"Serge E. Hallyn" <se...@hallyn.com> writes:

> This is so that userspace can distinguish a mount made in a cgroup
> namespace from a bind mount from a cgroup subdirectory.

To do that do you need to print the path, or is an extra option that
reveals nothing except that it was a cgroup mount sufficient?

Is there any practical difference between a mount in a namespace and a
bind mount?

Given the way the conversation has been going I think it would be good
to see the answers to these questions.  Perhaps I missed it but I
haven't seen the answers to those questions.

Eric


>
> Signed-off-by: Serge Hallyn <serge.hal...@ubuntu.com>
> ---
> Changelog: 2016-04-13: pass kernfs_node rather than dentry to show_options
> ---
>  fs/kernfs/mount.c      |  2 +-
>  include/linux/kernfs.h |  3 ++-
>  kernel/cgroup.c        | 28 +++++++++++++++++++++++++++-
>  3 files changed, 30 insertions(+), 3 deletions(-)
>
> diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
> index f73541f..58e8a86 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->d_fsdata, root);
>       return 0;
>  }
>  
> diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
> index c06c442..72b4081 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 kernfs_node *kn,
> +                         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..4d26d07 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -1593,7 +1593,31 @@ 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 kernfs_node 
> *knode,
> +                            struct kernfs_root *kroot)
> +{
> +     char *nsroot;
> +     int len, ret;
> +
> +     if (!kroot)
> +             return;
> +     len = kernfs_path_from_node(knode, kroot->kn, NULL, 0);
> +     if (len <= 0)
> +             return;
> +     nsroot = kzalloc(len + 1, GFP_ATOMIC);
> +     if (!nsroot)
> +             return;
> +     ret = kernfs_path_from_node(knode, kroot->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 kernfs_node *kn,
>                              struct kernfs_root *kf_root)
>  {
>       struct cgroup_root *root = cgroup_root_from_kf(kf_root);
> @@ -1619,6 +1643,8 @@ 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, kn, kf_root);
> +
>       return 0;
>  }

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