4 #include <linux/rcupdate.h>
17 * A struct pid is the kernel's internal notion of a process identifier.
18 * It refers to individual tasks, process groups, and sessions. While
19 * there are processes attached to it the struct pid lives in a hash
20 * table, so it and then the processes that it refers to can be found
21 * quickly from the numeric pid value. The attached processes may be
22 * quickly accessed by following pointers from struct pid.
24 * Storing pid_t values in the kernel and referring to them later has a
25 * problem. The process originally with that pid may have exited and the
26 * pid allocator wrapped, and another process could have come along
27 * and been assigned that pid.
29 * Referring to user space processes by holding a reference to struct
30 * task_struct has a problem. When the user space process exits
31 * the now useless task_struct is still kept. A task_struct plus a
32 * stack consumes around 10K of low kernel memory. More precisely
33 * this is THREAD_SIZE + sizeof(struct task_struct). By comparison
34 * a struct pid is about 64 bytes.
36 * Holding a reference to struct pid solves both of these problems.
37 * It is small so holding a reference does not consume a lot of
38 * resources, and since a new struct pid is allocated when the numeric pid
39 * value is reused (when pids wrap around) we don't mistakenly refer to new
45 * struct upid is used to get the id of the struct pid, as it is
46 * seen in particular namespace. Later the struct pid is found with
47 * find_pid_ns() using the int nr and struct pid_namespace *ns.
51 /* Try to keep pid_chain in the same cacheline as nr for find_vpid */
53 struct pid_namespace
*ns
;
54 struct hlist_node pid_chain
;
61 /* lists of tasks that use this pid */
62 struct hlist_head tasks
[PIDTYPE_MAX
];
64 struct upid numbers
[1];
67 extern struct pid init_struct_pid
;
71 struct hlist_node node
;
75 static inline struct pid
*get_pid(struct pid
*pid
)
78 atomic_inc(&pid
->count
);
82 extern void put_pid(struct pid
*pid
);
83 extern struct task_struct
*pid_task(struct pid
*pid
, enum pid_type
);
84 extern struct task_struct
*get_pid_task(struct pid
*pid
, enum pid_type
);
86 extern struct pid
*get_task_pid(struct task_struct
*task
, enum pid_type type
);
89 * these helpers must be called with the tasklist_lock write-held.
91 extern void attach_pid(struct task_struct
*task
, enum pid_type
);
92 extern void detach_pid(struct task_struct
*task
, enum pid_type
);
93 extern void change_pid(struct task_struct
*task
, enum pid_type
,
95 extern void transfer_pid(struct task_struct
*old
, struct task_struct
*new,
99 extern struct pid_namespace init_pid_ns
;
102 * look up a PID in the hash table. Must be called with the tasklist_lock
103 * or rcu_read_lock() held.
105 * find_pid_ns() finds the pid in the namespace specified
106 * find_vpid() finds the pid by its virtual id, i.e. in the current namespace
108 * see also find_task_by_vpid() set in include/linux/sched.h
110 extern struct pid
*find_pid_ns(int nr
, struct pid_namespace
*ns
);
111 extern struct pid
*find_vpid(int nr
);
114 * Lookup a PID in the hash table, and return with it's count elevated.
116 extern struct pid
*find_get_pid(int nr
);
117 extern struct pid
*find_ge_pid(int nr
, struct pid_namespace
*);
118 int next_pidmap(struct pid_namespace
*pid_ns
, unsigned int last
);
120 extern struct pid
*alloc_pid(struct pid_namespace
*ns
);
121 extern void free_pid(struct pid
*pid
);
122 extern void disable_pid_allocation(struct pid_namespace
*ns
);
125 * ns_of_pid() returns the pid namespace in which the specified pid was
129 * ns_of_pid() is expected to be called for a process (task) that has
130 * an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid
131 * is expected to be non-NULL. If @pid is NULL, caller should handle
132 * the resulting NULL pid-ns.
134 static inline struct pid_namespace
*ns_of_pid(struct pid
*pid
)
136 struct pid_namespace
*ns
= NULL
;
138 ns
= pid
->numbers
[pid
->level
].ns
;
143 * is_child_reaper returns true if the pid is the init process
144 * of the current namespace. As this one could be checked before
145 * pid_ns->child_reaper is assigned in copy_process, we check
146 * with the pid number.
148 static inline bool is_child_reaper(struct pid
*pid
)
150 return pid
->numbers
[pid
->level
].nr
== 1;
154 * the helpers to get the pid's id seen from different namespaces
156 * pid_nr() : global id, i.e. the id seen from the init namespace;
157 * pid_vnr() : virtual id, i.e. the id seen from the pid namespace of
159 * pid_nr_ns() : id seen from the ns specified.
161 * see also task_xid_nr() etc in include/linux/sched.h
164 static inline pid_t
pid_nr(struct pid
*pid
)
168 nr
= pid
->numbers
[0].nr
;
172 pid_t
pid_nr_ns(struct pid
*pid
, struct pid_namespace
*ns
);
173 pid_t
pid_vnr(struct pid
*pid
);
175 #define do_each_pid_task(pid, type, task) \
178 hlist_for_each_entry_rcu((task), \
179 &(pid)->tasks[type], pids[type].node) {
182 * Both old and new leaders may be attached to
183 * the same pid in the middle of de_thread().
185 #define while_each_pid_task(pid, type, task) \
186 if (type == PIDTYPE_PID) \
191 #define do_each_pid_thread(pid, type, task) \
192 do_each_pid_task(pid, type, task) { \
193 struct task_struct *tg___ = task; \
196 #define while_each_pid_thread(pid, type, task) \
197 } while_each_thread(tg___, task); \
199 } while_each_pid_task(pid, type, task)
200 #endif /* _LINUX_PID_H */