Commit | Line | Data |
---|---|---|
1da177e4 LT |
1 | #ifndef _LINUX_PID_H |
2 | #define _LINUX_PID_H | |
3 | ||
92476d7f EB |
4 | #include <linux/rcupdate.h> |
5 | ||
1da177e4 LT |
6 | enum pid_type |
7 | { | |
8 | PIDTYPE_PID, | |
1da177e4 LT |
9 | PIDTYPE_PGID, |
10 | PIDTYPE_SID, | |
11 | PIDTYPE_MAX | |
12 | }; | |
13 | ||
92476d7f EB |
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 | |
84d73786 SB |
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. | |
92476d7f EB |
41 | */ |
42 | ||
4c3f2ead SB |
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 | ||
50 | struct 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 | ||
1da177e4 LT |
57 | struct pid |
58 | { | |
92476d7f | 59 | atomic_t count; |
92476d7f EB |
60 | /* lists of tasks that use this pid */ |
61 | struct hlist_head tasks[PIDTYPE_MAX]; | |
62 | struct rcu_head rcu; | |
caafa432 | 63 | unsigned int level; |
4c3f2ead | 64 | struct upid numbers[1]; |
1da177e4 LT |
65 | }; |
66 | ||
820e45db SB |
67 | extern struct pid init_struct_pid; |
68 | ||
92476d7f EB |
69 | struct pid_link |
70 | { | |
71 | struct hlist_node node; | |
72 | struct pid *pid; | |
73 | }; | |
74 | ||
75 | static inline struct pid *get_pid(struct pid *pid) | |
76 | { | |
77 | if (pid) | |
78 | atomic_inc(&pid->count); | |
79 | return pid; | |
80 | } | |
81 | ||
b3c97528 HH |
82 | extern void put_pid(struct pid *pid); |
83 | extern struct task_struct *pid_task(struct pid *pid, enum pid_type); | |
84 | extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type); | |
1da177e4 | 85 | |
1a657f78 ON |
86 | extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type); |
87 | ||
1da177e4 LT |
88 | /* |
89 | * attach_pid() and detach_pid() must be called with the tasklist_lock | |
90 | * write-held. | |
91 | */ | |
24336eae ON |
92 | extern void attach_pid(struct task_struct *task, enum pid_type type, |
93 | struct pid *pid); | |
b3c97528 | 94 | extern void detach_pid(struct task_struct *task, enum pid_type); |
24336eae ON |
95 | extern void change_pid(struct task_struct *task, enum pid_type, |
96 | struct pid *pid); | |
b3c97528 HH |
97 | extern void transfer_pid(struct task_struct *old, struct task_struct *new, |
98 | enum pid_type); | |
1da177e4 | 99 | |
198fe21b PE |
100 | struct pid_namespace; |
101 | extern struct pid_namespace init_pid_ns; | |
102 | ||
1da177e4 LT |
103 | /* |
104 | * look up a PID in the hash table. Must be called with the tasklist_lock | |
92476d7f | 105 | * or rcu_read_lock() held. |
198fe21b PE |
106 | * |
107 | * find_pid_ns() finds the pid in the namespace specified | |
108 | * find_pid() find the pid by its global id, i.e. in the init namespace | |
109 | * find_vpid() finr the pid by its virtual id, i.e. in the current namespace | |
110 | * | |
111 | * see also find_task_by_pid() set in include/linux/sched.h | |
92476d7f | 112 | */ |
b3c97528 | 113 | extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns); |
8990571e PE |
114 | extern struct pid *find_vpid(int nr); |
115 | extern struct pid *find_pid(int nr); | |
92476d7f EB |
116 | |
117 | /* | |
118 | * Lookup a PID in the hash table, and return with it's count elevated. | |
1da177e4 | 119 | */ |
92476d7f | 120 | extern struct pid *find_get_pid(int nr); |
198fe21b | 121 | extern struct pid *find_ge_pid(int nr, struct pid_namespace *); |
74bd59bb | 122 | int next_pidmap(struct pid_namespace *pid_ns, int last); |
1da177e4 | 123 | |
8ef047aa | 124 | extern struct pid *alloc_pid(struct pid_namespace *ns); |
b3c97528 | 125 | extern void free_pid(struct pid *pid); |
1da177e4 | 126 | |
7af57294 PE |
127 | /* |
128 | * the helpers to get the pid's id seen from different namespaces | |
129 | * | |
130 | * pid_nr() : global id, i.e. the id seen from the init namespace; | |
44c4e1b2 EB |
131 | * pid_vnr() : virtual id, i.e. the id seen from the pid namespace of |
132 | * current. | |
7af57294 PE |
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 | ||
5feb8f5f EB |
138 | static inline pid_t pid_nr(struct pid *pid) |
139 | { | |
140 | pid_t nr = 0; | |
141 | if (pid) | |
7af57294 PE |
142 | nr = pid->numbers[0].nr; |
143 | return nr; | |
144 | } | |
145 | ||
146 | pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns); | |
44c4e1b2 | 147 | pid_t pid_vnr(struct pid *pid); |
5feb8f5f | 148 | |
1d32849b AM |
149 | #define do_each_pid_task(pid, type, task) \ |
150 | do { \ | |
151 | struct hlist_node *pos___; \ | |
152 | if (pid != NULL) \ | |
153 | hlist_for_each_entry_rcu((task), pos___, \ | |
d387cae0 ON |
154 | &pid->tasks[type], pids[type].node) { |
155 | ||
46f382d2 ON |
156 | /* |
157 | * Both old and new leaders may be attached to | |
158 | * the same pid in the middle of de_thread(). | |
159 | */ | |
1d32849b | 160 | #define while_each_pid_task(pid, type, task) \ |
46f382d2 ON |
161 | if (type == PIDTYPE_PID) \ |
162 | break; \ | |
1d32849b | 163 | } \ |
d387cae0 | 164 | } while (0) |
558cb325 | 165 | |
1da177e4 | 166 | #endif /* _LINUX_PID_H */ |