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block: don't add 'driver' to options when referring to backing via node name 

When referring to a backing file of an image via node name
bdrv_open_backing_file would add the 'driver' option to the option list
filling it with the backing format driver. This breaks construction of
the backing chain via -blockdev, as bdrv_open_inherit reports an error
if both 'reference' and 'options' are provided.

$ qemu-img create -f raw /tmp/backing.raw 64M
$ qemu-img create -f qcow2 -F raw -b /tmp/backing.raw /tmp/test.qcow2
$ qemu-system-x86_64 \
  -blockdev driver=file,filename=/tmp/backing.raw,node-name=backing \
  -blockdev driver=qcow2,file.driver=file,file.filename=/tmp/test.qcow2,node-name=root,backing=backing
qemu-system-x86_64: -blockdev driver=qcow2,file.driver=file,file.filename=/tmp/test.qcow2,node-name=root,backing=backing: Could not open backing file: Cannot reference an existing block device with additional options or a new filename

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Peter Krempa 2017-10-12 16:14:10 +02:00 committed by Kevin Wolf
parent ae49fbbcd8
commit 6bff597bf6
1 changed files with 2 additions and 1 deletions
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3
block.c
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@ -2245,7 +2245,8 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict *parent_options,
goto free_exit;
}
if (bs->backing_format[0] != '\0' && !qdict_haskey(options, "driver")) {
if (!reference &&
bs->backing_format[0] != '\0' && !qdict_haskey(options, "driver")) {
qdict_put_str(options, "driver", bs->backing_format);
}