Re: [PATCH v6 1/5] block/io: fix bdrv_co_block_status_above

[Alberto Garcia]

On Wed 16 Sep 2020 02:20:04 PM CEST, Vladimir Sementsov-Ogievskiy 
<vsementsov@virtuozzo.com> wrote:
> bdrv_co_block_status_above has several design problems with handling
> short backing files:
>
> 1. With want_zeros=true, it may return ret with BDRV_BLOCK_ZERO but
> without BDRV_BLOCK_ALLOCATED flag, when actually short backing file
> which produces these after-EOF zeros is inside requested backing
> sequence.
>
> 2. With want_zero=false, it may return pnum=0 prior to actual EOF,
> because of EOF of short backing file.
>
> Fix these things, making logic about short backing files clearer.
>
> With fixed bdrv_block_status_above we also have to improve is_zero in
> qcow2 code, otherwise iotest 154 will fail, because with this patch we
> stop to merge zeros of different types (produced by fully unallocated
> in the whole backing chain regions vs produced by short backing files).
>
> Note also, that this patch leaves for another day the general problem
> around block-status: misuse of BDRV_BLOCK_ALLOCATED as is-fs-allocated
> vs go-to-backing.
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

Reviewed-by: Alberto Garcia <berto@igalia.com>

Berto