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

[Max Reitz]

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.)

Max

> +            if (base_unfiltered->drv) {
> +                base_fmt = base_unfiltered->drv->format_name;
>              }
>          }
>          bdrv_set_backing_hd(unfiltered_bs, base, &local_err);
>

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