Re: [PATCH] rbd: cast snap_count to size_t to avoid tautological comparison warning

[Alex Elder]

On 5/28/26 3:21 PM, Rosen Penev wrote:
> snap_count is u32 but the comparison is against a SIZE_MAX-derived value
> (~2^61 on 64-bit), which clang flags as always false with
> -Wtautological-constant-out-of-range-compare. Cast to size_t so the
> comparison is done in the correct width.
>
> Assisted-by: Opencode:Big-pickle
> Signed-off-by: Rosen Penev <rosenp@xxxxxxxxx>

This is a simple fix.

You might consider doing something similar for this code in
rbd_dev_ondisk_valid():

        snap_count = le32_to_cpu(ondisk->snap_count);
        size = SIZE_MAX - sizeof (struct ceph_snap_context);
        if (snap_count > size / sizeof (__le64))
                return false;

Reviewed-by: Alex Elder <elder@xxxxxxxxxxxx>


> ---
>   drivers/block/rbd.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
> index 94709466ad19..b4ba51db9a28 100644
> --- a/drivers/block/rbd.c
> +++ b/drivers/block/rbd.c
> @@ -6079,7 +6079,7 @@ static int rbd_dev_v2_snap_context(struct rbd_device *rbd_dev,
>   	 * make sure the computed size of the snapshot context we
>   	 * allocate is representable in a size_t.
>   	 */
> -	if (snap_count > (SIZE_MAX - sizeof (struct ceph_snap_context))
> +	if ((size_t)snap_count > (SIZE_MAX - sizeof (struct ceph_snap_context))
>   				 / sizeof (u64)) {
>   		ret = -EINVAL;
>   		goto out;