Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757992AbcCUXli (ORCPT ); Mon, 21 Mar 2016 19:41:38 -0400 Received: from h2.hallyn.com ([78.46.35.8]:48782 "EHLO h2.hallyn.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750920AbcCUXlg (ORCPT ); Mon, 21 Mar 2016 19:41:36 -0400 Date: Mon, 21 Mar 2016 18:41:33 -0500 From: "Serge E. Hallyn" To: tj@kernel.org, linux-api@vger.kernel.org, adityakali@google.com, Linux Containers , "Eric W. Biederman" , cgroups@vger.kernel.org, lkml Subject: [RFC PATCH] cgroup namespaces: add a 'nsroot=' mountinfo field Message-ID: <20160321234133.GA22463@mail.hallyn.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3249 Lines: 101 One practical problem I've found with cgroup namespaces is that there is no way to disambiguate between a cgroupfs mount which was done in a cgroup namespace, and a bind mount of a cgroupfs directory. So whether I do unshare --cgroup -- bash -c "mount -t cgroup -o freezer f /mnt; cat /proc/self/mountinfo" or whether I just mount --bind /sys/fs/cgroup/freezer/$(awk -F: '/freezer/ { print $3 }' /proc/self/cgroup) /mnt 'mount root' field (field 3) in /proc/self/mountinfo will show the same thing, the result of awk -F: '/freezer/ { print $3 }' /proc/self/cgroup. This patch adds a 'nsroot=' field to cgroup mountinfo entries, so that userspace can distinguish a mount made in a cgroup namespace from a bind mount from a cgroup subdirectory. Signed-off-by: Serge Hallyn --- fs/kernfs/mount.c | 2 +- include/linux/kernfs.h | 3 ++- kernel/cgroup.c | 29 ++++++++++++++++++++++++++++- 3 files changed, 31 insertions(+), 3 deletions(-) diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c index b67dbcc..58f59fd 100644 --- a/fs/kernfs/mount.c +++ b/fs/kernfs/mount.c @@ -36,7 +36,7 @@ static int kernfs_sop_show_options(struct seq_file *sf, struct dentry *dentry) struct kernfs_syscall_ops *scops = root->syscall_ops; if (scops && scops->show_options) - return scops->show_options(sf, root); + return scops->show_options(sf, dentry, root); return 0; } diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h index c06c442..3124b91 100644 --- a/include/linux/kernfs.h +++ b/include/linux/kernfs.h @@ -145,7 +145,8 @@ struct kernfs_node { */ struct kernfs_syscall_ops { int (*remount_fs)(struct kernfs_root *root, int *flags, char *data); - int (*show_options)(struct seq_file *sf, struct kernfs_root *root); + int (*show_options)(struct seq_file *sf, struct dentry *dentry, + struct kernfs_root *root); int (*mkdir)(struct kernfs_node *parent, const char *name, umode_t mode); diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 671dc05..806d1e7 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -1593,7 +1593,32 @@ static int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask) return 0; } -static int cgroup_show_options(struct seq_file *seq, +static void cgroup_show_nsroot(struct seq_file *seq, struct dentry *dentry, + struct kernfs_root *kf_root) +{ + struct kernfs_node *d_kn = dentry->d_fsdata; + char *nsroot; + int len, ret; + + if (!kf_root) + return; + len = kernfs_path_from_node(d_kn, kf_root->kn, NULL, 0); + if (len <= 0) + return; + nsroot = kzalloc(len + 1, GFP_ATOMIC); + if (!nsroot) + return; + ret = kernfs_path_from_node(d_kn, kf_root->kn, nsroot, len + 1); + if (ret <= 0 || ret > len) + goto out; + + seq_show_option(seq, "nsroot", nsroot); + +out: + kfree(nsroot); +} + +static int cgroup_show_options(struct seq_file *seq, struct dentry *dentry, struct kernfs_root *kf_root) { struct cgroup_root *root = cgroup_root_from_kf(kf_root); @@ -1619,6 +1644,8 @@ static int cgroup_show_options(struct seq_file *seq, seq_puts(seq, ",clone_children"); if (strlen(root->name)) seq_show_option(seq, "name", root->name); + cgroup_show_nsroot(seq, dentry, kf_root); + return 0; } -- 2.7.3