text: /* SPDX-License-Identifier: GPL-2.0 */
  #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 cgroup_namespace;
  struct fs_struct;
  
  /*
   * A structure to contain pointers to all per-process
   * namespaces - fs (mount), uts, network, sysvipc, etc.
   *
   * The pid namespace is an exception -- it's accessed using
   * task_active_pid_ns.  The pid namespace here is the
   * namespace that children will use.
   *
   * '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_for_children;
  	struct net 	     *net_ns;
  	struct time_namespace *time_ns;
  	struct time_namespace *time_ns_for_children;
  	struct cgroup_namespace *cgroup_ns;
  };
  extern struct nsproxy init_nsproxy;
  
  /*
   * A structure to encompass all bits needed to install
   * a partial or complete new set of namespaces.
   *
   * If a new user namespace is requested cred will
   * point to a modifiable set of credentials. If a pointer
   * to a modifiable set is needed nsset_cred() must be
   * used and tested.
   */
  struct nsset {
  	unsigned flags;
  	struct nsproxy *nsproxy;
  	struct fs_struct *fs;
  	const struct cred *cred;
  };
  
  static inline struct cred *nsset_cred(struct nsset *set)
  {
  	if (set->flags & CLONE_NEWUSER)
  		return (struct cred *)set->cred;
  
  	return NULL;
  }
  
  /*
   * the namespaces access rules are:
   *
   *  1. only current task is allowed to change tsk->nsproxy pointer or
   *     any pointer on the nsproxy itself.  Current must hold the task_lock
   *     when changing tsk->nsproxy.
   *
   *  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
   *     task_lock(task);
   *     nsproxy = task->nsproxy;
   *     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)
   *         * /
   *     task_unlock(task);
   *
   */
  
  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 cred *, 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
  