Return-Path: Message-ID: <54D29379.8050104@sunrus.com.cn> Date: Thu, 05 Feb 2015 05:47:37 +0800 From: Chen Gang S MIME-Version: 1.0 To: Marcel Holtmann , Sergei Shtylyov CC: David Laight , "Gustavo F. Padovan" , Johan Hedberg , "David S. Miller" , "linux-bluetooth@vger.kernel.org" , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v2] net: bluetooth: hci_sock: Use 'const void *' instead of 'void *' for 2nd parameter of hci_test_bit() References: <54CFE8BE.5030700@sunrus.com.cn> <063D6719AE5E284EB5DD2968C1650D6D1CADA5E1@AcuExch.aculab.com> <54D27D68.7040501@cogentembedded.com> <0AB99BEA-C379-439C-AD80-5F2122AE37E5@holtmann.org> In-Reply-To: <0AB99BEA-C379-439C-AD80-5F2122AE37E5@holtmann.org> Content-Type: text/plain; charset=windows-1252 Sender: linux-kernel-owner@vger.kernel.org List-ID: 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