHILD_METADATA)));
+        bdrv_default_perms_for_cow(bs, c, child_class, role, reopen_queue,
+                                   perm, shared, nperm, nshared);
+    } else if (role & (BDRV_CHILD_METADATA | BDRV_CHILD_DATA)) {
+        bdrv_default_perms_for_storage(bs, c, child_class, role, reopen_queue,
+                                       perm, shared, nperm, nshared);
+    } else {
+        g_assert_not_reached();
+    }
+}
+
 uint64_t bdrv_qapi_perm_to_blk_perm(BlockPermission qapi_perm)
 {
     static const uint64_t permissions[] = {

include/block/block_int.h

@@ -1288,6 +1288,17 @@ void bdrv_format_default_perms(BlockDriverState *bs, BdrvChild *c,
 bool bdrv_recurse_can_replace(BlockDriverState *bs,
                               BlockDriverState *to_replace);
 
+/*
+ * Default implementation for BlockDriver.bdrv_child_perm() that can
+ * be used by block filters and image formats, as long as they use the
+ * child_of_bds child class and set an appropriate BdrvChildRole.
+ */
+void bdrv_default_perms(BlockDriverState *bs, BdrvChild *c,
+                        const BdrvChildClass *child_class, BdrvChildRole role,
+                        BlockReopenQueue *reopen_queue,
+                        uint64_t perm, uint64_t shared,
+                        uint64_t *nperm, uint64_t *nshared);
+
 /*
  * Default implementation for drivers to pass bdrv_co_block_status() to
  * their file.