[Qemu-devel] [PATCH v9 07/11] block: Parse "backing" option to reference existing BDS

[Fam Zheng <famz@redhat.com>]

Now it's safe to allow reference for backing_hd in the interface.

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 block.c | 26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/block.c b/block.c
index 907c483..618b8c3 100644
--- a/block.c
+++ b/block.c
@@ -1199,12 +1199,34 @@ int bdrv_open(BlockDriverState *bs, const char *filename, QDict *options,
     /* If there is a backing file, use it */
     if ((flags & BDRV_O_NO_BACKING) == 0) {
         QDict *backing_options;
+        const char *backing_name;
+        BlockDriverState *backing_hd;
 
+        backing_name = qdict_get_try_str(options, "backing");
         qdict_extract_subqdict(options, &backing_options, "backing.");
-        ret = bdrv_open_backing_file(bs, backing_options, &local_err);
-        if (ret < 0) {
+
+        if (backing_name && qdict_size(backing_options)) {
+            error_setg(&local_err,
+                       "Option \"backing\" and \"backing.*\" cannot be "
+                       "used together");
+            ret = -EINVAL;
             goto close_and_fail;
         }
+        if (backing_name) {
+            backing_hd = bdrv_find(backing_name);
+            if (!backing_hd) {
+                error_set(&local_err, QERR_DEVICE_NOT_FOUND, backing_name);
+                ret = -ENOENT;
+                goto close_and_fail;
+            }
+            qdict_del(options, "backing");
+            bdrv_set_backing_hd(bs, backing_hd);
+        } else {
+            ret = bdrv_open_backing_file(bs, backing_options, &local_err);
+            if (ret < 0) {
+                goto close_and_fail;
+            }
+        }
     }
 
     /* Check if any unknown options were used */
-- 
1.8.5.1