Re: [Qemu-devel] [PATCH 2/2] block: resize backing image during active layer commit, if needed

[Fam Zheng <famz@redhat.com>]

On Mon, 01/13 15:18, Jeff Cody wrote:
> If the top image to commit is the active layer, and also larger than
> the base image, then an I/O error will likely be returned during
> block-commit.
> 
> For instance, if we have a base image with a virtual size 10G, and a
> active layer image of size 20G, then committing the snapshot via
> 'block-commit' will likely fail.
> 
> This will automatically attempt to resize the base image, if the
> active layer image to be committed is larger.
> 
> Signed-off-by: Jeff Cody <jcody@redhat.com>
> ---
>  block/mirror.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/block/mirror.c b/block/mirror.c
> index 2932bab..c4e42fa 100644
> --- a/block/mirror.c
> +++ b/block/mirror.c
> @@ -630,9 +630,22 @@ void commit_active_start(BlockDriverState *bs, BlockDriverState *base,
>                           BlockDriverCompletionFunc *cb,
>                           void *opaque, Error **errp)
>  {
> +    int64_t length;
>      if (bdrv_reopen(base, bs->open_flags, errp)) {
>          return;
>      }

"base" is already reopened here.

> +
> +    length = bdrv_getlength(bs);
> +
> +    if (length > bdrv_getlength(base)) {
> +        if (bdrv_truncate(base, length) < 0) {
> +            error_setg(errp, "Top image %s is larger than base image %s, and "
> +                             "resize of base image failed.",
> +                             bs->filename, base->filename);
> +            return;

Should we restore open flags for base?

Thanks,
Fam

> +        }
> +    }
> +
>      bdrv_ref(base);
>      mirror_start_job(bs, base, speed, 0, 0,
>                       on_error, on_error, cb, opaque, errp,
> -- 
> 1.8.3.1
>