Subject: Re: [PATCH v2] net: bluetooth: hci_sock: Use 'const void *' instead of 'void *' for 2nd parameter of hci_test_bit()

From: Chen Gang S <[email-masked]>
Date: Thu, 05 Feb 2015 05:47:37 +0800

On 2/5/15 05:09, Marcel Holtmann wrote:
> Hi Sergei,
> 
>>>> -static inline int hci_test_bit(int nr, void *addr)
>>>> +static inline int hci_test_bit(int nr, const void *addr)
>>>>  {
>>>>  	return *((__u32 *) addr + (nr >> 5)) & ((__u32) 1 << (nr & 31));
>>>>  }
>>
>>> Is there a 'standard' function lurking that will do the above.
>>> On x86 the cpus 'bit test' instruction will handle bit numbers
>>> greater than the word size - so it can be a single instruction.
>>
>>   Of course, there's test_bit().
> 
> we did leave hci_test_bit in the code since there are some userspace facing API that we can not change. Remember that the origin of this code is from 2.4.6 kernel.
> 
> So we can only change this if you can ensure not to break the userspace API. So might want to write unit tests to ensure working HCI filter before even considering touching this.
> 

For me, we have to remain hci_test_bit(), it is for "__u32 *" (which we
can not change). The common test_bit() is for "unsigned long *", in this
case, I guess it may cause issue under 64-bit environments.

Thanks.
-- 
Chen Gang

Open, share, and attitude like air, water, and life which God blessed