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

[Eric Blake <eblake@redhat.com>]

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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>

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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