Re: [Qemu-devel] [PATCH 08/12] qemu-img: conditionally zero out target on convert

[Paolo Bonzini <pbonzini@redhat.com>]

Il 13/09/2013 12:25, Peter Lieven ha scritto:
> if the target has_zero_init = 0, but supports efficiently
> writing zeroes by unmapping we call bdrv_zeroize to
> avoid fully allocating the target. this currently
> is designed especially for iscsi.
> 
> Signed-off-by: Peter Lieven <pl@kamp.de>
> ---
>  qemu-img.c |   22 ++++++++++++++++------
>  1 file changed, 16 insertions(+), 6 deletions(-)
> 
> diff --git a/qemu-img.c b/qemu-img.c
> index 3e5e388..6eaddc6 100644
> --- a/qemu-img.c
> +++ b/qemu-img.c
> @@ -1354,7 +1354,8 @@ static int img_convert(int argc, char **argv)
>          }
>      }
>  
> -    flags = BDRV_O_RDWR;
> +    flags = BDRV_O_RDWR | BDRV_O_UNMAP;

I think this should be a new command-line flag.

Paolo

> +
>      ret = bdrv_parse_cache_flags(cache, &flags);
>      if (ret < 0) {
>          error_report("Invalid cache option: %s", cache);
> @@ -1386,12 +1387,13 @@ static int img_convert(int argc, char **argv)
>          }
>      }
>  
> +    ret = bdrv_get_info(out_bs, &bdi);
> +    if (ret < 0) {
> +        error_report("could not get block driver info");
> +        goto out;
> +    }
> +
>      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 > IO_BUF_SIZE) {
>              error_report("invalid cluster size");
> @@ -1470,6 +1472,14 @@ static int img_convert(int argc, char **argv)
>      } else {
>          int has_zero_init = bdrv_has_zero_init(out_bs);
>  
> +        if (!has_zero_init && !out_baseimg && bdi.discard_write_zeroes) {
> +            ret = bdrv_zeroize(out_bs, BDRV_REQ_MAY_UNMAP);
> +            if (ret < 0) {
> +                goto out;
> +            }
> +            has_zero_init = 1;
> +        }
> +
>          sector_num = 0; // total number of sectors converted so far
>          nb_sectors = total_sectors - sector_num;
>          if (nb_sectors != 0) {
>