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

[Alex Elder <elder@ieee.org>]

On 5/28/26 4:05 PM, David Laight wrote:
> 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.

I like that better.  Please do that instead (despite my
Reviewed-by provided earlier).

					-Alex

> 
> -- 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;
> 
>