#ifndef _LINUX_USER_NAMESPACE_H
  #define _LINUX_USER_NAMESPACE_H
  
  #include <linux/kref.h>
  #include <linux/nsproxy.h>
  #include <linux/sched.h>

  #include <linux/err.h>

  #define UIDHASH_BITS	(CONFIG_BASE_SMALL ? 3 : 7)

  #define UIDHASH_SZ	(1 << UIDHASH_BITS)
  
  struct user_namespace {
  	struct kref		kref;

  	struct hlist_head	uidhash_table[UIDHASH_SZ];

  	struct user_struct	*creator;

  	struct work_struct	destroyer;

  };
  
  extern struct user_namespace init_user_ns;
  
  #ifdef CONFIG_USER_NS
  
  static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
  {
  	if (ns)
  		kref_get(&ns->kref);
  	return ns;
  }

  extern int create_user_ns(struct cred *new);

  extern void free_user_ns(struct kref *kref);
  
  static inline void put_user_ns(struct user_namespace *ns)
  {
  	if (ns)
  		kref_put(&ns->kref, free_user_ns);
  }

  uid_t user_ns_map_uid(struct user_namespace *to, const struct cred *cred, uid_t uid);
  gid_t user_ns_map_gid(struct user_namespace *to, const struct cred *cred, gid_t gid);

  #else
  
  static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
  {
  	return &init_user_ns;
  }

  static inline int create_user_ns(struct cred *new)

  {

  	return -EINVAL;

  }
  
  static inline void put_user_ns(struct user_namespace *ns)
  {
  }

  static inline uid_t user_ns_map_uid(struct user_namespace *to,
  	const struct cred *cred, uid_t uid)
  {
  	return uid;
  }
  static inline gid_t user_ns_map_gid(struct user_namespace *to,
  	const struct cred *cred, gid_t gid)
  {
  	return gid;
  }

  #endif
  
  #endif /* _LINUX_USER_H */