Linux kernel mirror (for testing)
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linux
1#ifndef _LINUX_PID_H
2#define _LINUX_PID_H
3
4#include <linux/rculist.h>
5
6enum pid_type
7{
8 PIDTYPE_PID,
9 PIDTYPE_PGID,
10 PIDTYPE_SID,
11 PIDTYPE_MAX,
12 /* only valid to __task_pid_nr_ns() */
13 __PIDTYPE_TGID
14};
15
16/*
17 * What is struct pid?
18 *
19 * A struct pid is the kernel's internal notion of a process identifier.
20 * It refers to individual tasks, process groups, and sessions. While
21 * there are processes attached to it the struct pid lives in a hash
22 * table, so it and then the processes that it refers to can be found
23 * quickly from the numeric pid value. The attached processes may be
24 * quickly accessed by following pointers from struct pid.
25 *
26 * Storing pid_t values in the kernel and referring to them later has a
27 * problem. The process originally with that pid may have exited and the
28 * pid allocator wrapped, and another process could have come along
29 * and been assigned that pid.
30 *
31 * Referring to user space processes by holding a reference to struct
32 * task_struct has a problem. When the user space process exits
33 * the now useless task_struct is still kept. A task_struct plus a
34 * stack consumes around 10K of low kernel memory. More precisely
35 * this is THREAD_SIZE + sizeof(struct task_struct). By comparison
36 * a struct pid is about 64 bytes.
37 *
38 * Holding a reference to struct pid solves both of these problems.
39 * It is small so holding a reference does not consume a lot of
40 * resources, and since a new struct pid is allocated when the numeric pid
41 * value is reused (when pids wrap around) we don't mistakenly refer to new
42 * processes.
43 */
44
45
46/*
47 * struct upid is used to get the id of the struct pid, as it is
48 * seen in particular namespace. Later the struct pid is found with
49 * find_pid_ns() using the int nr and struct pid_namespace *ns.
50 */
51
52struct upid {
53 /* Try to keep pid_chain in the same cacheline as nr for find_vpid */
54 int nr;
55 struct pid_namespace *ns;
56 struct hlist_node pid_chain;
57};
58
59struct pid
60{
61 atomic_t count;
62 unsigned int level;
63 /* lists of tasks that use this pid */
64 struct hlist_head tasks[PIDTYPE_MAX];
65 struct rcu_head rcu;
66 struct upid numbers[1];
67};
68
69extern struct pid init_struct_pid;
70
71struct pid_link
72{
73 struct hlist_node node;
74 struct pid *pid;
75};
76
77static inline struct pid *get_pid(struct pid *pid)
78{
79 if (pid)
80 atomic_inc(&pid->count);
81 return pid;
82}
83
84extern void put_pid(struct pid *pid);
85extern struct task_struct *pid_task(struct pid *pid, enum pid_type);
86extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type);
87
88extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
89
90/*
91 * these helpers must be called with the tasklist_lock write-held.
92 */
93extern void attach_pid(struct task_struct *task, enum pid_type);
94extern void detach_pid(struct task_struct *task, enum pid_type);
95extern void change_pid(struct task_struct *task, enum pid_type,
96 struct pid *pid);
97extern void transfer_pid(struct task_struct *old, struct task_struct *new,
98 enum pid_type);
99
100struct pid_namespace;
101extern struct pid_namespace init_pid_ns;
102
103/*
104 * look up a PID in the hash table. Must be called with the tasklist_lock
105 * or rcu_read_lock() held.
106 *
107 * find_pid_ns() finds the pid in the namespace specified
108 * find_vpid() finds the pid by its virtual id, i.e. in the current namespace
109 *
110 * see also find_task_by_vpid() set in include/linux/sched.h
111 */
112extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns);
113extern struct pid *find_vpid(int nr);
114
115/*
116 * Lookup a PID in the hash table, and return with it's count elevated.
117 */
118extern struct pid *find_get_pid(int nr);
119extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
120int next_pidmap(struct pid_namespace *pid_ns, unsigned int last);
121
122extern struct pid *alloc_pid(struct pid_namespace *ns);
123extern void free_pid(struct pid *pid);
124extern void disable_pid_allocation(struct pid_namespace *ns);
125
126/*
127 * ns_of_pid() returns the pid namespace in which the specified pid was
128 * allocated.
129 *
130 * NOTE:
131 * ns_of_pid() is expected to be called for a process (task) that has
132 * an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid
133 * is expected to be non-NULL. If @pid is NULL, caller should handle
134 * the resulting NULL pid-ns.
135 */
136static inline struct pid_namespace *ns_of_pid(struct pid *pid)
137{
138 struct pid_namespace *ns = NULL;
139 if (pid)
140 ns = pid->numbers[pid->level].ns;
141 return ns;
142}
143
144/*
145 * is_child_reaper returns true if the pid is the init process
146 * of the current namespace. As this one could be checked before
147 * pid_ns->child_reaper is assigned in copy_process, we check
148 * with the pid number.
149 */
150static inline bool is_child_reaper(struct pid *pid)
151{
152 return pid->numbers[pid->level].nr == 1;
153}
154
155/*
156 * the helpers to get the pid's id seen from different namespaces
157 *
158 * pid_nr() : global id, i.e. the id seen from the init namespace;
159 * pid_vnr() : virtual id, i.e. the id seen from the pid namespace of
160 * current.
161 * pid_nr_ns() : id seen from the ns specified.
162 *
163 * see also task_xid_nr() etc in include/linux/sched.h
164 */
165
166static inline pid_t pid_nr(struct pid *pid)
167{
168 pid_t nr = 0;
169 if (pid)
170 nr = pid->numbers[0].nr;
171 return nr;
172}
173
174pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
175pid_t pid_vnr(struct pid *pid);
176
177#define do_each_pid_task(pid, type, task) \
178 do { \
179 if ((pid) != NULL) \
180 hlist_for_each_entry_rcu((task), \
181 &(pid)->tasks[type], pids[type].node) {
182
183 /*
184 * Both old and new leaders may be attached to
185 * the same pid in the middle of de_thread().
186 */
187#define while_each_pid_task(pid, type, task) \
188 if (type == PIDTYPE_PID) \
189 break; \
190 } \
191 } while (0)
192
193#define do_each_pid_thread(pid, type, task) \
194 do_each_pid_task(pid, type, task) { \
195 struct task_struct *tg___ = task; \
196 for_each_thread(tg___, task) {
197
198#define while_each_pid_thread(pid, type, task) \
199 } \
200 task = tg___; \
201 } while_each_pid_task(pid, type, task)
202#endif /* _LINUX_PID_H */