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

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

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