Re: [Qemu-devel] [PATCH v6 22/42] block: Fix bdrv_get_allocated_file_size's fallback

[Vladimir Sementsov-Ogievskiy]

09.08.2019 19:13, Max Reitz wrote:
> If the driver does not implement bdrv_get_allocated_file_size(), we
> should fall back to cumulating the allocated size of all non-COW
> children instead of just bs->file.
> 
> Suggested-by: Vladimir Sementsov-Ogievskiy <address@hidden>
> Signed-off-by: Max Reitz <address@hidden>
> ---
>   block.c | 22 ++++++++++++++++++++--
>   1 file changed, 20 insertions(+), 2 deletions(-)
> 
> diff --git a/block.c b/block.c
> index 1070aa1ba9..6e1ddab056 100644
> --- a/block.c
> +++ b/block.c
> @@ -4650,9 +4650,27 @@ int64_t bdrv_get_allocated_file_size(BlockDriverState 
> *bs)
>       if (drv->bdrv_get_allocated_file_size) {
>           return drv->bdrv_get_allocated_file_size(bs);
>       }
> -    if (bs->file) {
> -        return bdrv_get_allocated_file_size(bs->file->bs);
> +
> +    if (!QLIST_EMPTY(&bs->children)) {
> +        BdrvChild *child;
> +        int64_t child_size, total_size = 0;
> +
> +        QLIST_FOREACH(child, &bs->children, next) {
> +            if (child == bdrv_filtered_cow_child(bs)) {
> +                /* Ignore COW backing files */
> +                continue;
> +            }
> +
> +            child_size = bdrv_get_allocated_file_size(child->bs);
> +            if (child_size < 0) {
> +                return child_size;
> +            }
> +            total_size += child_size;
> +        }
> +
> +        return total_size;
>       }
> +
>       return -ENOTSUP;
>   }
>   
> 

Hmm..

1. No children -> -ENOTSUP
2. Only cow child -> 0
3. Some non-cow children -> SUM

It's all arguable (the strictest way is -ENOTSUP in either case),
but if we want to fallback to SUM of non-cow children, 1. and 2. should return
the same.

-- 
Best regards,
Vladimir