[PATCH 7/7] pid: get pid_t ppid of task in init_pid_ns

[Richard Guy Briggs]

Added the functions task_ppid_nr_ns() and task_ppid_nr() to abstract the lookup
of the PPID (real_parent's pid_t) of a process, including rcu locking, in the
arbitrary and init_pid_ns.
This provides an alternative to sys_getppid(), which is relative to the child
process' pid namespace.

(informed by ebiederman's 6c621b7e)
Cc: stable at vger.kernel.org
Cc: Eric W. Biederman <ebiederm at xmission.com>
Signed-off-by: Richard Guy Briggs <rgb at redhat.com>
---
 include/linux/sched.h |   18 ++++++++++++++++++
 1 files changed, 18 insertions(+), 0 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 2016d92..cba2486 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1561,6 +1561,24 @@ static inline pid_t task_tgid_vnr(const struct task_struct *tsk)
 }
 
 
+static int pid_alive(const struct task_struct *p);
+static inline pid_t task_ppid_nr_ns(const struct task_struct *tsk, struct pid_namespace *ns)
+{
+	pid_t pid = 0;
+
+	rcu_read_lock();
+	if (pid_alive(tsk))
+		pid = task_tgid_nr_ns(rcu_dereference(tsk->real_parent), ns);
+	rcu_read_unlock();
+
+	return pid;
+}
+
+static inline pid_t task_ppid_nr(const struct task_struct *tsk)
+{
+	return task_ppid_nr_ns(tsk, &init_pid_ns);
+}
+
 static inline pid_t task_pgrp_nr_ns(const struct task_struct *tsk,
 					struct pid_namespace *ns)
 {
-- 
1.7.1