block: Make backing files child_of_bds children

Make all parents of backing files pass the appropriate BdrvChildRole.
By doing so, we can switch their BdrvChildClass over to the generic
child_of_bds, which will do the right thing when given a correct
BdrvChildRole.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200513110544.176672-24-mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 20 insertions, 6 deletions

diff --git a/block.c b/block.c
index 85b4f947ba..131ae20ffc 100644
--- a/block.c
+++ b/block.c
@@ -2942,6 +2942,20 @@ static bool bdrv_inherits_from_recursive(BlockDriverState *child,
 }
 
 /*
+ * Return the BdrvChildRole for @bs's backing child.  bs->backing is
+ * mostly used for COW backing children (role = COW), but also for
+ * filtered children (role = FILTERED | PRIMARY).
+ */
+static BdrvChildRole bdrv_backing_role(BlockDriverState *bs)
+{
+    if (bs->drv && bs->drv->is_filter) {
+        return BDRV_CHILD_FILTERED | BDRV_CHILD_PRIMARY;
+    } else {
+        return BDRV_CHILD_COW;
+    }
+}
+
+/*
  * Sets the backing file link of a BDS. A new reference is created; callers
  * which don't need their own reference any more must call bdrv_unref().
  */
@@ -2968,8 +2982,8 @@ void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd,
         goto out;
     }
 
-    bs->backing = bdrv_attach_child(bs, backing_hd, "backing", &child_backing,
-                                    0, errp);
+    bs->backing = bdrv_attach_child(bs, backing_hd, "backing", &child_of_bds,
+                                    bdrv_backing_role(bs), errp);
     /* If backing_hd was already part of bs's backing chain, and
      * inherits_from pointed recursively to bs then let's update it to
      * point directly to bs (else it will become NULL). */
@@ -3066,7 +3080,7 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict *parent_options,
     }
 
     backing_hd = bdrv_open_inherit(backing_filename, reference, options, 0, bs,
-                                   &child_backing, 0, errp);
+                                   &child_of_bds, bdrv_backing_role(bs), errp);
     if (!backing_hd) {
         bs->open_flags |= BDRV_O_NO_BACKING;
         error_prepend(errp, "Could not open backing file: ");
@@ -3895,8 +3909,8 @@ int bdrv_reopen_multiple(BlockReopenQueue *bs_queue, Error **errp)
         if (state->replace_backing_bs && state->new_backing_bs) {
             uint64_t nperm, nshared;
             bdrv_child_perm(state->bs, state->new_backing_bs,
-                            NULL, &child_backing, 0, bs_queue,
-                            state->perm, state->shared_perm,
+                            NULL, &child_of_bds, bdrv_backing_role(state->bs),
+                            bs_queue, state->perm, state->shared_perm,
                             &nperm, &nshared);
             ret = bdrv_check_update_perm(state->new_backing_bs, NULL,
                                          nperm, nshared, NULL, NULL, errp);
@@ -6852,7 +6866,7 @@ void bdrv_refresh_filename(BlockDriverState *bs)
         drv->bdrv_gather_child_options(bs, opts, backing_overridden);
     } else {
         QLIST_FOREACH(child, &bs->children, next) {
-            if (child->klass == &child_backing && !backing_overridden) {
+            if (child == bs->backing && !backing_overridden) {
                 /* We can skip the backing BDS if it has not been overridden */
                 continue;
             }