From mboxrd@z Thu Jan 1 00:00:00 1970 From: Madper Xie Subject: Re: [PATCH] Make efi-pstore return a unique id Date: Sat, 02 Nov 2013 09:15:35 +0800 Message-ID: <87mwln7geg.fsf@redhat.com> References: <87ppqk6qvx.fsf@redhat.com> <52740A3A.70202@nod.at> Mime-Version: 1.0 Content-Type: text/plain Return-path: In-reply-to: <52740A3A.70202@nod.at> Sender: linux-kernel-owner@vger.kernel.org To: Richard Weinberger Cc: Seiji Aguchi , Tony Luck , Madper Xie , "matt.fleming@intel.com" , linux-kernel , Linux EFI , =?utf-8?B?6LCi5oiQ6aqP?= List-Id: linux-efi@vger.kernel.org richard@nod.at writes: > Am 01.11.2013 20:22, schrieb Seiji Aguchi: >>>>> +{ >>>>> + char id_str[64]; >>>>> + u64 id = 0; >>>>> + >>>>> + sprintf(id_str, "%lu%u%d", timestamp, part, count); >>>>> + if (kstrtoull(id_str, 10, &id)) >>>>> + pr_warn("efi-pstore: failed to generate id\n"); >>>>> + return id; >>>>> +} >>>> >>>> This is just odd. You make a string from three ints and then a parse >>>> it to a int again. >>> >>> Agreed. I liked your ((timestamp * 100 + part) * 100 + count function much >>> more than this. >> >> I was worried that the part and count could be more than 100. >> If it happens, the id may not be unique... >> >> But, currently, size of nvram storage is limited, so it is a corner case. >> I respect your opinion. > Is it really safe? for now I have more than 100 entries: [root@dhcp-13-41 rhel6]# ls -l /dev/pstore/ | wc -l 124 The maximum part of my records is 16. But I not sure if overflow will happen in some special case, like a very long dmesg output. or a server never reboot, and too many warnings make count++... So is it necessary to check count < 100 or 100 =< count < 1000 ? > What about feeding the bytes of all three integers into a non-cryptographic hash function? > Using this way you get a cheap unique id. > > Thanks, > //richard > -- > 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/ -- Best, Madper Xie.