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Linus Torvalds1da177e2005-04-16 15:20:36 -07001#ifndef _LINUX_PID_H
2#define _LINUX_PID_H
3
Eric W. Biederman92476d72006-03-31 02:31:42 -08004#include <linux/rcupdate.h>
5
Linus Torvalds1da177e2005-04-16 15:20:36 -07006enum pid_type
7{
8 PIDTYPE_PID,
Linus Torvalds1da177e2005-04-16 15:20:36 -07009 PIDTYPE_PGID,
10 PIDTYPE_SID,
11 PIDTYPE_MAX
12};
13
Eric W. Biederman92476d72006-03-31 02:31:42 -080014/*
15 * What is struct pid?
16 *
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.
23 *
24 * Storing pid_t values in the kernel and refering 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.
28 *
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.
35 *
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
Sukadev Bhattiprolu84d73782006-12-08 02:38:01 -080038 * 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
40 * processes.
Eric W. Biederman92476d72006-03-31 02:31:42 -080041 */
42
Sukadev Bhattiprolu4c3f2ea2007-10-18 23:40:03 -070043
44/*
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.
48 */
49
50struct upid {
51 /* Try to keep pid_chain in the same cacheline as nr for find_pid */
52 int nr;
53 struct pid_namespace *ns;
54 struct hlist_node pid_chain;
55};
56
Linus Torvalds1da177e2005-04-16 15:20:36 -070057struct pid
58{
Eric W. Biederman92476d72006-03-31 02:31:42 -080059 atomic_t count;
Eric W. Biederman92476d72006-03-31 02:31:42 -080060 /* lists of tasks that use this pid */
61 struct hlist_head tasks[PIDTYPE_MAX];
62 struct rcu_head rcu;
Pavel Emelyanovcaafa432008-04-30 00:54:31 -070063 unsigned int level;
Sukadev Bhattiprolu4c3f2ea2007-10-18 23:40:03 -070064 struct upid numbers[1];
Linus Torvalds1da177e2005-04-16 15:20:36 -070065};
66
Sukadev Bhattiprolu820e45d2007-05-10 22:23:00 -070067extern struct pid init_struct_pid;
68
Eric W. Biederman92476d72006-03-31 02:31:42 -080069struct pid_link
70{
71 struct hlist_node node;
72 struct pid *pid;
73};
74
75static inline struct pid *get_pid(struct pid *pid)
76{
77 if (pid)
78 atomic_inc(&pid->count);
79 return pid;
80}
81
Harvey Harrisonb3c97522008-02-13 15:03:15 -080082extern void put_pid(struct pid *pid);
83extern struct task_struct *pid_task(struct pid *pid, enum pid_type);
84extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type);
Linus Torvalds1da177e2005-04-16 15:20:36 -070085
Oleg Nesterov1a657f72006-10-02 02:18:59 -070086extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
87
Linus Torvalds1da177e2005-04-16 15:20:36 -070088/*
89 * attach_pid() and detach_pid() must be called with the tasklist_lock
90 * write-held.
91 */
Oleg Nesterov24336ea2008-04-30 00:54:26 -070092extern void attach_pid(struct task_struct *task, enum pid_type type,
93 struct pid *pid);
Harvey Harrisonb3c97522008-02-13 15:03:15 -080094extern void detach_pid(struct task_struct *task, enum pid_type);
Oleg Nesterov24336ea2008-04-30 00:54:26 -070095extern void change_pid(struct task_struct *task, enum pid_type,
96 struct pid *pid);
Harvey Harrisonb3c97522008-02-13 15:03:15 -080097extern void transfer_pid(struct task_struct *old, struct task_struct *new,
98 enum pid_type);
Linus Torvalds1da177e2005-04-16 15:20:36 -070099
Pavel Emelyanov198fe212007-10-18 23:40:06 -0700100struct pid_namespace;
101extern struct pid_namespace init_pid_ns;
102
Linus Torvalds1da177e2005-04-16 15:20:36 -0700103/*
104 * look up a PID in the hash table. Must be called with the tasklist_lock
Eric W. Biederman92476d72006-03-31 02:31:42 -0800105 * or rcu_read_lock() held.
