block: Handle permission errors in change_parent_backing_link()
Instead of just trying to change parents by parent over to reference @to
instead of @from, and abort()ing whenever the permissions don't allow
this, do proper permission checking beforehand and pass any error to the
callers.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
diff --git a/block.c b/block.c
index a7b09d3..a310132 100644
--- a/block.c
+++ b/block.c
@@ -2933,21 +2933,53 @@
}
static void change_parent_backing_link(BlockDriverState *from,
- BlockDriverState *to)
+ BlockDriverState *to, Error **errp)
{
BdrvChild *c, *next;
+ GSList *list = NULL, *p;
+ uint64_t old_perm, old_shared;
+ uint64_t perm = 0, shared = BLK_PERM_ALL;
+ int ret;
+ /* Make sure that @from doesn't go away until we have successfully attached
+ * all of its parents to @to. */
+ bdrv_ref(from);
+
+ /* Put all parents into @list and calculate their cumulative permissions */
QLIST_FOREACH_SAFE(c, &from->parents, next_parent, next) {
if (!should_update_child(c, to)) {
continue;
}
+ list = g_slist_prepend(list, c);
+ perm |= c->perm;
+ shared &= c->shared_perm;
+ }
+
+ /* Check whether the required permissions can be granted on @to, ignoring
+ * all BdrvChild in @list so that they can't block themselves. */
+ ret = bdrv_check_update_perm(to, perm, shared, list, errp);
+ if (ret < 0) {
+ bdrv_abort_perm_update(to);
+ goto out;
+ }
+
+ /* Now actually perform the change. We performed the permission check for
+ * all elements of @list at once, so set the permissions all at once at the
+ * very end. */
+ for (p = list; p != NULL; p = p->next) {
+ c = p->data;
bdrv_ref(to);
- /* FIXME Are we sure that bdrv_replace_child() can't run into
- * &error_abort because of permissions? */
- bdrv_replace_child(c, to, true);
+ bdrv_replace_child_noperm(c, to);
bdrv_unref(from);
}
+
+ bdrv_get_cumulative_perm(to, &old_perm, &old_shared);
+ bdrv_set_perm(to, old_perm | perm, old_shared | shared);
+
+out:
+ g_slist_free(list);
+ bdrv_unref(from);
}
/*
@@ -2980,7 +3012,12 @@
goto out;
}
- change_parent_backing_link(bs_top, bs_new);
+ change_parent_backing_link(bs_top, bs_new, &local_err);
+ if (local_err) {
+ error_propagate(errp, local_err);
+ bdrv_set_backing_hd(bs_new, NULL, &error_abort);
+ goto out;
+ }
/* bs_new is now referenced by its new parents, we don't need the
* additional reference any more. */
@@ -2995,7 +3032,8 @@
bdrv_ref(old);
- change_parent_backing_link(old, new);
+ /* FIXME Proper error handling */
+ change_parent_backing_link(old, new, &error_abort);
bdrv_unref(old);
}
