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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
Linus Torvalds1da177e2005-04-16 15:20:36 -070043struct pid
44{
Eric W. Biederman92476d72006-03-31 02:31:42 -080045 atomic_t count;
Linus Torvalds1da177e2005-04-16 15:20:36 -070046 /* Try to keep pid_chain in the same cacheline as nr for find_pid */
47 int nr;
48 struct hlist_node pid_chain;
Eric W. Biederman92476d72006-03-31 02:31:42 -080049 /* lists of tasks that use this pid */
50 struct hlist_head tasks[PIDTYPE_MAX];
51 struct rcu_head rcu;
Linus Torvalds1da177e2005-04-16 15:20:36 -070052};
53
Sukadev Bhattiprolu820e45d2007-05-10 22:23:00 -070054extern struct pid init_struct_pid;
55
Eric W. Biederman92476d72006-03-31 02:31:42 -080056struct pid_link
57{
58 struct hlist_node node;
59 struct pid *pid;
60};
61
62static inline struct pid *get_pid(struct pid *pid)
63{
64 if (pid)
65 atomic_inc(&pid->count);
66 return pid;
67}
68
69extern void FASTCALL(put_pid(struct pid *pid));
70extern struct task_struct *FASTCALL(pid_task(struct pid *pid, enum pid_type));
71extern struct task_struct *FASTCALL(get_pid_task(struct pid *pid,
72 enum pid_type));
Linus Torvalds1da177e2005-04-16 15:20:36 -070073
Oleg Nesterov1a657f782006-10-02 02:18:59 -070074extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
75
Linus Torvalds1da177e2005-04-16 15:20:36 -070076/*
77 * attach_pid() and detach_pid() must be called with the tasklist_lock
78 * write-held.
79 */
Eric W. Biederman92476d72006-03-31 02:31:42 -080080extern int FASTCALL(attach_pid(struct task_struct *task,
Sukadev Bhattiprolue713d0d2007-05-10 22:22:58 -070081 enum pid_type type, struct pid *pid));
Linus Torvalds1da177e2005-04-16 15:20:36 -070082extern void FASTCALL(detach_pid(struct task_struct *task, enum pid_type));
Eric W. Biedermanc18258c2006-09-27 01:51:06 -070083extern void FASTCALL(transfer_pid(struct task_struct *old,
84 struct task_struct *new, enum pid_type));
Linus Torvalds1da177e2005-04-16 15:20:36 -070085
86/*
87 * look up a PID in the hash table. Must be called with the tasklist_lock
Eric W. Biederman92476d72006-03-31 02:31:42 -080088 * or rcu_read_lock() held.
Linus Torvalds1da177e2005-04-16 15:20:36 -070089 */
Eric W. Biederman92476d72006-03-31 02:31:42 -080090extern struct pid *FASTCALL(find_pid(int nr));
Linus Torvalds1da177e2005-04-16 15:20:36 -070091
Eric W. Biederman92476d72006-03-31 02:31:42 -080092/*
93 * Lookup a PID in the hash table, and return with it's count elevated.
94 */
95extern struct pid *find_get_pid(int nr);
Eric W. Biederman0804ef42006-10-02 02:17:04 -070096extern struct pid *find_ge_pid(int nr);
Linus Torvalds1da177e2005-04-16 15:20:36 -070097
Eric W. Biederman92476d72006-03-31 02:31:42 -080098extern struct pid *alloc_pid(void);
99extern void FASTCALL(free_pid(struct pid *pid));
100
Eric W. Biederman5feb8f52006-10-02 02:17:12 -0700101static inline pid_t pid_nr(struct pid *pid)
102{
103 pid_t nr = 0;
104 if (pid)
105 nr = pid->nr;
106 return nr;
107}
108
Andrew Morton1d328492006-10-03 01:13:45 -0700109#define do_each_pid_task(pid, type, task) \
110 do { \
111 struct hlist_node *pos___; \
112 if (pid != NULL) \
113 hlist_for_each_entry_rcu((task), pos___, \
Oleg Nesterovd387cae2006-10-02 02:17:22 -0700114 &pid->tasks[type], pids[type].node) {
Linus Torvalds1da177e2005-04-16 15:20:36 -0700115
Andrew Morton1d328492006-10-03 01:13:45 -0700116#define while_each_pid_task(pid, type, task) \
117 } \
Oleg Nesterovd387cae2006-10-02 02:17:22 -0700118 } while (0)
Eric W. Biederman558cb322006-10-02 02:17:09 -0700119
Linus Torvalds1da177e2005-04-16 15:20:36 -0700120#endif /* _LINUX_PID_H */