Subject: Use pid ns from pid->upid_list

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


We need to decouple pid namespace from nsproxy to allow getting and releasing
pid namespace independently from other namespaces. This is required since a
process's reference to its pid namespace must exist even after its references
to other namespaces are dropped during process exit.

With multiple pid namespaces, a process can have different pid_t values in
 different pid namespaces and 'struct upid' and the pid->upid_list list
provide this association of pid_t value with pid namespace for a process.

Use pid->upid_list list to find the active pid namespace of a process and
remove nsproxy->pid_namespace.

(Review note: My description of active pid namespace is probably long-winded.
              Appreciate any comments in explaining it better :-)

TODO:
	- Include pid_namespace in pid_hash() so processes with same pid_t
	  in different namespaces are on different hash lists.

Changelog:

	2.6.21-mm2-pidns3:
        - 'struct upid' used to be called 'struct pid_nr' and a list of these
           were hanging off of 'struct pid'. So, we renamed 'struct pid_nr'
           and now hold them in a statically sized array in 'struct pid' since
           the number of 'struct upid's for a process is known at process-
           creation time.

	[2.6.21-rc3-mm2]
	- Drop support for unshare() of pid namespace which simplifies cloning
	  of pid namespace and reorganize several functions.

Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
---
 include/linux/init_task.h     |    1 -
 include/linux/nsproxy.h       |    2 --
 include/linux/pid_namespace.h |    4 ++--
 kernel/nsproxy.c              |   10 ----------
 kernel/pid.c                  |   23 ++++++++++++++++-------
 5 files changed, 18 insertions(+), 22 deletions(-)

Index: lx26-21-mm2/include/linux/init_task.h
===================================================================
--- lx26-21-mm2.orig/include/linux/init_task.h	2007-05-22 16:59:49.000000000 -0700
+++ lx26-21-mm2/include/linux/init_task.h	2007-05-22 16:59:50.000000000 -0700
@@ -72,7 +72,6 @@
 
 extern struct nsproxy init_nsproxy;
 #define INIT_NSPROXY(nsproxy) {						\
-	.pid_ns		= &init_pid_ns,					\
 	.count		= ATOMIC_INIT(1),				\
 	.nslock		= __SPIN_LOCK_UNLOCKED(nsproxy.nslock),		\
 	.uts_ns		= &init_uts_ns,					\
Index: lx26-21-mm2/include/linux/nsproxy.h
===================================================================
--- lx26-21-mm2.orig/include/linux/nsproxy.h	2007-05-22 16:58:37.000000000 -0700
+++ lx26-21-mm2/include/linux/nsproxy.h	2007-05-22 16:59:50.000000000 -0700
@@ -7,7 +7,6 @@
 struct mnt_namespace;
 struct uts_namespace;
 struct ipc_namespace;
-struct pid_namespace;
 
 /*
  * A structure to contain pointers to all per-process
@@ -27,7 +26,6 @@ struct nsproxy {
 	struct uts_namespace *uts_ns;
 	struct ipc_namespace *ipc_ns;
 	struct mnt_namespace *mnt_ns;
-	struct pid_namespace *pid_ns;
 };
 extern struct nsproxy init_nsproxy;
 
Index: lx26-21-mm2/include/linux/pid_namespace.h
===================================================================
--- lx26-21-mm2.orig/include/linux/pid_namespace.h	2007-05-22 16:59:49.000000000 -0700
+++ lx26-21-mm2/include/linux/pid_namespace.h	2007-05-22 16:59:50.000000000 -0700
@@ -41,8 +41,8 @@ static inline void get_pid_ns(struct pid
 	kref_get(&ns->kref);
 }
 
-extern struct pid_namespace *copy_pid_ns(int flags, struct pid_namespace *ns);
 extern void free_pid_ns(struct kref *kref);
+extern struct pid_namespace *pid_active_pid_ns(struct pid *pid);
 
 static inline void put_pid_ns(struct pid_namespace *ns)
 {
@@ -51,7 +51,7 @@ static inline void put_pid_ns(struct pid
 
 static inline struct pid_namespace *task_active_pid_ns(struct task_struct *tsk)
 {
-	return tsk->nsproxy->pid_ns;
+	return pid_active_pid_ns(task_pid(tsk));
 }
 
 static inline struct task_struct *task_child_reaper(struct task_struct *tsk)
Index: lx26-21-mm2/kernel/nsproxy.c
===================================================================
--- lx26-21-mm2.orig/kernel/nsproxy.c	2007-05-22 16:58:37.000000000 -0700
+++ lx26-21-mm2/kernel/nsproxy.c	2007-05-22 16:59:50.000000000 -0700
@@ -19,7 +19,6 @@
 #include <linux/init_task.h>
 #include <linux/mnt_namespace.h>
 #include <linux/utsname.h>
-#include <linux/pid_namespace.h>
 
 struct nsproxy init_nsproxy = INIT_NSPROXY(init_nsproxy);
 
@@ -75,15 +74,8 @@ static struct nsproxy *create_new_namesp
 	if (IS_ERR(new_nsp->ipc_ns))
 		goto out_ipc;
 
-	new_nsp->pid_ns = copy_pid_ns(flags, tsk->nsproxy->pid_ns);
-	if (IS_ERR(new_nsp->pid_ns))
-		goto out_pid;
-
 	return new_nsp;
 
-out_pid:
-	if (new_nsp->ipc_ns)
-		put_ipc_ns(new_nsp->ipc_ns);
 out_ipc:
 	if (new_nsp->uts_ns)
 		put_uts_ns(new_nsp->uts_ns);
@@ -138,8 +130,6 @@ void free_nsproxy(struct nsproxy *ns)
 		put_uts_ns(ns->uts_ns);
 	if (ns->ipc_ns)
 		put_ipc_ns(ns->ipc_ns);
-	if (ns->pid_ns)
-		put_pid_ns(ns->pid_ns);
 	kfree(ns);
 }
 
Index: lx26-21-mm2/kernel/pid.c
===================================================================
--- lx26-21-mm2.orig/kernel/pid.c	2007-05-22 16:59:49.000000000 -0700
+++ lx26-21-mm2/kernel/pid.c	2007-05-22 16:59:50.000000000 -0700
@@ -242,6 +242,22 @@ static int init_upid(struct upid *upid, 
 	return 0;
 }
 
+static struct upid *pid_active_upid(struct pid *pid)
+{
+	return &pid->upid_list[0];
+}
+
+/*
+ * Return the active pid namespace of the process @pid.
+ *
+ * Note: At present, there is only one pid namespace (init_pid_ns).
+ */
+struct pid_namespace *pid_active_pid_ns(struct pid *pid)
+{
+	return pid_active_upid(pid)->pid_ns;
+}
+EXPORT_SYMBOL_GPL(pid_active_pid_ns);
+
 /*
  * Return the pid_t by which the process @pid is known in the pid
  * namespace @ns.
@@ -515,13 +531,6 @@ struct pid *find_ge_pid(int nr)
 }
 EXPORT_SYMBOL_GPL(find_get_pid);
 
-struct pid_namespace *copy_pid_ns(int flags, struct pid_namespace *old_ns)
-{
-	BUG_ON(!old_ns);
-	get_pid_ns(old_ns);
-	return old_ns;
-}
-
 void free_pid_ns(struct kref *kref)
 {
 	struct pid_namespace *ns;
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