block: Add Error parameter to bdrv_set_backing_hd()

Not all callers of bdrv_set_backing_hd() know for sure that attaching
the backing file will be allowed by the permission system. Return the
error from the function rather than aborting.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Acked-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>

1 files changed, 23 insertions, 7 deletions

diff --git a/block.c b/block.c
index 74ac7dcf74..6440b61be6 100644
--- a/block.c
+++ b/block.c
@@ -1883,7 +1883,8 @@ static void bdrv_parent_cb_resize(BlockDriverState *bs)
  * 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().
  */
-void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd)
+void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd,
+                         Error **errp)
 {
     if (backing_hd) {
         bdrv_ref(backing_hd);
@@ -1897,9 +1898,12 @@ void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd)
         bs->backing = NULL;
         goto out;
     }
-    /* FIXME Error handling */
+
     bs->backing = bdrv_attach_child(bs, backing_hd, "backing", &child_backing,
-                                    &error_abort);
+                                    errp);
+    if (!bs->backing) {
+        bdrv_unref(backing_hd);
+    }
 
 out:
     bdrv_refresh_limits(bs, NULL);
@@ -1983,8 +1987,12 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict *parent_options,
 
     /* Hook up the backing file link; drop our reference, bs owns the
      * backing_hd reference now */
-    bdrv_set_backing_hd(bs, backing_hd);
+    bdrv_set_backing_hd(bs, backing_hd, &local_err);
     bdrv_unref(backing_hd);
+    if (local_err) {
+        ret = -EINVAL;
+        goto free_exit;
+    }
 
     qdict_del(parent_options, bdref_key);
 
@@ -2818,7 +2826,7 @@ static void bdrv_close(BlockDriverState *bs)
         bs->drv->bdrv_close(bs);
         bs->drv = NULL;
 
-        bdrv_set_backing_hd(bs, NULL);
+        bdrv_set_backing_hd(bs, NULL, &error_abort);
 
         if (bs->file != NULL) {
             bdrv_unref_child(bs, bs->file);
@@ -2927,7 +2935,8 @@ void bdrv_append(BlockDriverState *bs_new, BlockDriverState *bs_top)
     bdrv_ref(bs_top);
 
     change_parent_backing_link(bs_top, bs_new);
-    bdrv_set_backing_hd(bs_new, bs_top);
+    /* FIXME Error handling */
+    bdrv_set_backing_hd(bs_new, bs_top, &error_abort);
     bdrv_unref(bs_top);
 
     /* bs_new is now referenced by its new parents, we don't need the
@@ -3075,6 +3084,7 @@ int bdrv_drop_intermediate(BlockDriverState *active, BlockDriverState *top,
                            BlockDriverState *base, const char *backing_file_str)
 {
     BlockDriverState *new_top_bs = NULL;
+    Error *local_err = NULL;
     int ret = -EIO;
 
     if (!top->drv || !base->drv) {
@@ -3107,7 +3117,13 @@ int bdrv_drop_intermediate(BlockDriverState *active, BlockDriverState *top,
     if (ret) {
         goto exit;
     }
-    bdrv_set_backing_hd(new_top_bs, base);
+
+    bdrv_set_backing_hd(new_top_bs, base, &local_err);
+    if (local_err) {
+        ret = -EPERM;
+        error_report_err(local_err);
+        goto exit;
+    }
 
     ret = 0;
 exit: