Re: [PATCH v4 1/2] qcow2: Report BDRV_BLOCK_ZERO more accurately in bdrv_co_block_status()

[Vladimir Sementsov-Ogievskiy]

21.09.2020 17:30, Alberto Garcia wrote:
> If a BlockDriverState supports backing files but has none then any
> unallocated area reads back as zeroes.
>
> bdrv_co_block_status() is only reporting this is if want_zero is true,
> but this is an inexpensive test and there is no reason not to do it in
> all cases.
>
> Suggested-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> Signed-off-by: Alberto Garcia <berto@igalia.com>

Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

> ---
>   block/io.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/block/io.c b/block/io.c
> index a2389bb38c..ef1ea806e8 100644
> --- a/block/io.c
> +++ b/block/io.c
> @@ -2391,17 +2391,17 @@ static int coroutine_fn 
> bdrv_co_block_status(BlockDriverState *bs,
>   
>       if (ret & (BDRV_BLOCK_DATA | BDRV_BLOCK_ZERO)) {
>           ret |= BDRV_BLOCK_ALLOCATED;
> -    } else if (want_zero && bs->drv->supports_backing) {
> +    } else if (bs->drv->supports_backing) {
>           BlockDriverState *cow_bs = bdrv_cow_bs(bs);
>   
> -        if (cow_bs) {
> +        if (!cow_bs) {
> +            ret |= BDRV_BLOCK_ZERO;
> +        } else if (want_zero) {
>               int64_t size2 = bdrv_getlength(cow_bs);
>   
>               if (size2 >= 0 && offset >= size2) {
>                   ret |= BDRV_BLOCK_ZERO;
>               }
> -        } else {
> -            ret |= BDRV_BLOCK_ZERO;
>           }
>       }
>   


--
Best regards,
Vladimir