Re: [Qemu-devel] [PATCHv3 08/20] block: honour BlockLimits in bdrv_co_discard

[Stefan Hajnoczi]

On Tue, Sep 24, 2013 at 03:35:02PM +0200, Peter Lieven wrote:
> @@ -4245,7 +4250,37 @@ int coroutine_fn bdrv_co_discard(BlockDriverState *bs, 
> int64_t sector_num,
>      }
>  
>      if (bs->drv->bdrv_co_discard) {
> -        return bs->drv->bdrv_co_discard(bs, sector_num, nb_sectors);
> +        int max_discard = bs->bl.max_discard ?
> +                          bs->bl.max_discard : MAX_DISCARD_DEFAULT;
> +
> +        while (nb_sectors > 0) {
> +            int ret;
> +            int num = nb_sectors;
> +
> +            /* align request */
> +            if (bs->bl.discard_alignment &&
> +                num >= bs->bl.discard_alignment &&
> +                sector_num % bs->bl.discard_alignment) {
> +                if (num > bs->bl.discard_alignment) {
> +                    num = bs->bl.discard_alignment;
> +                }
> +                num -= sector_num % bs->bl.discard_alignment;
> +            }

Is it always possible to discard at arbitrary sector offsets?