Re: [PATCH v1 1/1] ceph: Amend checking to fix `make W=1` build breakage

[Viacheslav Dubeyko]

On Mon, 2025-11-10 at 15:44 +0100, Andy Shevchenko wrote:
> In a few cases the code compares 32-bit value to a SIZE_MAX derived
> constant which is much higher than that value on 64-bit platforms,
> Clang, in particular, is not happy about this
> 
> fs/ceph/snap.c:377:10: error: result of comparison of constant 2305843009213693948 with expression of type 'u32' (aka 'unsigned int') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
>   377 |         if (num > (SIZE_MAX - sizeof(*snapc)) / sizeof(u64))
>       |             ~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Fix this by casting to size_t. Note, that possible replacement of SIZE_MAX
> by U32_MAX may lead to the behaviour changes on the corner cases.
> 
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> ---
>  fs/ceph/snap.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
> index c65f2b202b2b..521507ea8260 100644
> --- a/fs/ceph/snap.c
> +++ b/fs/ceph/snap.c
> @@ -374,7 +374,7 @@ static int build_snap_context(struct ceph_mds_client *mdsc,
>  
>  	/* alloc new snap context */
>  	err = -ENOMEM;
> -	if (num > (SIZE_MAX - sizeof(*snapc)) / sizeof(u64))
> +	if ((size_t)num > (SIZE_MAX - sizeof(*snapc)) / sizeof(u64))

The same question is here. Does it makes sense to declare num as size_t? Could
it be more clean solution? Or could it introduce another warnings/errors?

Thanks,
Slava.

>  		goto fail;
>  	snapc = ceph_create_snap_context(num, GFP_NOFS);
>  	if (!snapc)