blockdev: Allow creation of BDS trees without BB

If the "id" field is missing from the options given to blockdev-add,
just omit the BlockBackend and create the BlockDriverState tree alone.

However, if "id" is missing, "node-name" must be specified; otherwise,
the BDS tree would no longer be accessible.

Many BDS options which are not parsed by bdrv_open() (like caching)
cannot be specified for these BB-less BDS trees yet. A future patch will
remove this limitation.

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

2 files changed, 3 insertions, 3 deletions

diff --git a/tests/qemu-iotests/087 b/tests/qemu-iotests/087
index 8694749947..af44299e07 100755
--- a/tests/qemu-iotests/087
+++ b/tests/qemu-iotests/087
@@ -54,7 +54,7 @@ size=128M
 _make_test_img $size
 
 echo
-echo === Missing ID ===
+echo === Missing ID and node-name ===
 echo
 
 run_qemu <<EOF
diff --git a/tests/qemu-iotests/087.out b/tests/qemu-iotests/087.out
index c509a408e2..7d62cd5840 100644
--- a/tests/qemu-iotests/087.out
+++ b/tests/qemu-iotests/087.out
@@ -1,12 +1,12 @@
 QA output created by 087
 Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728
 
-=== Missing ID ===
+=== Missing ID and node-name ===
 
 Testing:
 QMP_VERSION
 {"return": {}}
-{"error": {"class": "GenericError", "desc": "Block device needs an ID"}}
+{"error": {"class": "GenericError", "desc": "'id' and/or 'node-name' need to be specified for the root node"}}
 {"return": {}}
 {"timestamp": {"seconds":  TIMESTAMP, "microseconds":  TIMESTAMP}, "event": "SHUTDOWN"}