Pavel Emelyanov198fe212007-10-18 23:40:06 -0700106 *
107 * find_pid_ns() finds the pid in the namespace specified
108 * find_pid() find the pid by its global id, i.e. in the init namespace
109 * find_vpid() finr the pid by its virtual id, i.e. in the current namespace
110 *
111 * see also find_task_by_pid() set in include/linux/sched.h
Linus Torvalds1da177e2005-04-16 15:20:36 -0700112 */
Harvey Harrisonb3c97522008-02-13 15:03:15 -0800113extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns);
Pavel Emelyanov89905712007-10-18 23:40:19 -0700114extern struct pid *find_vpid(int nr);
115extern struct pid *find_pid(int nr);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700116
Eric W. Biederman92476d72006-03-31 02:31:42 -0800117/*
118 * Lookup a PID in the hash table, and return with it's count elevated.
119 */
120extern struct pid *find_get_pid(int nr);
Pavel Emelyanov198fe212007-10-18 23:40:06 -0700121extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
Pavel Emelyanov74bd59b2008-02-08 04:18:24 -0800122int next_pidmap(struct pid_namespace *pid_ns, int last);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700123
Pavel Emelyanov8ef047a2007-10-18 23:40:05 -0700124extern struct pid *alloc_pid(struct pid_namespace *ns);
Harvey Harrisonb3c97522008-02-13 15:03:15 -0800125extern void free_pid(struct pid *pid);
Eric W. Biederman92476d72006-03-31 02:31:42 -0800126
Pavel Emelyanov7af57292007-10-18 23:40:06 -0700127/*
128 * the helpers to get the pid's id seen from different namespaces
129 *
130 * pid_nr() : global id, i.e. the id seen from the init namespace;
Eric W. Biederman44c4e1b2008-02-08 04:19:15 -0800131 * pid_vnr() : virtual id, i.e. the id seen from the pid namespace of
132 * current.
Pavel Emelyanov7af57292007-10-18 23:40:06 -0700133 * pid_nr_ns() : id seen from the ns specified.
134 *
135 * see also task_xid_nr() etc in include/linux/sched.h
136 */
137
Eric W. Biederman5feb8f52006-10-02 02:17:12 -0700138static inline pid_t pid_nr(struct pid *pid)
139{
140 pid_t nr = 0;
141 if (pid)
Pavel Emelyanov7af57292007-10-18 23:40:06 -0700142 nr = pid->numbers[0].nr;
143 return nr;
144}
145
146pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
Eric W. Biederman44c4e1b2008-02-08 04:19:15 -0800147pid_t pid_vnr(struct pid *pid);
Eric W. Biederman5feb8f52006-10-02 02:17:12 -0700148
Andrew Morton1d328492006-10-03 01:13:45 -0700149#define do_each_pid_task(pid, type, task) \
150 do { \
151 struct hlist_node *pos___; \
152 if (pid != NULL) \
153 hlist_for_each_entry_rcu((task), pos___, \
Oleg Nesterovd387cae2006-10-02 02:17:22 -0700154 &pid->tasks[type], pids[type].node) {
Linus Torvalds1da177e2005-04-16 15:20:36 -0700155
Oleg Nesterov46f382d2008-02-08 04:19:19 -0800156 /*
157 * Both old and new leaders may be attached to
158 * the same pid in the middle of de_thread().
159 */
Andrew Morton1d328492006-10-03 01:13:45 -0700160#define while_each_pid_task(pid, type, task) \
Oleg Nesterov46f382d2008-02-08 04:19:19 -0800161 if (type == PIDTYPE_PID) \
162 break; \
Andrew Morton1d328492006-10-03 01:13:45 -0700163 } \
Oleg Nesterovd387cae2006-10-02 02:17:22 -0700164 } while (0)
Eric W. Biederman558cb322006-10-02 02:17:09 -0700165
Linus Torvalds1da177e2005-04-16 15:20:36 -0700166#endif /* _LINUX_PID_H */