From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752800AbbIPHhn (ORCPT ); Wed, 16 Sep 2015 03:37:43 -0400 Received: from forward-corp1m.cmail.yandex.net ([5.255.216.100]:48668 "EHLO forward-corp1m.cmail.yandex.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751904AbbIPHhk (ORCPT ); Wed, 16 Sep 2015 03:37:40 -0400 Authentication-Results: smtpcorp4.mail.yandex.net; dkim=pass header.i=@yandex-team.ru Subject: Re: [PATCH RFC] pidns: introduce syscall getvpid To: Serge Hallyn , =?UTF-8?Q?St=c3=a9phane_Graber?= References: <20150915120924.14818.49490.stgit@buzz> <87h9mvg3kw.fsf@x220.int.ebiederm.org> <55F832D2.1070605@yandex-team.ru> <20150915151729.GA144242@dakara> <20150915174143.GE4699@ubuntumail> Cc: linux-api@vger.kernel.org, containers@lists.linux-foundation.org, Oleg Nesterov , linux-kernel@vger.kernel.org, "Eric W. Biederman" , Andrew Morton , Linus Torvalds From: Konstantin Khlebnikov Message-ID: <55F91C3D.1040209@yandex-team.ru> Date: Wed, 16 Sep 2015 10:37:33 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.2.0 MIME-Version: 1.0 In-Reply-To: <20150915174143.GE4699@ubuntumail> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 15.09.2015 20:41, Serge Hallyn wrote: > Quoting Stéphane Graber (stgraber@ubuntu.com): >> On Tue, Sep 15, 2015 at 06:01:38PM +0300, Konstantin Khlebnikov wrote: >>> On 15.09.2015 17:27, Eric W. Biederman wrote: >>>> Konstantin Khlebnikov writes: >>>> >>>>> pid_t getvpid(pid_t pid, pid_t source, pid_t target); >>>>> >>>>> This syscall converts pid from one pid-ns into pid in another pid-ns: >>>>> it takes @pid in namespace of @source task (zero for current) and >>>>> returns related pid in namespace of @target task (zero for current too). >>>>> If pid is unreachable from target pid-ns then it returns zero. >>>> >>>> This interface as presented is inherently racy. It would be better >>>> if source and target were file descriptors referring to the namespaces >>>> you wish to translate between. >>> >>> Yep, it's racy. As well as any operation with non-child pids. >>> With file descriptors for source/target result will be racy anyway. >>> >>>> >>>>> Such conversion is required for interaction between processes from >>>>> different pid-namespaces. For example when system service talks with >>>>> client from isolated container via socket about task in container: >>>> >>>> Sockets are already supported. At least the metadata of sockets is. >>>> >>>> Maybe we need this but I am not convinced of it's utility. >>>> >>>> What are you trying to do that motivates this? >>> >>> I'm working on hierarchical container management system which >>> allows to create and control nested sub-containers from containers >>> ( https://github.com/yandex/porto ). Main server works in host and >>> have to interact with all levels of nested namespaces. This syscall >>> makes some operations much easier: server must remember only pid in >>> host pid namespace and convert it into right vpid on demand. >> >> Note that as Eric said earlier, sending a PID inside a ucred through a >> unix socket will have the pid translated. >> >> So while your solution certainly should be faster, you can already achieve >> what you want today by doing: >> >> == Translate PID in container to PID in host >> - open a socket >> - setns to container's pidns >> - send ucred from that container containing the requested container PID >> - host sees the host PID >> >> == Translate PID on host to PID in container >> - open a socket >> - setns to container's pidns >> - send ucred from the host containing the request host PID >> (send will fail if the host PID isn't part of that container) >> - container sees the container PID > > In addition, since commit e4bc332451 : /proc/PID/status: show all sets of pid according to ns > we now also have 'NSpid' etc in /proc/$$/status. > As I see this works perfectly only for converting host pid into virtual. Backward conversion is troublesome: we have to scan all pids in host procfs and somehow filter tasks from container and its sub-pid-ns. Or I am missing something trivial? -- Konstantin