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

[Max Reitz <mreitz@redhat.com>]

On 07.04.2014 21:10, Eric Blake wrote:
> 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 <mreitz@redhat.com>
>> ---
>>   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.

Sounds interesting, I'll have a look.

>> +
>> +    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)'.

Okay, seems like I missed something.

Max

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