linux/include/linux/nsproxy.h
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   1#ifndef _LINUX_NSPROXY_H
   2#define _LINUX_NSPROXY_H
   3
   4#include <linux/spinlock.h>
   5#include <linux/sched.h>
   6
   7struct mnt_namespace;
   8struct uts_namespace;
   9struct ipc_namespace;
  10struct pid_namespace;
  11struct fs_struct;
  12
  13/*
  14 * A structure to contain pointers to all per-process
  15 * namespaces - fs (mount), uts, network, sysvipc, etc.
  16 *
  17 * 'count' is the number of tasks holding a reference.
  18 * The count for each namespace, then, will be the number
  19 * of nsproxies pointing to it, not the number of tasks.
  20 *
  21 * The nsproxy is shared by tasks which share all namespaces.
  22 * As soon as a single namespace is cloned or unshared, the
  23 * nsproxy is copied.
  24 */
  25struct nsproxy {
  26        atomic_t count;
  27        struct uts_namespace *uts_ns;
  28        struct ipc_namespace *ipc_ns;
  29        struct mnt_namespace *mnt_ns;
  30        struct pid_namespace *pid_ns;
  31        struct net           *net_ns;
  32};
  33extern struct nsproxy init_nsproxy;
  34
  35/*
  36 * the namespaces access rules are:
  37 *
  38 *  1. only current task is allowed to change tsk->nsproxy pointer or
  39 *     any pointer on the nsproxy itself
  40 *
  41 *  2. when accessing (i.e. reading) current task's namespaces - no
  42 *     precautions should be taken - just dereference the pointers
  43 *
  44 *  3. the access to other task namespaces is performed like this
  45 *     rcu_read_lock();
  46 *     nsproxy = task_nsproxy(tsk);
  47 *     if (nsproxy != NULL) {
  48 *             / *
  49 *               * work with the namespaces here
  50 *               * e.g. get the reference on one of them
  51 *               * /
  52 *     } / *
  53 *         * NULL task_nsproxy() means that this task is
  54 *         * almost dead (zombie)
  55 *         * /
  56 *     rcu_read_unlock();
  57 *
  58 */
  59
  60static inline struct nsproxy *task_nsproxy(struct task_struct *tsk)
  61{
  62        return rcu_dereference(tsk->nsproxy);
  63}
  64
  65int copy_namespaces(unsigned long flags, struct task_struct *tsk);
  66void exit_task_namespaces(struct task_struct *tsk);
  67void switch_task_namespaces(struct task_struct *tsk, struct nsproxy *new);
  68void free_nsproxy(struct nsproxy *ns);
  69int unshare_nsproxy_namespaces(unsigned long, struct nsproxy **,
  70        struct fs_struct *);
  71int __init nsproxy_cache_init(void);
  72
  73static inline void put_nsproxy(struct nsproxy *ns)
  74{
  75        if (atomic_dec_and_test(&ns->count)) {
  76                free_nsproxy(ns);
  77        }
  78}
  79
  80static inline void get_nsproxy(struct nsproxy *ns)
  81{
  82        atomic_inc(&ns->count);
  83}
  84
  85#endif
  86
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