commit 3e8c2e57056614933fc5eb022e1d6d0f28071b44
author Alberto Garcia <berto@igalia.com> Mon Oct 26 14:27:15 2015 +0200
committer Kevin Wolf <kwolf@redhat.com> Wed Nov 11 16:25:47 2015 +0100
tree 2a3b6968a1406c4ac4c0e096dcaf7f9c2ab562b9
parent a911e6ae7ce47d51b519d462c1d99d53b37b0f8c

block: support passing 'backing': '' to 'blockdev-add'

Passing an empty string allows opening an image but not its backing
file. This was already described in the API documentation, only the
implementation was missing.

This is useful for creating snapshots using images opened with
blockdev-add, since they are not supposed to have a backing image
before the operation.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Jeff Cody <jcody@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block.c

diff --git a/block.c b/block.c
index a99e6d8..3493501 100644
--- a/block.c
+++ b/block.c
@@ -1393,6 +1393,7 @@
     BlockDriverState *bs;
     BlockDriver *drv = NULL;
     const char *drvname;
+    const char *backing;
     Error *local_err = NULL;
     int snapshot_flags = 0;
 
@@ -1460,6 +1461,12 @@
 
     assert(drvname || !(flags & BDRV_O_PROTOCOL));
 
+    backing = qdict_get_try_str(options, "backing");
+    if (backing && *backing == '\0') {
+        flags |= BDRV_O_NO_BACKING;
+        qdict_del(options, "backing");
+    }
+
     bs->open_flags = flags;
     bs->options = options;
     options = qdict_clone_shallow(options);