pid namespaces: helpers to obtain pid numbers

When showing pid to user or getting the pid numerical id for in-kernel use the
value of this id may differ depending on the namespace.

This set of helpers is used to get the global pid nr, the virtual (i.e.  seen
by task in its namespace) nr and the nr as it is seen from the specified
namespace.

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, 13 insertions, 0 deletions

diff --git a/kernel/pid.c b/kernel/pid.c
index 8132a6ddfa10..6eb14841b734 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -376,6 +376,19 @@ struct pid *find_get_pid(pid_t nr)
         return pid;
 }
 
+pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns)
+{
+        struct upid *upid;
+        pid_t nr = 0;
+
+        if (pid && ns->level <= pid->level) {
+                upid = &pid->numbers[ns->level];
+                if (upid->ns == ns)
+                        nr = upid->nr;
+        }
+        return nr;
+}
+
 /*
  * Used by proc to find the first pid that is greater then or equal to nr.
  *