Re: [PATCH 1/2] IB/hfi1: Fix a parameter of find_first_bit.

[Leon Romanovsky <leon@kernel.org>]

[-- Attachment #1: Type: text/plain, Size: 1443 bytes --]

On Fri, Aug 26, 2016 at 02:01:55PM -0400, Doug Ledford wrote:
> On 8/26/2016 9:35 AM, Doug Ledford wrote:
> > On 8/26/2016 12:49 AM, Christophe JAILLET wrote:
> >> The 2nd parameter of 'find_first_bit' is the number of bits to search.
> >> In this case, we are passing 'sizeof(unsigned long)' which is likely to
> >> be 4 or 8.
> >
> > If the size can be 4 or 8, then using 64 universally is not correct.
> > Why not use sizeof() * 8 (or << 3)?
>
> Better yet, why not put this patch in the kernel first:
>
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index d96a6118d26a..a8838c87668e 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -52,6 +52,8 @@
>
>  #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]) +
> __must_be_array(arr))
>
> +#define bitsizeof(x)   (sizeof((x)) << 3)
> +
>  #define u64_to_user_ptr(x) (           \
>  {                                      \
>         typecheck(u64, x);              \
>
> then start going around replacing all these hard coded numbers with the
> use of bitsizeof().  It can be applied not just to the find_first*bit()
> routines, but to a bunch of other routines too.  Just look at
> include/linux/bitmap.h and any that have nbits as an argument are
> candidates.

There is BITS_PER_LONG define for that. There is actual use of it in mlx5 for
the similar code pieces.

>
>
> --
> Doug Ledford <dledford@redhat.com>
>     GPG Key ID: 0E572FDD
>




[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 819 bytes --]