From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756871AbaE2Jlw (ORCPT ); Thu, 29 May 2014 05:41:52 -0400 Received: from relay.parallels.com ([195.214.232.42]:46383 "EHLO relay.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756119AbaE2Jlu (ORCPT ); Thu, 29 May 2014 05:41:50 -0400 Message-ID: <538700B5.5070601@parallels.com> Date: Thu, 29 May 2014 13:41:09 +0400 From: Pavel Emelyanov User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:13.0) Gecko/20120605 Thunderbird/13.0 MIME-Version: 1.0 To: Richard Weinberger CC: Vasily Kulikov , , Serge Hallyn , , Oleg Nesterov , David Howells , "Eric W. Biederman" , Andrew Morton , Al Viro Subject: Re: [PATCH v2] /proc/pid/status: show all sets of pid according to ns References: <1401272683-1659-1-git-send-email-chenhanxiao@cn.fujitsu.com> <5385DA19.2060008@parallels.com> <20140528182824.GA5057@cachalot> <53863889.9080509@parallels.com> <20140529055954.GA10354@cachalot> <5386F8EA.8050501@parallels.com> <5386FC0C.9000307@nod.at> In-Reply-To: <5386FC0C.9000307@nod.at> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.24.36.87] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/29/2014 01:21 PM, Richard Weinberger wrote: > Am 29.05.2014 11:07, schrieb Pavel Emelyanov: >> On 05/29/2014 09:59 AM, Vasily Kulikov wrote: >>> On Wed, May 28, 2014 at 23:27 +0400, Pavel Emelyanov wrote: >>>> On 05/28/2014 10:28 PM, Vasily Kulikov wrote: >>>>> On Wed, May 28, 2014 at 16:44 +0400, Pavel Emelyanov wrote: >>>>> It will be simplier >>>>> to parse the file -- if 'ns_ids' file contains some ID then this ID for >>>>> every ns can be obtained regardless of the specific ID name (SID, PID, >>>>> PGID, etc.). >>>> >>>> True, but given a task PID how to determine which pid namespaces it lives in >>>> to get the idea of how PIDs map to each other? Maybe we need some explicit >>>> API for converting (ID, NS1, NS2) into (ID)? >>> >>> AFAIU the idea of the patch is to add a new debugging information which >>> can be trivially obtained via 'cat /proc/...': >> >> I agree, but this ability will be very useful by checkpoint-restore project >> too and I'd really appreciate if the API we have for that would be scalable >> enough. Per-task proc file works for me, but how about sid-s and pgid-s? > > What kind of information does CRIU need? We need to know what pid namespaces a task lives in and how pid, sid and pgid look in all of them. A short example with pids only Task t1 with pid 2, lives in init pid ns calls clone(CLONE_NEWPID), creates ns1 with task t2 having pid (3, 1), then t2 calls clone(CLONE_NEWPID) again and creates ns2 with task t3 having pid (4, 5, 1). I.e. the trees look like this: init_pid_ns ns1 ns2 t1 2 t2 `- 3 1 t3 `- 4 `- 5 1 Also note, that /proc/pid/ns will show us that t1 lives in init_pid_ns, t2 lives in ns1 and t3 lives in ns2. Now if we come from init pid ns with criu and try to dump task with pid 3 (i.e. the t2), the existing kernel API can tell us that: a) t2 lives in ns1 != init_pid_ns (via /proc/pid/ns link) b) t3 lives in ns2 != init_pid_ns c) t2 has pid 3 (via init's /proc) in init ns and pid 1 in its ns (via t2's /proc) d) t3 has pid 4 in init ns and pid 1 in its ns what we also need to know and don't yet have an API for is e) ns2 is the child of ns1 f) t3 has pid 5 in ns1 Thanks, Pavel