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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
38 * resources, and since a new struct pid is allocated when the numeric
39 * pid value is reused we don't mistakenly refer to new processes.
40 */
41
Linus Torvalds1da177e2005-04-16 15:20:36 -070042struct pid
43{
Eric W. Biederman92476d72006-03-31 02:31:42 -080044 atomic_t count;
Linus Torvalds1da177e2005-04-16 15:20:36 -070045 /* Try to keep pid_chain in the same cacheline as nr for find_pid */
46 int nr;
47 struct hlist_node pid_chain;
Eric W. Biederman92476d72006-03-31 02:31:42 -080048 /* lists of tasks that use this pid */
49 struct hlist_head tasks[PIDTYPE_MAX];
50 struct rcu_head rcu;
Linus Torvalds1da177e2005-04-16 15:20:36 -070051};
52
Eric W. Biederman92476d72006-03-31 02:31:42 -080053struct pid_link
54{
55 struct hlist_node node;
56 struct pid *pid;
57};
58
59static inline struct pid *get_pid(struct pid *pid)
60{
61 if (pid)
62 atomic_inc(&pid->count);
63 return pid;
64}
65
66extern void FASTCALL(put_pid(struct pid *pid));
67extern struct task_struct *FASTCALL(pid_task(struct pid *pid, enum pid_type));
68extern struct task_struct *FASTCALL(get_pid_task(struct pid *pid,
69 enum pid_type));
Linus Torvalds1da177e2005-04-16 15:20:36 -070070
71/*
72 * attach_pid() and detach_pid() must be called with the tasklist_lock
73 * write-held.
74 */
Eric W. Biederman92476d72006-03-31 02:31:42 -080075extern int FASTCALL(attach_pid(struct task_struct *task,
76 enum pid_type type, int nr));
Linus Torvalds1da177e2005-04-16 15:20:36 -070077
78extern void FASTCALL(detach_pid(struct task_struct *task, enum pid_type));
Eric W. Biedermanc18258c2006-09-27 01:51:06 -070079extern void FASTCALL(transfer_pid(struct task_struct *old,
80 struct task_struct *new, enum pid_type));
Linus Torvalds1da177e2005-04-16 15:20:36 -070081
82/*
83 * look up a PID in the hash table. Must be called with the tasklist_lock
Eric W. Biederman92476d72006-03-31 02:31:42 -080084 * or rcu_read_lock() held.
Linus Torvalds1da177e2005-04-16 15:20:36 -070085 */
Eric W. Biederman92476d72006-03-31 02:31:42 -080086extern struct pid *FASTCALL(find_pid(int nr));
Linus Torvalds1da177e2005-04-16 15:20:36 -070087
Eric W. Biederman92476d72006-03-31 02:31:42 -080088/*
89 * Lookup a PID in the hash table, and return with it's count elevated.
90 */
91extern struct pid *find_get_pid(int nr);
Eric W. Biederman0804ef42006-10-02 02:17:04 -070092extern struct pid *find_ge_pid(int nr);
Linus Torvalds1da177e2005-04-16 15:20:36 -070093
Eric W. Biederman92476d72006-03-31 02:31:42 -080094extern struct pid *alloc_pid(void);
95extern void FASTCALL(free_pid(struct pid *pid));
96
Eric W. Biederman5feb8f52006-10-02 02:17:12 -070097static inline pid_t pid_nr(struct pid *pid)
98{
99 pid_t nr = 0;
100 if (pid)
101 nr = pid->nr;
102 return nr;
103}
104
Eric W. Biederman92476d72006-03-31 02:31:42 -0800105#define pid_next(task, type) \
106 ((task)->pids[(type)].node.next)
107
108#define pid_next_task(task, type) \
109 hlist_entry(pid_next(task, type), struct task_struct, \
110 pids[(type)].node)
111
112
113/* We could use hlist_for_each_entry_rcu here but it takes more arguments
114 * than the do_each_task_pid/while_each_task_pid. So we roll our own
115 * to preserve the existing interface.
116 */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700117#define do_each_task_pid(who, type, task) \
118 if ((task = find_task_by_pid_type(type, who))) { \
Eric W. Biederman92476d72006-03-31 02:31:42 -0800119 prefetch(pid_next(task, type)); \
Linus Torvalds1da177e2005-04-16 15:20:36 -0700120 do {
121
122#define while_each_task_pid(who, type, task) \
Eric W. Biederman92476d72006-03-31 02:31:42 -0800123 } while (pid_next(task, type) && ({ \
124 task = pid_next_task(task, type); \
125 rcu_dereference(task); \
126 prefetch(pid_next(task, type)); \
127 1; }) ); \
128 }
Linus Torvalds1da177e2005-04-16 15:20:36 -0700129
Eric W. Biederman558cb322006-10-02 02:17:09 -0700130#define do_each_pid_task(pid, type, task) \
131 if ((task = pid_task(pid, type))) { \
132 prefetch(pid_next(task, type)); \
133 do {
134
135#define while_each_pid_task(pid, type, task) \
136 } while (pid_next(task, type) && ({ \
137 task = pid_next_task(task, type); \
138 rcu_dereference(task); \
139 prefetch(pid_next(task, type)); \
140 1; }) ); \
141 }
142
Linus Torvalds1da177e2005-04-16 15:20:36 -0700143#endif /* _LINUX_PID_H */