[Qemu-devel] [PATCH v8 08/12] 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, 19 insertions(+), 7 deletions(-)

diff --git a/block.c b/block.c
index b3993d7..fba7148 100644
--- a/block.c
+++ b/block.c
@@ -1191,11 +1191,25 @@ 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;
-
-        qdict_extract_subqdict(options, &backing_options, "backing.");
-        ret = bdrv_open_backing_file(bs, backing_options, &local_err);
-        if (ret < 0) {
-            goto close_and_fail;
+        const char *backing_name;
+        BlockDriverState *backing_hd;
+
+        backing_name = qdict_get_try_str(options, "backing");
+        qdict_del(options, "backing");
+        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;
+            }
+            bdrv_set_backing_hd(bs, backing_hd);
+        } else {
+            qdict_extract_subqdict(options, &backing_options, "backing.");
+            ret = bdrv_open_backing_file(bs, backing_options, &local_err);
+            if (ret < 0) {
+                goto close_and_fail;
+            }
         }
     }
 
@@ -1682,7 +1696,6 @@ void bdrv_swap(BlockDriverState *bs_new, BlockDriverState *bs_old)
     assert(QLIST_EMPTY(&bs_new->dirty_bitmaps));
     assert(bs_new->job == NULL);
     assert(bs_new->dev == NULL);
-    assert(bdrv_op_blocker_is_empty(bs_new));
     assert(bs_new->io_limits_enabled == false);
     assert(!throttle_have_timer(&bs_new->throttle_state));
 
@@ -1701,7 +1714,6 @@ void bdrv_swap(BlockDriverState *bs_new, BlockDriverState *bs_old)
     /* Check a few fields that should remain attached to the device */
     assert(bs_new->dev == NULL);
     assert(bs_new->job == NULL);
-    assert(bdrv_op_blocker_is_empty(bs_new));
     assert(bs_new->io_limits_enabled == false);
     assert(!throttle_have_timer(&bs_new->throttle_state));
 
-- 
1.8.5.1