linux-kernel - [RFC][PATCH 1/5] pid: Implement ns_of

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Date:	Tue, 25 Nov 2008 19:44:42 -0800
From:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
To:	oleg@...hat.com, ebiederm@...ssion.com, roland@...hat.com
Cc:	daniel@...ac.com, xemul@...nvz.org, containers@...ts.osdl.org,
	linux-kernel@...r.kernel.org, sukadev@...ibm.com
Subject: [RFC][PATCH 1/5] pid: Implement ns_of_pid

>From f3dd53544a8a7a1c43009f686cbadec561e5a489 Mon Sep 17 00:00:00 2001
From: Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
Date: Mon, 10 Nov 2008 19:03:56 -0800
Subject: [PATCH 1/5] pid: Implement ns_of_pid

A current problem with the pid namespace is that it is
easy to do pid related work after exit_task_namespaces which
drops the nsproxy pointer.

However if we are doing pid namespace related work we are
always operating on some struct pid which retains the pid_namespace
pointer of the pid namespace it was allocated in.

So provide ns_of_pid which allows us to find the pid
namespace a pid was allocated in.

Using this we have the needed infrastructure to do pid
namespace related work at anytime we have a struct pid,
removing the chance of accidentally having a NULL
pointer dereference when accessing current->nsproxy.

Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>
---
 include/linux/pid.h |   11 +++++++++++
 1 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/include/linux/pid.h b/include/linux/pid.h
index d7e98ff..e9aec85 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -122,6 +122,17 @@ int next_pidmap(struct pid_namespace *pid_ns, int last);
 extern struct pid *alloc_pid(struct pid_namespace *ns);
 extern void free_pid(struct pid *pid);
 
+/* ns_of_pid returns the pid namespace in which the specified
+ * pid was allocated.
+ */
+static inline struct pid_namespace *ns_of_pid(struct pid *pid)
+{
+	struct pid_namespace *ns = NULL;
+	if (pid)
+		ns = pid->numbers[pid->level].ns;
+	return ns;
+}
+
 /*
  * the helpers to get the pid's id seen from different namespaces
  *
-- 
1.5.2.5

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