Re: [Qemu-devel] [PATCHv2 1.8 7/9] qemu-img: round down request length to an aligned sector

[Paolo Bonzini <pbonzini@redhat.com>]

Il 26/11/2013 09:56, Peter Lieven ha scritto:
> this patch shortens requests to end at an aligned sector so that
> the next request starts aligned.
> 
> Signed-off-by: Peter Lieven <pl@kamp.de>
> ---
>  qemu-img.c |   30 ++++++++++++++++++++----------
>  1 file changed, 20 insertions(+), 10 deletions(-)
> 
> diff --git a/qemu-img.c b/qemu-img.c
> index b076d44..1421f0f 100644
> --- a/qemu-img.c
> +++ b/qemu-img.c
> @@ -1124,8 +1124,7 @@ out3:
>  
>  static int img_convert(int argc, char **argv)
>  {
> -    int c, n, n1, bs_n, bs_i, compress, cluster_size,
> -        cluster_sectors, skip_create;
> +    int c, n, n1, bs_n, bs_i, compress, cluster_sectors, skip_create;
>      int64_t ret = 0;
>      int progress = 0, flags;
>      const char *fmt, *out_fmt, *cache, *out_baseimg, *out_filename;
> @@ -1397,19 +1396,21 @@ static int img_convert(int argc, char **argv)
>          }
>      }
>  
> +    cluster_sectors = 0;
> +    ret = bdrv_get_info(out_bs, &bdi);
> +    if (ret < 0 && compress) {
> +        error_report("could not get block driver info");
> +        goto out;
> +    } else {
> +        cluster_sectors = bdi.cluster_size / BDRV_SECTOR_SIZE;
> +    }
> +
>      if (compress) {
> -        ret = bdrv_get_info(out_bs, &bdi);
> -        if (ret < 0) {
> -            error_report("could not get block driver info");
> -            goto out;
> -        }
> -        cluster_size = bdi.cluster_size;
> -        if (cluster_size <= 0 || cluster_size > bufsectors * BDRV_SECTOR_SIZE) {
> +        if (cluster_sectors <= 0 || cluster_sectors > bufsectors) {
>              error_report("invalid cluster size");
>              ret = -1;
>              goto out;
>          }
> -        cluster_sectors = cluster_size >> 9;
>          sector_num = 0;
>  
>          nb_sectors = total_sectors;
> @@ -1547,6 +1548,15 @@ static int img_convert(int argc, char **argv)
>                  n = nb_sectors;
>              }
>  
> +            /* round down request length to an aligned sector */

If you have to respin, /* do not bother doing this on short requests.
They happen when we found an all-zero area, and the next sector to write
will not be sector_num + n.  */

> +            if (cluster_sectors > 0 && n >= cluster_sectors) {
> +                int64_t next_aligned_sector = (sector_num + n);
> +                next_aligned_sector -= next_aligned_sector % cluster_sectors;
> +                if (sector_num + n > next_aligned_sector) {
> +                    n = next_aligned_sector - sector_num;
> +                }
> +            }
> +
>              if (n > bs_offset + bs_sectors - sector_num) {
>                  n = bs_offset + bs_sectors - sector_num;
>              }
> 

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>