Re: [Qemu-devel] [PATCH v10 1/9] mirror: inherit supported write/zero flags

[Anton Nefedov <anton.nefedov@virtuozzo.com>]

On 5/12/2018 3:43 PM, Vladimir Sementsov-Ogievskiy wrote:
> Could you please write, what is the behavior change and why here?
> 

The idea is that passthrough drivers should report the flags if there
are no obstacles to support it.
Technically, these changes are not connected to this series, but since
BDRV_REQ_ALLOCATE flag is added, so we might want to expose it where
possible.

> Is it a bug, that FUA was not inherited before?
> 

I don't think it's a bug really since there is a fallback path in
block/io.c.

> 03.12.2018 13:14, Anton Nefedov wrote:
>> Signed-off-by: Anton Nefedov <anton.nefedov@virtuozzo.com>
>> ---
>>    block/mirror.c | 8 ++++++--
>>    1 file changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/block/mirror.c b/block/mirror.c
>> index 56d9ef7474..56908c9b19 100644
>> --- a/block/mirror.c
>> +++ b/block/mirror.c
>> @@ -1528,8 +1528,12 @@ static void mirror_start_job(const char *job_id, BlockDriverState *bs,
>>            mirror_top_bs->implicit = true;
>>        }
>>        mirror_top_bs->total_sectors = bs->total_sectors;
>> -    mirror_top_bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED;
>> -    mirror_top_bs->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED;
>> +    mirror_top_bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED |
>> +        (BDRV_REQ_FUA & bs->supported_write_flags);
>> +    mirror_top_bs->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED |
>> +        ((BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP)
>> +         & bs->supported_zero_flags);
>> +
>>        bs_opaque = g_new0(MirrorBDSOpaque, 1);
>>        mirror_top_bs->opaque = bs_opaque;
>>        bdrv_set_aio_context(mirror_top_bs, bdrv_get_aio_context(bs));
>>
> 
>