Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965559AbcLVSYU (ORCPT ); Thu, 22 Dec 2016 13:24:20 -0500 Received: from out02.mta.xmission.com ([166.70.13.232]:45269 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932261AbcLVSYT (ORCPT ); Thu, 22 Dec 2016 13:24:19 -0500 From: ebiederm@xmission.com (Eric W. Biederman) To: Peter Zijlstra Cc: Hari Bathini , ast@fb.com, lkml , acme@kernel.org, alexander.shishkin@linux.intel.com, mingo@redhat.com, daniel@iogearbox.net, rostedt@goodmis.org, Ananth N Mavinakayanahalli , sargun@sargun.me, Aravinda Prasad , brendan.d.gregg@gmail.com References: <20161216075703.GE3124@twins.programming.kicks-ass.net> <2c0e3bbb-90a1-b5a4-b6d4-19c419ef5411@linux.vnet.ibm.com> <20161216200536.GI3124@twins.programming.kicks-ass.net> <1702a267-0ce6-86da-7755-11a375e450e2@linux.vnet.ibm.com> <20161221132452.GT3124@twins.programming.kicks-ass.net> <2af6cd8b-46f3-b60d-581f-30269ea65d53@linux.vnet.ibm.com> <87d1gkig3w.fsf@xmission.com> <20161222075327.GV3124@twins.programming.kicks-ass.net> <87r350gtay.fsf@xmission.com> <20161222132449.GL3107@twins.programming.kicks-ass.net> Date: Fri, 23 Dec 2016 07:20:56 +1300 In-Reply-To: <20161222132449.GL3107@twins.programming.kicks-ass.net> (Peter Zijlstra's message of "Thu, 22 Dec 2016 14:24:49 +0100") Message-ID: <87lgv7akqf.fsf@xmission.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1cK82E-00086R-Qi;;;mid=<87lgv7akqf.fsf@xmission.com>;;;hst=in02.mta.xmission.com;;;ip=101.100.131.98;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX18GeiDhdCArWM/OIkBCAGN3I4VsQ16pd3k= X-SA-Exim-Connect-IP: 101.100.131.98 X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-Report: * -1.0 ALL_TRUSTED Passed through trusted hosts only via SMTP * 0.7 XMSubLong Long Subject * 0.0 T_TM2_M_HEADER_IN_MSG BODY: No description available. * 0.8 BAYES_50 BODY: Bayes spam probability is 40 to 60% * [score: 0.4392] * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa07 1397; Body=1 Fuz1=1 Fuz2=1] * 0.0 T_TooManySym_01 4+ unique symbols in subject X-Spam-DCC: XMission; sa07 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: ;Peter Zijlstra X-Spam-Relay-Country: X-Spam-Timing: total 5546 ms - load_scoreonly_sql: 0.03 (0.0%), signal_user_changed: 3.4 (0.1%), b_tie_ro: 2.4 (0.0%), parse: 1.28 (0.0%), extract_message_metadata: 17 (0.3%), get_uri_detail_list: 1.64 (0.0%), tests_pri_-1000: 7 (0.1%), tests_pri_-950: 1.39 (0.0%), tests_pri_-900: 1.00 (0.0%), tests_pri_-400: 22 (0.4%), check_bayes: 21 (0.4%), b_tokenize: 6 (0.1%), b_tok_get_all: 6 (0.1%), b_comp_prob: 3.0 (0.1%), b_tok_touch_all: 2.8 (0.1%), b_finish: 0.67 (0.0%), tests_pri_0: 168 (3.0%), check_dkim_signature: 0.75 (0.0%), check_dkim_adsp: 4.1 (0.1%), tests_pri_500: 5321 (95.9%), poll_dns_idle: 5314 (95.8%), rewrite_mail: 0.00 (0.0%) Subject: Re: [PATCH v4 1/3] perf: add PERF_RECORD_NAMESPACES to include namespaces related info X-Spam-Flag: No X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1306 Lines: 37 Peter Zijlstra writes: > On Thu, Dec 22, 2016 at 11:19:17PM +1300, Eric W. Biederman wrote: >> Peter Zijlstra writes: >> >> > On Thu, Dec 22, 2016 at 08:21:23PM +1300, Eric W. Biederman wrote: >> >> >> >> And please make the array the last item in the structure so that >> >> expanding or contracting it does not affect the ability to read the rest >> >> of the structure. >> > >> > Sorry, sample_id must be last, because hysterical crud :/ >> > >> > (basically because that was the only way to add a field to records like >> > PERF_RECORD_MMAP which used the record length to determine the >> > filename[] length, yes I know, we won't ever do that again). >> >> Why does historical crud need to affect new records? > > Because now the userspace parser expects sample_id to be the tail > field. Basically decoding a record now looks like: > > if (sample_id_all) { > sample_id = (sample_id *)((char *)record + record->size - sizeof(sample_id)); > record->size -= sizeof(sample_id); > } > /* process record */ > > We could of course create more exceptions.. > >> Totally confused. This looks like a major mess. > > Not major, but yes, its ugly, but its also ABI :-( Fair enough. I will just avert my eyes now and deal with my own challenges. Eric