Re: [Qemu-devel] [PATCH v2 06/20] block: make bdrv_co_do_write_zeroes stricter in producing aligned requests

[Stefan Hajnoczi]

On Tue, Nov 19, 2013 at 06:07:29PM +0100, Paolo Bonzini wrote:
> @@ -2761,14 +2761,19 @@ static int coroutine_fn 
> bdrv_co_do_write_zeroes(BlockDriverState *bs,
>      while (nb_sectors > 0 && !ret) {
>          int num = nb_sectors;
>  
> -        /* align request */
> -        if (bs->bl.write_zeroes_alignment &&
> -            num >= bs->bl.write_zeroes_alignment &&
> -            sector_num % bs->bl.write_zeroes_alignment) {
> -            if (num > bs->bl.write_zeroes_alignment) {
> +        /* Align request.  Block drivers can expect the "bulk" of the request
> +         * to be aligned.
> +         */
> +        if (bs->bl.write_zeroes_alignment
> +            && num > bs->bl.write_zeroes_alignment) {

Here '>' is used...

> +            if (sector_num % bs->bl.write_zeroes_alignment != 0) {
> +                /* Make a small request up to the first aligned sector.  */
>                  num = bs->bl.write_zeroes_alignment;
> +                num -= sector_num % bs->bl.write_zeroes_alignment;
> +            } else if (num >= bs->bl.write_zeroes_alignment) {

...but here '>=' is used.

The == case here cannot happen.  Did you mean '>=' in both places?