[RFC][PATCH 01/16] Define/use task_active_pid_ns() wrapper

[sukadev at us.ibm.com]

Subject: Define/use task_active_pid_ns() wrapper

From: Sukadev Bhattiprolu <sukadev at us.ibm.com>


A process is visible in one or more pid namespaces, as it is known by
some pid_t in every ancestor pid namespace.  Every time the process
forks, the child process also gets a pid_t in every ancestor pid
namespace.

While a process is visible in >=1 pid namespaces, it can see pid_t's
in only one pid namespace.  We call this pid namespace it's "active
pid namespace", and it is always the youngest pid namespace in which
the process is known.

This patch defines/uses a wrapper to find the active pid namespace of a
process. The implementation of the wrapper will be changed in subsequent
patches when support for multiple pid namespaces are added.

Changelog:
	2.6.21-rc6-mm1:
	- Rename task_pid_ns() to task_active_pid_ns() to reflect that
	  a process can have multiple pid namespaces.

Signed-off-by: Sukadev Bhattiprolu <sukadev at us.ibm.com>
---
 fs/exec.c                     |    2 +-
 fs/proc/proc_misc.c           |    3 ++-
 include/linux/pid_namespace.h |    7 ++++++-
 kernel/exit.c                 |    5 +++--
 kernel/pid.c                  |    4 ++--
 5 files changed, 14 insertions(+), 7 deletions(-)

Index: lx26-21-mm2/include/linux/pid_namespace.h
===================================================================
--- lx26-21-mm2.orig/include/linux/pid_namespace.h	2007-05-22 16:59:29.000000000 -0700
+++ lx26-21-mm2/include/linux/pid_namespace.h	2007-05-22 17:49:52.000000000 -0700
@@ -37,9 +37,14 @@ static inline void put_pid_ns(struct pid
 	kref_put(&ns->kref, free_pid_ns);
 }
 
+static inline struct pid_namespace *task_active_pid_ns(struct task_struct *tsk)
+{
+	return tsk->nsproxy->pid_ns;
+}
+
 static inline struct task_struct *child_reaper(struct task_struct *tsk)
 {
-	return init_pid_ns.child_reaper;
+	return task_active_pid_ns(tsk)->child_reaper;
 }
 
 #endif /* _LINUX_PID_NS_H */
Index: lx26-21-mm2/fs/exec.c
===================================================================
--- lx26-21-mm2.orig/fs/exec.c	2007-05-22 16:59:29.000000000 -0700
+++ lx26-21-mm2/fs/exec.c	2007-05-22 17:49:52.000000000 -0700
@@ -629,7 +629,7 @@ static int de_thread(struct task_struct 
 	 * so it is safe to do it under read_lock.
 	 */
 	if (unlikely(tsk->group_leader == child_reaper(tsk)))
-		tsk->nsproxy->pid_ns->child_reaper = tsk;
+		task_active_pid_ns(tsk)->child_reaper = tsk;
 
 	zap_other_threads(tsk);
 	read_unlock(&tasklist_lock);
Index: lx26-21-mm2/fs/proc/proc_misc.c
===================================================================
--- lx26-21-mm2.orig/fs/proc/proc_misc.c	2007-05-22 16:59:29.000000000 -0700
+++ lx26-21-mm2/fs/proc/proc_misc.c	2007-05-22 16:59:34.000000000 -0700
@@ -94,7 +94,8 @@ static int loadavg_read_proc(char *page,
 		LOAD_INT(a), LOAD_FRAC(a),
 		LOAD_INT(b), LOAD_FRAC(b),
 		LOAD_INT(c), LOAD_FRAC(c),
-		nr_running(), nr_threads, current->nsproxy->pid_ns->last_pid);
+		nr_running(), nr_threads,
+		task_active_pid_ns(current)->last_pid);
 	return proc_calc_metrics(page, start, off, count, eof, len);
 }
 
Index: lx26-21-mm2/kernel/exit.c
===================================================================
--- lx26-21-mm2.orig/kernel/exit.c	2007-05-22 16:59:29.000000000 -0700
+++ lx26-21-mm2/kernel/exit.c	2007-05-22 17:49:52.000000000 -0700
@@ -876,8 +876,9 @@ fastcall NORET_TYPE void do_exit(long co
 	if (unlikely(!tsk->pid))
 		panic("Attempted to kill the idle task!");
 	if (unlikely(tsk == child_reaper(tsk))) {
-		if (tsk->nsproxy->pid_ns != &init_pid_ns)
-			tsk->nsproxy->pid_ns->child_reaper = init_pid_ns.child_reaper;
+		if (task_active_pid_ns(tsk) != &init_pid_ns)
+			task_active_pid_ns(tsk)->child_reaper =
+					init_pid_ns.child_reaper;
 		else
 			panic("Attempted to kill init!");
 	}
Index: lx26-21-mm2/kernel/pid.c
===================================================================
--- lx26-21-mm2.orig/kernel/pid.c	2007-05-22 16:59:29.000000000 -0700
+++ lx26-21-mm2/kernel/pid.c	2007-05-22 17:49:52.000000000 -0700
@@ -213,7 +213,7 @@ struct pid *alloc_pid(void)
 	if (!pid)
 		goto out;
 
-	nr = alloc_pidmap(current->nsproxy->pid_ns);
+	nr = alloc_pidmap(task_active_pid_ns(current));
 	if (nr < 0)
 		goto out_free;
 
@@ -358,7 +358,7 @@ struct pid *find_ge_pid(int nr)
 		pid = find_pid(nr);
 		if (pid)
 			break;
-		nr = next_pidmap(current->nsproxy->pid_ns, nr);
+		nr = next_pidmap(task_active_pid_ns(current), nr);
 	} while (nr > 0);
 
 	return pid;