+#ifndef _LINUX_PID_NS_H
+#define _LINUX_PID_NS_H
+
+#include <linux/sched.h>
+#include <linux/mm.h>
+#include <linux/threads.h>
+#include <linux/pid.h>
+#include <linux/nsproxy.h>
+#include <linux/kref.h>
+
+struct pidmap {
+ atomic_t nr_free;
+ void *page;
+};
+
+#define PIDMAP_ENTRIES ((PID_MAX_LIMIT + 8*PAGE_SIZE - 1)/PAGE_SIZE/8)
+
+struct pid_namespace {
+ struct kref kref;
+ struct pidmap pidmap[PIDMAP_ENTRIES];
+ int last_pid;
+ struct task_struct *child_reaper;
+};
+
+extern struct pid_namespace init_pid_ns;
+
+static inline void get_pid_ns(struct pid_namespace *ns)
+{
+ kref_get(&ns->kref);
+}
+
+extern int copy_pid_ns(int flags, struct task_struct *tsk);
+extern void free_pid_ns(struct kref *kref);
+
+static inline void put_pid_ns(struct pid_namespace *ns)
+{
+ kref_put(&ns->kref, free_pid_ns);
+}
+
+static inline struct task_struct *child_reaper(struct task_struct *tsk)
+{
+ return init_pid_ns.child_reaper;
+}
+
+#endif /* _LINUX_PID_NS_H */