pid namespaces: make proc have multiple superblocks - one for each namespace

Each pid namespace have to be visible through its own proc mount.  Thus we
need to have per-namespace proc trees with their own superblocks.

We cannot easily show different pid namespace via one global proc tree, since
each pid refers to different tasks in different namespaces.  E.g.  pid 1
refers to the init task in the initial namespace and to some other task when
seeing from another namespace.  Moreover - pid, exisintg in one namespace may
not exist in the other.

This approach has one move advantage is that the tasks from the init namespace
can see what tasks live in another namespace by reading entries from another
proc tree.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Cc: Paul Menage <menage@google.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
index 14376ebf4ba..416d4e4ce94 100644
--- a/include/linux/pid_namespace.h
+++ b/include/linux/pid_namespace.h
@@ -23,6 +23,9 @@ struct pid_namespace {
         struct kmem_cache *pid_cachep;
         int level;
         struct pid_namespace *parent;
+#ifdef CONFIG_PROC_FS
+        struct vfsmount *proc_mnt;
+#endif
 };
 
 extern struct pid_namespace init_pid_ns;