Il 17/07/2013 11:42, Fam Zheng ha scritto:
> This option allows overriding backing hd of drive. If the target drive
> exists, it's referenced as the backing file and refcount incremented.
>
> Example:
> qemu-system-x86_64 -drive \
> file.filename=foo.qcow2,if=none,id=foo \
> -drive file=bar.qcow2,backing=foo
I guess this is where we need the soft reference.
This has a _lot_ of potential for misuse, I think Kevin bashed me and
Federico very heavily when we tried to do something similar.
block/backup.c is the right place where we can override the backing hd
of the drive. Perhaps we can add a way to open a file with
BDRV_O_NO_BACKING from the command line.
Paolo
> Signed-off-by: Fam Zheng <f...@redhat.com>
> ---
> block.c | 30 ++++++++++++++++++++++++------
> 1 file changed, 24 insertions(+), 6 deletions(-)
>
> diff --git a/block.c b/block.c
> index 147a448..31fab07 100644
> --- a/block.c
> +++ b/block.c
> @@ -1083,12 +1083,30 @@ 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;
> -
> - extract_subqdict(options, &backing_options, "backing.");
> - ret = bdrv_open_backing_file(bs, backing_options);
> - if (ret < 0) {
> - goto close_and_fail;
> + const char *backing_drive;
> + backing_drive = qdict_get_try_str(options, "backing");
> + if (backing_drive) {
> + bs->backing_hd = bdrv_find(backing_drive);
> + if (bs->backing_hd) {
> + bdrv_ref(bs->backing_hd, false);
> + pstrcpy(bs->backing_file, sizeof(bs->backing_file),
> + bs->backing_hd->filename);
> + pstrcpy(bs->backing_format, sizeof(bs->backing_format),
> + bs->backing_hd->drv->format_name);
> + } else {
> + qerror_report(ERROR_CLASS_DEVICE_NOT_FOUND,
> + "Can't find drive with name %s\n", backing_drive);
> + ret = -EINVAL;
> + goto close_and_fail;
> + }
> + qdict_del(options, "backing");
> + } else {
> + QDict *backing_options;
> + extract_subqdict(options, &backing_options, "backing.");
> + ret = bdrv_open_backing_file(bs, backing_options);
> + if (ret < 0) {
> + goto close_and_fail;
> + }
> }
> }
>
>
