Re: [PATCH 3/9] rbd: avoid out-of-range warning

[Xiubo Li]

On 3/28/24 22:53, Alex Elder wrote:
> On 3/28/24 9:30 AM, Arnd Bergmann wrote:
> > From: Arnd Bergmann <arnd@xxxxxxxx>
> >
> > clang-14 points out that the range check is always true on 64-bit
> > architectures since a u32 is not greater than the allowed size:
> >
> > drivers/block/rbd.c:6079:17: 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]
> w
> >              ~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >
> > This is harmless, so just change the type of the temporary to size_t
> > to shut up that warning.
>
> This fixes the warning, but then the now size_t value is passed
> to ceph_decode_32_safe(), which implies a different type conversion.
> That too is not harmful, but...
>
> Could we just cast the value in the comparison instead?
>
>   if ((size_t)snap_count > (SIZE_MAX - sizeof (struct ceph_snap_context))
>
> You could drop the space between sizeof and ( while
> you're at it (I always used the space back then).
Agree.

- Xiubo


> -Alex
>
> > Fixes: bb23e37acb2a ("rbd: refactor rbd_header_from_disk()")
> > Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> > ---
> >   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 26ff5cd2bf0a..cb25ee513ada 100644
> > --- a/drivers/block/rbd.c
> > +++ b/drivers/block/rbd.c
> > @@ -6062,7 +6062,7 @@ static int rbd_dev_v2_snap_context(struct 
> > rbd_device *rbd_dev,
> >       void *p;
> >       void *end;
> >       u64 seq;
> > -    u32 snap_count;
> > +    size_t snap_count;
> >       struct ceph_snap_context *snapc;
> >       u32 i;