Quoting Serge E. Hallyn (serge@xxxxxxxxxx):
> 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.
Hi Tejun,
no rush on the patch itself, I don't mind if i have to rewrite it from
scratch, but I'd like to get the patch into docker/libcontainer using it,
so can we decide on whether the syntax as shown here is ok?
thanks,
-serge
> Signed-off-by: Serge Hallyn <serge.hallyn@xxxxxxxxxx>
> ---
> 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
>
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