Re: [PATCH v3 2/2] quorum: Implement bdrv_co_pwrite_zeroes()

[Max Reitz <mreitz@redhat.com>]

On 13.11.20 17:07, Alberto Garcia wrote:
> On Fri 13 Nov 2020 12:49:04 PM CET, Max Reitz wrote:
>> On 11.11.20 17:53, Alberto Garcia wrote:
>>> This simply calls bdrv_co_pwrite_zeroes() in all children
>>>
>>> Signed-off-by: Alberto Garcia <berto@igalia.com>
>>> ---
>>>    block/quorum.c             | 18 ++++++++++++++++--
>>>    tests/qemu-iotests/312     |  7 +++++++
>>>    tests/qemu-iotests/312.out |  4 ++++
>>>    3 files changed, 27 insertions(+), 2 deletions(-)
>>
>> Should we set supported_zero_flags to something?  I think we can at
>> least set BDRV_REQ_NO_FALLBACK.  We could also try BDRV_REQ_FUA.
> 
> We could set all supported_zero_flags as long as all children support
> them, right?

Sure, I was just thinking that we could set these regardless of whether 
the children support them, because (on zero-writes) the block layer will 
figure out for us whether the child nodes support them. O:)

>>> +    if (acb->flags & BDRV_REQ_ZERO_WRITE) {
>>> +        sacb->ret = bdrv_co_pwrite_zeroes(s->children[i], acb->offset,
>>> +                                          acb->bytes, acb->flags);
>>> +    } else {
>>> +        sacb->ret = bdrv_co_pwritev(s->children[i], acb->offset, acb->bytes,
>>> +                                    acb->qiov, acb->flags);
>>> +    }
>>
>> Seems unnecessary (bdrv_co_pwritev() can handle BDRV_REQ_ZERO_WRITE),
>> but perhaps it’s good to be explicit.
> 
> pwrite_zeroes() does this additionaly:
> 
>      if (!(child->bs->open_flags & BDRV_O_UNMAP)) {
>          flags &= ~BDRV_REQ_MAY_UNMAP;
>      }

Interesting.  Technically, Quorum doesn’t support that flag (in 
supported_zero_flags O:))), so it shouldn’t appear, but, er, well then.

Max