sysctl: make kernel.ns_last_pid control dependent on CHECKPOINT_RESTORE

For those who doesn't need C/R functionality there is no need to control
last pid, ie the pid for the next fork() call.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/pid_namespace.c

@@ -196,6 +196,7 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns)
 	return;
 }
 
+#ifdef CONFIG_CHECKPOINT_RESTORE
 static int pid_ns_ctl_handler(struct ctl_table *table, int write,
 		void __user *buffer, size_t *lenp, loff_t *ppos)
 {
@@ -223,8 +224,8 @@ static struct ctl_table pid_ns_ctl_table[] = {
 	},
 	{ }
 };
-
 static struct ctl_path kern_path[] = { { .procname = "kernel", }, { } };
+#endif	/* CONFIG_CHECKPOINT_RESTORE */
 
 int reboot_pid_ns(struct pid_namespace *pid_ns, int cmd)
 {
@@ -258,7 +259,10 @@ int reboot_pid_ns(struct pid_namespace *pid_ns, int cmd)
 static __init int pid_namespaces_init(void)
 {
 	pid_ns_cachep = KMEM_CACHE(pid_namespace, SLAB_PANIC);
+
+#ifdef CONFIG_CHECKPOINT_RESTORE
 	register_sysctl_paths(kern_path, pid_ns_ctl_table);
+#endif
 	return 0;
 }