From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751701AbcETVYl (ORCPT ); Fri, 20 May 2016 17:24:41 -0400 Received: from mail-yw0-f196.google.com ([209.85.161.196]:35792 "EHLO mail-yw0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751172AbcETVYj (ORCPT ); Fri, 20 May 2016 17:24:39 -0400 Cc: mtk.manpages@gmail.com, lkml , "Serge E. Hallyn" , Al Viro , Ram Pai To: Miklos Szeredi From: "Michael Kerrisk (man-pages)" Subject: Mount namespace "dominant peer group"? Message-ID: Date: Fri, 20 May 2016 16:24:18 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.0 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello Miklos, I'm working on some better documentation of mount namespaces, and there's a detail that puzzles me, and I hope you might be able to help, since you added the detail... In Documentation/filesystems/proc.txt there is this text in the description of /proc/PID/mountinfo: [[ Parsers should ignore all unrecognised optional fields. Currently the possible optional fields are: shared:X mount is shared in peer group X master:X mount is slave to peer group X propagate_from:X mount is slave and receives propagation from peer group X (*) unbindable mount is unbindable (*) X is the closest dominant peer group under the process's root. If X is the immediate master of the mount, or if there's no dominant peer group under the same root, then only the "master:X" field is present and not the "propagate_from:X" field. ]] What is a dominant peer group, as distinct from the immediate master? I can see in fs/proc_namespaces.c that there is this distinction made: [[ /* Tagged fields ("foo:X" or "bar") */ if (IS_MNT_SHARED(r)) seq_printf(m, " shared:%i", r->mnt_group_id); if (IS_MNT_SLAVE(r)) { int master = r->mnt_master->mnt_group_id; int dom = get_dominating_id(r, &p->root); seq_printf(m, " master:%i", master); if (dom && dom != master) seq_printf(m, " propagate_from:%i", dom); } ]] But I can't relate that to some user-space semantics. I suppose another way of asking my question is: how could I create a slave that is propagating from a peer group other than it's immediate master? Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/