Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757157AbbBEKPn (ORCPT ); Thu, 5 Feb 2015 05:15:43 -0500 Received: from smtp-out4.electric.net ([192.162.216.181]:63666 "EHLO smtp-out4.electric.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752911AbbBEKPl convert rfc822-to-8bit (ORCPT ); Thu, 5 Feb 2015 05:15:41 -0500 From: David Laight To: "'Chen Gang S'" , Marcel Holtmann , Sergei Shtylyov CC: "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() Thread-Topic: [PATCH v2] net: bluetooth: hci_sock: Use 'const void *' instead of 'void *' for 2nd parameter of hci_test_bit() Thread-Index: AQHQPywzeR6i5TQh3kGdfi5IMQnXPJzgZU2AgACKbgCAAA+8gIAACpKAgADPPzA= Date: Thu, 5 Feb 2015 10:14:51 +0000 Message-ID: <063D6719AE5E284EB5DD2968C1650D6D1CADC42B@AcuExch.aculab.com> References: <54CFE8BE.5030700@sunrus.com.cn> <063D6719AE5E284EB5DD2968C1650D6D1CADA5E1@AcuExch.aculab.com> <54D27D68.7040501@cogentembedded.com> <0AB99BEA-C379-439C-AD80-5F2122AE37E5@holtmann.org> <54D29379.8050104@sunrus.com.cn> In-Reply-To: <54D29379.8050104@sunrus.com.cn> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.202.99.200] Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 X-Outbound-IP: 213.249.233.130 X-Env-From: David.Laight@ACULAB.COM X-PolicySMART: 3396946, 3397078 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1690 Lines: 44 From: Chen Gang S [mailto:gang.chen@sunrus.com.cn] > 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. Except that half the time you are passing a 'long *' and you haven't explained why this isn't broken on 64bit architectures. Note that on LE systems the size of the accesses used to access a dense bit array don't matter. This is not true of BE systems. David -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/