Re: [PATCH v11 10/13] stream: skip filters when writing backing file name to QCOW2 header

[Vladimir Sementsov-Ogievskiy]

14.10.2020 18:02, Max Reitz wrote:
> On 12.10.20 19:43, Andrey Shinkevich wrote:
> > Avoid writing a filter JSON-name to QCOW2 image when the backing file
> > is changed after the block stream job.
> >
> > Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
> > ---
> >   block/stream.c | 9 +++++----
> >   1 file changed, 5 insertions(+), 4 deletions(-)
> >
> > diff --git a/block/stream.c b/block/stream.c
> > index e0540ee..51462bd 100644
> > --- a/block/stream.c
> > +++ b/block/stream.c
> > @@ -65,6 +65,7 @@ static int stream_prepare(Job *job)
> >       BlockDriverState *bs = blk_bs(bjob->blk);
> >       BlockDriverState *unfiltered_bs = bdrv_skip_filters(bs);
> >       BlockDriverState *base = bdrv_filter_or_cow_bs(s->above_base);
> > +    BlockDriverState *base_unfiltered = bdrv_skip_filters(base);
> >       Error *local_err = NULL;
> >       int ret = 0;
> >   
> > @@ -73,10 +74,10 @@ static int stream_prepare(Job *job)
> >   
> >       if (bdrv_cow_child(unfiltered_bs)) {
> >           const char *base_id = NULL, *base_fmt = NULL;
> > -        if (base) {
> > -            base_id = s->backing_file_str;
> > -            if (base->drv) {
> > -                base_fmt = base->drv->format_name;
> > +        if (base_unfiltered) {
> > +            base_id = base_unfiltered->filename;
>
> I think you have to leave this querying s->backing_file_str, and instead
> change how qmp_block_stream() gets @base_name.  block-stream has a
> backing-file parameter that can override the string that should be used
> here.
>
> (Or perhaps you can let qmp_block_stream() just set it to NULL if no
> backing-file parameter is passed and then fall back to
> base_unfiltered->filename only here.  Probably better, actually, in case
> base_unfiltered is changed during the job run.)

Agree with the way in brackets.

If user set backing-file parameter we should handle it here.

If backing-file is not set, we should use dynamically calculated unfiltered 
base in stream_prepare().

--
Best regards,
Vladimir