[Qemu-devel] [PATCH V9 3/4] block: Add backing file loop check in change_backing_file()

[Xu Wang <gesaint@linux.vnet.ibm.com>]

Backing file loop should be checked before calling change_backing_
file(). If loop appeared, this calling should be stopped and an
error printed.

Signed-off-by: Xu Wang <gesaint@linux.vnet.ibm.com>
---
 block.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/block.c b/block.c
index b8cea1c..87f7018 100644
--- a/block.c
+++ b/block.c
@@ -2075,6 +2075,7 @@ static void coroutine_fn wait_for_overlapping_requests(BlockDriverState *bs,
  * Return values:
  * 0        - success
  * -EINVAL  - backing format specified, but no file
+ * -EIO     - generic I/O error (may happen for all errors)
  * -ENOSPC  - can't update the backing file because no space is left in the
  *            image file header
  * -ENOTSUP - format driver doesn't support changing the backing file
@@ -2083,6 +2084,7 @@ int bdrv_change_backing_file(BlockDriverState *bs,
     const char *backing_file, const char *backing_fmt)
 {
     BlockDriver *drv = bs->drv;
+    Error *local_err = NULL;
     int ret;
 
     /* Backing file format doesn't make sense without a backing file */
@@ -2090,6 +2092,13 @@ int bdrv_change_backing_file(BlockDriverState *bs,
         return -EINVAL;
     }
 
+    /* Check if loop exists in backing files chain after change */
+    if (!bdrv_backing_chain_okay(backing_file, NULL, bs->filename, 
+                                 &local_err)) {
+        error_report("Backing file check: %s", error_get_pretty(local_err));
+        return -EIO;
+    }
+
     if (drv->bdrv_change_backing_file != NULL) {
         ret = drv->bdrv_change_backing_file(bs, backing_file, backing_fmt);
     } else {
-- 
1.8.1.4