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

[David Laight <david.laight.linux@gmail.com>]

On Thu, 28 May 2026 13:21:51 -0700
Rosen Penev <rosenp@gmail.com> 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.

If that warning makes any sense then the cast shouldn't make any difference.

Why not check against RBD_MAX_SNAP_COUNT - the buffer isn't big enough
to hold any more than that.

-- David

> 
> Assisted-by: Opencode:Big-pickle
> Signed-off-by: Rosen Penev <rosenp@gmail.com>
> ---
>  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;