Re: [PATCH] rbd: Use RBD fast-diff for querying actual allocation

[李义 <yilikernel@gmail.com>]

CC qemu-block and rbd maintainers

On 6/9/20, Yi Li <yili@winhong.com> wrote:
> Since Ceph version Infernalis (9.2.0) the new fast-diff mechanism
> of RBD allows for querying actual rbd image usage.
>
> Prior to this version there was no easy and fast way to query how
> much allocation a RBD image had inside a Ceph cluster.
>
> To use the fast-diff feature it needs to be enabled per RBD image
> and is only supported by Ceph cluster running version Infernalis
> (9.2.0) or newer.
>
> Without the fast-diff feature enabled qemu-img will report an allocation
> identical to the image capacity.
>
> 'qemu-img info rbd:cepharm/liyi-rbd' might output for example:
>
>   image: json:{"driver": "raw", "file": {"pool": "cepharm",
>   "image": "liyi-rbd", "driver": "rbd"}}
>   file format: raw
>   virtual size: 20 GiB (21474836480 bytes)
>   disk size: 0 B
>   cluster_size: 4194304
>
> Newly created rbds will have the fast-diff feature enabled.
>
> Signed-off-by: Yi Li <yili@winhong.com>
> ---
>  block/rbd.c | 60 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 60 insertions(+)
>
> diff --git a/block/rbd.c b/block/rbd.c
> index 617553b022..f231653f7b 100644
> --- a/block/rbd.c
> +++ b/block/rbd.c
> @@ -1107,6 +1107,65 @@ static int64_t qemu_rbd_getlength(BlockDriverState
> *bs)
>      return info.size;
>  }
>
> +#if LIBRBD_VERSION_CODE > 265
> +static int disk_usage_callback(uint64_t offset, size_t len, int exists,
> +                               void *arg)
> +{
> +  uint64_t *used_size = (uint64_t *)(arg);
> +  if (exists) {
> +    (*used_size) += len;
> +  }
> +  return 0;
> +}
> +#endif
> +
> +static int64_t qemu_rbd_allocated_file_size(BlockDriverState *bs)
> +{
> +    BDRVRBDState *s = bs->opaque;
> +    rbd_image_info_t info;
> +    int r;
> +    uint64_t used_size = 0;
> +    uint64_t features = 0;
> +
> +    r = rbd_stat(s->image, &info, sizeof(info));
> +    if (r < 0) {
> +        return r;
> +    }
> +
> +    r = rbd_get_features(s->image, &features);
> +    if (r < 0) {
> +        return r;
> +    }
> +
> +   /*
> +    * rbd_diff_iterate2() is available in versions above Ceph 0.94
> (Hammer)
> +    * It uses a object map inside Ceph which is faster than
> rbd_diff_iterate()
> +    * which iterates all objects.
> +    * LIBRBD_VERSION_CODE for Ceph 0.94 is 265. In 266 and upwards
> diff_iterate2
> +    * is available
> +    */
> +#if LIBRBD_VERSION_CODE > 265
> +    if (features & RBD_FEATURE_FAST_DIFF) {
> +
> +        /*
> +         * RBD image fast-diff feature enabled
> +         * Querying for actual allocation.
> +         */
> +        r = rbd_diff_iterate2(s->image, NULL, 0, info.size, 0, 1,
> +                              &disk_usage_callback,
> +                              &used_size);
> +        if (r < 0) {
> +            return r;
> +        }
> +    } else {
> +        used_size = info.size;
> +    }
> +#else
> +    used_size = info.size;
> +#endif
> +    return used_size;
> +}
> +
>  static int coroutine_fn qemu_rbd_co_truncate(BlockDriverState *bs,
>                                               int64_t offset,
>                                               bool exact,
> @@ -1316,6 +1375,7 @@ static BlockDriver bdrv_rbd = {
>      .bdrv_get_info          = qemu_rbd_getinfo,
>      .create_opts            = &qemu_rbd_create_opts,
>      .bdrv_getlength         = qemu_rbd_getlength,
> +    .bdrv_get_allocated_file_size = qemu_rbd_allocated_file_size,
>      .bdrv_co_truncate       = qemu_rbd_co_truncate,
>      .protocol_name          = "rbd",
>
> --
> 2.25.3
>
>
>
>