Re: [Qemu-devel] [PATCH 1/4] block: add image fragmentation statistics to qemu-img

[Stefan Hajnoczi]

On Wed, Mar 7, 2012 at 9:22 AM, Dong Xu Wang <address@hidden> wrote:
> From: Dong Xu Wang <address@hidden>
>
> Discussion can be found at:
> http://patchwork.ozlabs.org/patch/128730/
>
> This patch add image fragmentation statistics while using qemu-img info.
>
> Signed-off-by: Dong Xu Wang <address@hidden>
> ---
>  block.c     |   13 +++++++++++++
>  block.h     |    7 +++++++
>  block_int.h |    1 +
>  qemu-img.c  |    9 +++++++++
>  4 files changed, 30 insertions(+), 0 deletions(-)
>
> diff --git a/block.c b/block.c
> index 52ffe14..947607b 100644
> --- a/block.c
> +++ b/block.c
> @@ -2588,6 +2588,19 @@ int bdrv_get_info(BlockDriverState *bs, 
> BlockDriverInfo *bdi)
>     return drv->bdrv_get_info(bs, bdi);
>  }
>
> +int bdrv_get_fragment(BlockDriverState *bs, BlockFragInfo *bfi)

bdrv_get_fraginfo() makes it clearer that this function gets a summary
of fragmentation information.  bdrv_get_fragment() makes me think it
gets one specific "fragment".

> +{
> +    BlockDriver *drv = bs->drv;
> +    if (!drv) {
> +        return -ENOMEDIUM;
> +    }
> +    if (!drv->bdrv_get_fragment) {
> +        return -ENOTSUP;
> +    }
> +    memset(bfi, 0, sizeof(*bfi));
> +    return drv->bdrv_get_fragment(bs, bfi);

For now this .drv_get_fraginfo() interface makes sense but if we merge
the QCOW2<->QED in-place conversion patch series in the future it will
be possible to implement this in a generic way because image formats
will expose their guest -> host mapping.

> @@ -1126,6 +1127,14 @@ static int img_info(int argc, char **argv)
>             printf("cluster_size: %d\n", bdi.cluster_size);
>         }
>     }
> +    if (bdrv_get_fragment(bs, &bfi) >= 0) {

I think we need a separate sub-command for fragmentation info:

qemu-img fraginfo <image-file>

Utilities that invoke qemu-img info want it to be fast.  Reading all
metadata from a large image can take several seconds.  Since many
qemu-img info users don't need to see the fragmentation information,
it makes sense to put it in a new sub-command.

> +        if (bfi.total_clusters != 0 && bfi.allocated_clusters != 0) {
> +            printf("%lld/%lld = %0.2f%% allocated, %0.2f%% fragmented\n",

Please use the PRId64 macro instead of %lld because some compilers
warn when uint64_t is not typedefed to long long int.

Stefan