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
43
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
57struct pid
58{
59 atomic_t count;
60 /* lists of tasks that use this pid */
61 struct hlist_head tasks[PIDTYPE_MAX];
62 struct rcu_head rcu;
63 int level;
64 struct upid numbers[1];
65};
66
67extern struct pid init_struct_pid;
68
69struct 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
82extern void FASTCALL(put_pid(struct pid *pid));
83extern struct task_struct *FASTCALL(pid_task(struct pid *pid, enum pid_type));
84extern struct task_struct *FASTCALL(get_pid_task(struct pid *pid,
85 enum pid_type));
86
87extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
88
89/*
90 * attach_pid() and detach_pid() must be called with the tasklist_lock
91 * write-held.
92 */
93extern int FASTCALL(attach_pid(struct task_struct *task,
94 enum pid_type type, struct pid *pid));
95extern void FASTCALL(detach_pid(struct task_struct *task, enum pid_type));
96extern void FASTCALL(transfer_pid(struct task_struct *old,
97 struct task_struct *new, enum pid_type));
98
99struct pid_namespace;
100extern struct pid_namespace init_pid_ns;
101
102/*
103 * look up a PID in the hash table. Must be called with the tasklist_lock
104 * or rcu_read_lock() held.
105 *
106 * find_pid_ns() finds the pid in the namespace specified
107 * find_pid() find the pid by its global id, i.e. in the init namespace
108 * find_vpid() finr the pid by its virtual id, i.e. in the current namespace
109 *
110 * see also find_task_by_pid() set in include/linux/sched.h
111 */
112extern struct pid *FASTCALL(find_pid_ns(int nr, struct pid_namespace *ns));
113extern struct pid *find_vpid(int nr);
114extern struct pid *find_pid(int nr);
115
116/*
117 * Lookup a PID in the hash table, and return with it's count elevated.
118 */
119extern struct pid *find_get_pid(int nr);
120extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
121
122extern struct pid *alloc_pid(struct pid_namespace *ns);
123extern void FASTCALL(free_pid(struct pid *pid));
124extern void zap_pid_ns_processes(struct pid_namespace *pid_ns);
125
126/*
127 * the helpers to get the pid's id seen from different namespaces
128 *
129 * pid_nr() : global id, i.e. the id seen from the init namespace;
130 * pid_vnr() : virtual id, i.e. the id seen from the namespace this pid
131 * belongs to. this only makes sence when called in the
132 * context of the task that belongs to the same namespace;
133 * pid_nr_ns() : id seen from the ns specified.
134 *
135 * see also task_xid_nr() etc in include/linux/sched.h
136 */
137
138static inline pid_t pid_nr(struct pid *pid)
139{
140 pid_t nr = 0;
141 if (pid)
142 nr = pid->numbers[0].nr;
143 return nr;
144}
145
146pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
147
148static inline pid_t pid_vnr(struct pid *pid)
149{
150 pid_t nr = 0;
151 if (pid)
152 nr = pid->numbers[pid->level].nr;
153 return nr;
154}
155
156#define do_each_pid_task(pid, type, task) \
157 do { \
158 struct hlist_node *pos___; \
159 if (pid != NULL) \
160 hlist_for_each_entry_rcu((task), pos___, \
161 &pid->tasks[type], pids[type].node) {
162
163#define while_each_pid_task(pid, type, task) \
164 } \
165 } while (0)
166
167#endif /* _LINUX_PID_H */