@@ -37,7 +37,7 @@ 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;
}
@@ -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);
@@ -1589,7 +1589,32 @@ static int rebind_subsystems(struct cgroup_root *dst_root,
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);
@@ -1615,6 +1640,8 @@ 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;
}
[ note - this is a version of the patch I just sent to lkml ported to our xenial tree. It's needed for things like docker and lxc to be certain of which cgroup tasks file is their own in certain nesting situations. We currently work around it by blindly assuming that there are no legacy container managers running on cgroup-ns-enabled kernels ] 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 <serge.hallyn@ubuntu.com> --- fs/kernfs/mount.c | 2 +- include/linux/kernfs.h | 3 ++- kernel/cgroup.c | 29 ++++++++++++++++++++++++++++- 4 files changed, 37 insertions(+), 5 deletions(-)