Re: [Qemu-devel] [PATCH 1/2] dma-helpers: explicitly pass alignment into dma-helpers

[John Snow <jsnow@redhat.com>]

On 10/10/2016 03:23 PM, Mark Cave-Ayland wrote:
> On 10/10/16 17:34, Eric Blake wrote:
>
>> On 10/09/2016 11:43 AM, Mark Cave-Ayland wrote:
>>> The hard-coded default alignment is BDRV_SECTOR_SIZE, however this is not
>>> necessarily the case for all platforms. Use this as the default alignment for
>>> all current callers.
>>>
>>> Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
>>> ---
>>
>>> @@ -160,8 +161,8 @@ static void dma_blk_cb(void *opaque, int ret)
>>>          return;
>>>      }
>>>
>>> -    if (dbs->iov.size & ~BDRV_SECTOR_MASK) {
>>> -        qemu_iovec_discard_back(&dbs->iov, dbs->iov.size & ~BDRV_SECTOR_MASK);
>>> +    if (dbs->iov.size & (dbs->align - 1)) {
>>> +        qemu_iovec_discard_back(&dbs->iov, dbs->iov.size & (dbs->align - 1));
>>
>> Would it be any smarter to use osdep.h's QEMU_IS_ALIGNED(dbs->iov.size,
>> dbs->align) and QEMU_ALIGN_DOWN(dbs->iov.size, dbs->align)?
>> Semantically it is the same, but the macros make it obvious what the
>> bit-twiddling is doing.
>>
>> Unless you think that needs a tweak,
>> Reviewed-by: Eric Blake <eblake@redhat.com>
>
> I can't say I feel too strongly about it since there are plenty of other
> examples of this style in the codebase, so I'm happy to go with whatever
> John/Paolo are most happy with.
>
>
> ATB,
>
> Mark.
>

I can't pretend I am consistent, but when in doubt use the macro. Not 
worth a respin IMO, but I think this falls out of my jurisdiction :)

Acked-by: John Snow <jsnow@redhat.com>