Re: [PATCH v4 22/30] qcow2: Fix offset calculation in handle_dependencies()

[Vladimir Sementsov-Ogievskiy]

17.03.2020 21:16, Alberto Garcia wrote:
> l2meta_cow_start() and l2meta_cow_end() are not necessarily
> cluster-aligned if the image has subclusters, so update the
> calculation of old_start and old_end to guarantee that no two requests
> try to write on the same cluster.
>
> Signed-off-by: Alberto Garcia <address@hidden>
> Reviewed-by: Max Reitz <address@hidden>

Somehow, this patch say me "hey, there may be a lot of other small places, which we 
forget to fix about subclusters, and you have no idea, how to find and check them 
all" :) Probably the only way is reviewing the whole qcow2 code, but it's too huge 
task.. [this is just thinking out loud]

Actually, you call it "Fix", and it seems to be a fix for your "[PATCH v4 17/30] 
qcow2: Add subcluster support to calculate_l2_meta()". Shouldn't it be squashed in?

> ---
>   block/qcow2-cluster.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
> index 824c710760..ceacd91ea3 100644
> --- a/block/qcow2-cluster.c
> +++ b/block/qcow2-cluster.c
> @@ -1306,8 +1306,8 @@ static int handle_dependencies(BlockDriverState *bs, 
> uint64_t guest_offset,
>   
>           uint64_t start = guest_offset;
>           uint64_t end = start + bytes;
> -        uint64_t old_start = l2meta_cow_start(old_alloc);
> -        uint64_t old_end = l2meta_cow_end(old_alloc);
> +        uint64_t old_start = start_of_cluster(s, l2meta_cow_start(old_alloc));
> +        uint64_t old_end = ROUND_UP(l2meta_cow_end(old_alloc), 
> s->cluster_size);
>   
>           if (end <= old_start || start >= old_end) {
>               /* No intersection */


--
Best regards,
Vladimir