Re: [Qemu-devel] [PATCH 3/4] qemu-img: Implement commit like QMP

[Eric Blake]

On 04/07/2014 11:29 AM, Max Reitz wrote:
> qemu-img should use QMP commands whenever possible in order to ensure
> feature completeness of both online and offline image operations. As
> qemu-img itself has no access to QMP (since this would basically require
> just everything being linked into qemu-img), imitate QMP's
> implementation of block-commit by using commit_active_start() and then
> waiting for the block job to finish.
> 
> This new implementation does not empty the snapshot image, as opposed to
> the old implementation using bdrv_commit(). However, as QMP's
> block-commit apparently never did this and as qcow2 (which is probably
> qemu's standard image format) does not even implement the required
> function (bdrv_make_empty()), it does not seem necessary.
> 
> Signed-off-by: Max Reitz <address@hidden>
> ---
>  block/Makefile.objs |  2 +-
>  qemu-img.c          | 68 
> ++++++++++++++++++++++++++++++++++++++---------------
>  2 files changed, 50 insertions(+), 20 deletions(-)
> 

> @@ -728,29 +755,32 @@ static int img_commit(int argc, char **argv)
>      if (!bs) {
>          return 1;
>      }

> +
> +    base_bs = bdrv_find_base(bs);
> +    if (!base_bs) {
> +        error_set(&local_err, QERR_BASE_NOT_FOUND, "NULL");
> +        goto done;
> +    }

Is it worth adding an optional '-b base' image to allow qemu-img to
commit across multiple images?  That is, QMP can shorten from 'a <- b <-
c' all the way to 'a'; but qemu-img has to be called twice (once to 'a
<- b' and second to 'a').  Separate commit, of course.

> +
> +    commit_active_start(bs, base_bs, 0, COMMIT_BUF_SECTORS << 
> BDRV_SECTOR_BITS,
> +                        BLOCKDEV_ON_ERROR_REPORT, dummy_block_job_cb, bs,
> +                        &local_err);
> +    if (error_is_set(&local_err)) {

No new uses of error_is_set if we can help it.  This can be 'if
(local_err)'.

> +        goto done;
>      }
>  
> +    run_block_job(bs->job, &local_err);
> +
> +done:
>      bdrv_unref(bs);
> -    if (ret) {
> +
> +    if (error_is_set(&local_err)) {

and again.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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