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authorJeff Cody <jcody@redhat.com>2014-06-25 15:40:10 -0400
committerStefan Hajnoczi <stefanha@redhat.com>2014-07-01 10:47:01 +0200
commit54e269009099cdc9483be115f1e12d56ad459c5e (patch)
treea7504876994f5abe0e628e5668848594b338fa98 /block.c
parent5a6684d2b957f9ec75d7ed7b14332293abec1d6c (diff)
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block: extend block-commit to accept a string for the backing file
On some image chains, QEMU may not always be able to resolve the filenames properly, when updating the backing file of an image after a block commit. For instance, certain relative pathnames may fail, or drives may have been specified originally by file descriptor (e.g. /dev/fd/???), or a relative protocol pathname may have been used. In these instances, QEMU may lack the information to be able to make the correct choice, but the user or management layer most likely does have that knowledge. With this extension to the block-commit api, the user is able to change the backing file of the overlay image as part of the block-commit operation. This allows the change to be 'safe', in the sense that if the attempt to write the overlay image metadata fails, then the block-commit operation returns failure, without disrupting the guest. If the commit top is the active layer, then specifying the backing file string will be treated as an error (there is no overlay image to modify in that case). If a backing file string is not specified in the command, the backing file string to use is determined in the same manner as it was previously. Reviewed-by: Eric Blake <eblake@redhat.com> Signed-off-by: Jeff Cody <jcody@redhat.com> Reviewed-by: Kevin Wolf <kwolf@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Diffstat (limited to 'block.c')
-rw-r--r--block.c8
1 files changed, 6 insertions, 2 deletions
diff --git a/block.c b/block.c
index f45e63c..f80e2b2 100644
--- a/block.c
+++ b/block.c
@@ -2555,12 +2555,15 @@ typedef struct BlkIntermediateStates {
*
* base <- active
*
+ * If backing_file_str is non-NULL, it will be used when modifying top's
+ * overlay image metadata.
+ *
* Error conditions:
* if active == top, that is considered an error
*
*/
int bdrv_drop_intermediate(BlockDriverState *active, BlockDriverState *top,
- BlockDriverState *base)
+ BlockDriverState *base, const char *backing_file_str)
{
BlockDriverState *intermediate;
BlockDriverState *base_bs = NULL;
@@ -2612,7 +2615,8 @@ int bdrv_drop_intermediate(BlockDriverState *active, BlockDriverState *top,
}
/* success - we can delete the intermediate states, and link top->base */
- ret = bdrv_change_backing_file(new_top_bs, base_bs->filename,
+ backing_file_str = backing_file_str ? backing_file_str : base_bs->filename;
+ ret = bdrv_change_backing_file(new_top_bs, backing_file_str,
base_bs->drv ? base_bs->drv->format_name : "");
if (ret) {
goto exit;