On 8/26/2016 3:29 PM, Leon Romanovsky wrote:
> 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.
BITS_PER_LONG only works if your bitfield is a single long. It doesn't
work for other bitfields. What I posted above will work for anything.
--
Doug Ledford <dledford@xxxxxxxxxx>
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