#ifndef _LINUX_NSPROXY_H
  #define _LINUX_NSPROXY_H
  
  #include <linux/spinlock.h>
  #include <linux/sched.h>

  struct mnt_namespace;

  struct uts_namespace;

  struct ipc_namespace;

  struct pid_namespace;

  struct fs_struct;

  /*
   * A structure to contain pointers to all per-process
   * namespaces - fs (mount), uts, network, sysvipc, etc.
   *
   * 'count' is the number of tasks holding a reference.
   * The count for each namespace, then, will be the number
   * of nsproxies pointing to it, not the number of tasks.
   *
   * The nsproxy is shared by tasks which share all namespaces.
   * As soon as a single namespace is cloned or unshared, the
   * nsproxy is copied.
   */
  struct nsproxy {
  	atomic_t count;

  	struct uts_namespace *uts_ns;

  	struct ipc_namespace *ipc_ns;

  	struct mnt_namespace *mnt_ns;

  	struct pid_namespace *pid_ns;

  	struct net 	     *net_ns;

  };
  extern struct nsproxy init_nsproxy;

  /*
   * the namespaces access rules are:
   *
   *  1. only current task is allowed to change tsk->nsproxy pointer or
   *     any pointer on the nsproxy itself
   *
   *  2. when accessing (i.e. reading) current task's namespaces - no
   *     precautions should be taken - just dereference the pointers
   *
   *  3. the access to other task namespaces is performed like this
   *     rcu_read_lock();
   *     nsproxy = task_nsproxy(tsk);
   *     if (nsproxy != NULL) {
   *             / *
   *               * work with the namespaces here
   *               * e.g. get the reference on one of them
   *               * /
   *     } / *
   *         * NULL task_nsproxy() means that this task is
   *         * almost dead (zombie)
   *         * /
   *     rcu_read_unlock();
   *
   */
  
  static inline struct nsproxy *task_nsproxy(struct task_struct *tsk)
  {
  	return rcu_dereference(tsk->nsproxy);
  }

  int copy_namespaces(unsigned long flags, struct task_struct *tsk);

  void exit_task_namespaces(struct task_struct *tsk);
  void switch_task_namespaces(struct task_struct *tsk, struct nsproxy *new);

  void free_nsproxy(struct nsproxy *ns);

  int unshare_nsproxy_namespaces(unsigned long, struct nsproxy **,
  	struct fs_struct *);

  int __init nsproxy_cache_init(void);

  static inline void put_nsproxy(struct nsproxy *ns)

  {

  	if (atomic_dec_and_test(&ns->count)) {

  		free_nsproxy(ns);

  	}

  }

  static inline void get_nsproxy(struct nsproxy *ns)

  {

  	atomic_inc(&ns->count);

  }

  #endif