Linux kernel mirror (for testing)
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linux
1#ifndef _LINUX_PID_H
2#define _LINUX_PID_H
3
4#include <linux/rcupdate.h>
5
6enum pid_type
7{
8 PIDTYPE_PID,
9 PIDTYPE_PGID,
10 PIDTYPE_SID,
11 PIDTYPE_MAX
12};
13
14/*
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 pid
39 * value is reused (when pids wrap around) we don't mistakenly refer to new
40 * processes.
41 */
42
43struct pid
44{
45 atomic_t count;
46 /* Try to keep pid_chain in the same cacheline as nr for find_pid */
47 int nr;
48 struct hlist_node pid_chain;
49 /* lists of tasks that use this pid */
50 struct hlist_head tasks[PIDTYPE_MAX];
51 struct rcu_head rcu;
52};
53
54struct pid_link
55{
56 struct hlist_node node;
57 struct pid *pid;
58};
59
60static inline struct pid *get_pid(struct pid *pid)
61{
62 if (pid)
63 atomic_inc(&pid->count);
64 return pid;
65}
66
67extern void FASTCALL(put_pid(struct pid *pid));
68extern struct task_struct *FASTCALL(pid_task(struct pid *pid, enum pid_type));
69extern struct task_struct *FASTCALL(get_pid_task(struct pid *pid,
70 enum pid_type));
71
72extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
73
74/*
75 * attach_pid() and detach_pid() must be called with the tasklist_lock
76 * write-held.
77 */
78extern int FASTCALL(attach_pid(struct task_struct *task,
79 enum pid_type type, int nr));
80
81extern void FASTCALL(detach_pid(struct task_struct *task, enum pid_type));
82extern void FASTCALL(transfer_pid(struct task_struct *old,
83 struct task_struct *new, enum pid_type));
84
85/*
86 * look up a PID in the hash table. Must be called with the tasklist_lock
87 * or rcu_read_lock() held.
88 */
89extern struct pid *FASTCALL(find_pid(int nr));
90
91/*
92 * Lookup a PID in the hash table, and return with it's count elevated.
93 */
94extern struct pid *find_get_pid(int nr);
95extern struct pid *find_ge_pid(int nr);
96
97extern struct pid *alloc_pid(void);
98extern void FASTCALL(free_pid(struct pid *pid));
99
100static inline pid_t pid_nr(struct pid *pid)
101{
102 pid_t nr = 0;
103 if (pid)
104 nr = pid->nr;
105 return nr;
106}
107
108
109#define do_each_task_pid(who, type, task) \
110 do { \
111 struct hlist_node *pos___; \
112 struct pid *pid___ = find_pid(who); \
113 if (pid___ != NULL) \
114 hlist_for_each_entry_rcu((task), pos___, \
115 &pid___->tasks[type], pids[type].node) {
116
117#define while_each_task_pid(who, type, task) \
118 } \
119 } while (0)
120
121
122#define do_each_pid_task(pid, type, task) \
123 do { \
124 struct hlist_node *pos___; \
125 if (pid != NULL) \
126 hlist_for_each_entry_rcu((task), pos___, \
127 &pid->tasks[type], pids[type].node) {
128
129#define while_each_pid_task(pid, type, task) \
130 } \
131 } while (0)
132
133#endif /* _LINUX_PID_H */