Re: [PATCH v7 12/47] block: Use bdrv_filter_(bs|child) where obvious

[Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>]

On 25.06.2020 18:21, Max Reitz wrote:
> Places that use patterns like
>
>      if (bs->drv->is_filter && bs->file) {
>          ... something about bs->file->bs ...
>      }
>
> should be
>
>      BlockDriverState *filtered = bdrv_filter_bs(bs);
>      if (filtered) {
>          ... something about @filtered ...
>      }
>
> instead.
>
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>   block.c                        | 31 ++++++++++++++++++++-----------
>   block/io.c                     |  7 +++++--
>   migration/block-dirty-bitmap.c |  8 +-------
>   3 files changed, 26 insertions(+), 20 deletions(-)
>
...
> diff --git a/block/io.c b/block/io.c
> index df8f2a98d4..385176b331 100644
> --- a/block/io.c
> +++ b/block/io.c
> @@ -3307,6 +3307,7 @@ int coroutine_fn bdrv_co_truncate(BdrvChild *child, int64_t offset, bool exact,
>                                     Error **errp)
>   {
>       BlockDriverState *bs = child->bs;
> +    BdrvChild *filtered;
>       BlockDriver *drv = bs->drv;
>       BdrvTrackedRequest req;
>       int64_t old_size, new_bytes;
> @@ -3358,6 +3359,8 @@ int coroutine_fn bdrv_co_truncate(BdrvChild *child, int64_t offset, bool exact,
>           goto out;
>       }
>   
> +    filtered = bdrv_filter_child(bs);
> +

Isn't better to have this initialization right before the relevant 
if/else block?

Andrey

>       /*
>        * If the image has a backing file that is large enough that it would
>        * provide data for the new area, we cannot leave it unallocated because
> @@ -3390,8 +3393,8 @@ int coroutine_fn bdrv_co_truncate(BdrvChild *child, int64_t offset, bool exact,
>               goto out;
>           }
>           ret = drv->bdrv_co_truncate(bs, offset, exact, prealloc, flags, errp);
> -    } else if (bs->file && drv->is_filter) {
> -        ret = bdrv_co_truncate(bs->file, offset, exact, prealloc, flags, errp);
> +    } else if (filtered) {
> +        ret = bdrv_co_truncate(filtered, offset, exact, prealloc, flags, errp);
>       } else {
>           error_setg(errp, "Image format driver does not support resize");
>           ret = -ENOTSUP;

...

Reviewed-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>