From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-db5eur01on0113.outbound.protection.outlook.com ([104.47.2.113]:61807 "EHLO EUR01-DB5-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1757179AbcGZVBl (ORCPT ); Tue, 26 Jul 2016 17:01:41 -0400 Date: Tue, 26 Jul 2016 11:25:24 -0700 From: Andrew Vagin To: "Michael Kerrisk (man-pages)" CC: "Eric W. Biederman" , Andrey Vagin , Serge Hallyn , "criu@openvz.org" , Linux API , Linux Containers , LKML , James Bottomley , linux-fsdevel , Alexander Viro Subject: Re: [PATCH 0/5 RFC] Add an interface to discover relationships between namespaces Message-ID: <20160726182524.GA328@outlook.office365.com> References: <20160721210650.GA10989@outlook.office365.com> <1515f5f2-5a49-fcab-61f4-8b627d3ba3e2@gmail.com> <87lh0pg8jx.fsf@x220.int.ebiederm.org> <44ca0e41-dc92-45b1-2a6c-c41a048a072d@gmail.com> <87r3ahepb4.fsf@x220.int.ebiederm.org> <20160726025455.GC26206@outlook.office365.com> <3390535b-0660-757f-aeba-c03d936b3485@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset="koi8-r" Content-Disposition: inline In-Reply-To: <3390535b-0660-757f-aeba-c03d936b3485@gmail.com> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Tue, Jul 26, 2016 at 10:03:25AM +0200, Michael Kerrisk (man-pages) wrote: > On 07/26/2016 04:54 AM, Andrew Vagin wrote: > > On Mon, Jul 25, 2016 at 09:59:43AM -0500, Eric W. Biederman wrote: > > > "Michael Kerrisk (man-pages)" writes: > > > > [snip] > > > > > [snip] > > > > > > So, from my point of view, the important piece that was missing from > > > > > > your commit message was the note to use readlink("/proc/self/fd/%d") > > > > > > on the returned FDs. I think that detail needs to be part of the > > > > > > commit message (and also the man page text). I think it even be > > > > > > helpful to include the above program as part of the commit message: > > > > > > it helps people more quickly grasp the API. > > > > > > > > > > Please, please make the standard way to compare these things fstat. > > > > > That is much less magic than a symlink, and a little more future proof. > > > > > Possibly even kcmp. > > > > I like the idea to use kcmp to compare namespaces. I am going to add this > > functionality to kcmp and describe all these in the man page. > > Hi Andrey, > > Can you briefly sketch out the proposed API and how it would be used? > I'd find it useful to see that even before the implementation. Sure. If a process wants to compare two namespaces, it needs to get file descriptors for them (open /proc/PID/ns/XXX, use new ioctl-s, find a process which has them), and then it calls kcmp(pid1, pid2, KCMP_NSFD, ns_fd1, ns_fd2) For example, if we want to compare pid namespaces for 1 and 2 processes: pid = getpid(); ns_fd1 = open("/proc/1/ns/pid") ns_fd2 = open("/proc/2/ns/pid") if (!kcmp(pid, pid, KCMP_NSFD, ns_fd1, ns_fd2)) printf("Both processes live in the same pid namespace\n"); Thanks, Andrew > > Cheers, > > Michael > > > -- > Michael Kerrisk > Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ > Linux/UNIX System Programming Training: http://man7.org/training/