Re: [Qemu-block] [PATCH v4 1/4] block: pass bdrv_* methods to bs->file by default in block filters

[Eric Blake]

On 07/11/2017 11:37 AM, Manos Pitsidianakis wrote:
> The following functions fail if bs->drv is a filter and does not
> implement them:
> 
> bdrv_probe_blocksizes
> bdrv_probe_geometry
> bdrv_truncate
> bdrv_has_zero_init
> bdrv_get_info
> 
> Instead, the call should be passed to bs->file if it exists, to allow
> filter drivers to support those methods without implementing them. This
> commit makes `drv->is_filter = true` imply that these callbacks will be
> forwarded to bs->file by default, so disabling support for these
> functions must be done explicitly.
> 
> Signed-off-by: Manos Pitsidianakis <address@hidden>
> ---
>  block.c                   | 21 +++++++++++++++++++--
>  include/block/block_int.h |  6 +++++-
>  2 files changed, 24 insertions(+), 3 deletions(-)
> @@ -3778,6 +3786,9 @@ int bdrv_has_zero_init(BlockDriverState *bs)
>      if (bs->drv->bdrv_has_zero_init) {
>          return bs->drv->bdrv_has_zero_init(bs);
>      }
> +    if (bs->file && bs->drv->is_filter) {
> +        return bdrv_has_zero_init(bs->file->bs);
> +    }
>  
>      /* safe default */
>      return 0;

Someday, we should probably clean this function (and all callback
implementations) to return bool rather than int.  But not this patch.

Certainly more conservative than the earlier versions.  I'd still trust
Kevin's review over mine, but looks okay to me.

Reviewed-by: Eric Blake <address@hidden>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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