On 2/5/15 18:14, David Laight wrote: > From: Chen Gang S [mailto:gang.chen@xxxxxxxxxxxxx] >> 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. > Maybe we are misunderstanding with each other (excuse me for my pool English). What I want to say is: - hci_test_bit() is OK (current implementation can not cause issue for 64-bit machine). - But if we use test_bit(), I guess it will cause issue for 64-bit machine. > 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. > Yes, what you said above sounds reasonable to me, too. Thanks. -- Chen Gang Open, share, and attitude like air, water, and life which God blessed -- To unsubscribe from this list: send the line "unsubscribe linux-bluetooth" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
