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
39 * pid value is reused we don't mistakenly refer to new processes.
40 */
41
42struct pid
43{
44 atomic_t count;
45 /* Try to keep pid_chain in the same cacheline as nr for find_pid */
46 int nr;
47 struct hlist_node pid_chain;
48 /* lists of tasks that use this pid */
49 struct hlist_head tasks[PIDTYPE_MAX];
50 struct rcu_head rcu;
51};
52
53struct 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));
70
71extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
72
73/*
74 * attach_pid() and detach_pid() must be called with the tasklist_lock
75 * write-held.
76 */
77extern int FASTCALL(attach_pid(struct task_struct *task,
78 enum pid_type type, int nr));
79
80extern void FASTCALL(detach_pid(struct task_struct *task, enum pid_type));
81extern void FASTCALL(transfer_pid(struct task_struct *old,
82 struct task_struct *new, enum pid_type));
83
84/*
85 * look up a PID in the hash table. Must be called with the tasklist_lock
86 * or rcu_read_lock() held.
87 */
88extern struct pid *FASTCALL(find_pid(int nr));
89
90/*
91 * Lookup a PID in the hash table, and return with it's count elevated.
92 */
93extern struct pid *find_get_pid(int nr);
94extern struct pid *find_ge_pid(int nr);
95
96extern struct pid *alloc_pid(void);
97extern void FASTCALL(free_pid(struct pid *pid));
98
99static inline pid_t pid_nr(struct pid *pid)
100{
101 pid_t nr = 0;
102 if (pid)
103 nr = pid->nr;
104 return nr;
105}
106
107
108#define do_each_task_pid(who, type, task) \
109 do { \
110 struct hlist_node *pos___; \
111 struct pid *pid___ = find_pid(who); \
112 if (pid___ != NULL) \
113 hlist_for_each_entry_rcu((task), pos___, \
114 &pid___->tasks[type], pids[type].node) {
115
116#define while_each_task_pid(who, type, task) \
117 } \
118 } while (0)
119
120
121#define do_each_pid_task(pid, type, task) \
122 do { \
123 struct hlist_node *pos___; \
124 if (pid != NULL) \
125 hlist_for_each_entry_rcu((task), pos___, \
126 &pid->tasks[type], pids[type].node) {
127
128#define while_each_pid_task(pid, type, task) \
129 } \
130 } while (0)
131
132#endif /* _LINUX_PID_H */