linux-kernel - Re: [PATCH 1/2] pid: Implement ns_of

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Message-ID: <20081213023454.GA4147@us.ibm.com>
Date:	Fri, 12 Dec 2008 18:34:54 -0800
From:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
To:	Andrew Morton <akpm@...l.org>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Oleg Nesterov <oleg@...sign.ru>, roland@...hat.com,
	bastian@...di.eu.org, Pavel Emelyanov <xemul@...nvz.org>,
	sukadev@...ux.vnet.ibm.com, Containers <containers@...ts.osdl.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] pid: Implement ns_of_pid

Resending with complete cc list.

Sukadev Bhattiprolu [sukadev@...ux.vnet.ibm.com] wrote:
| This and following patch were discussed a couple of times but I
| did not see any objections to them. The ns_of_pid() introduced
| here will also be used in a follow-on patch to fix si_pid from
| mqueue.
| 
| ---
| From: Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
| Date: Fri, 12 Dec 2008 11:44:55 -0800
| Subject: [PATCH 1/2] 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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