1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef _LINUX_PID_H
3#define _LINUX_PID_H
4
5#include <linux/rculist.h>
6
7enum pid_type
8{
9 PIDTYPE_PID,
10 PIDTYPE_TGID,
11 PIDTYPE_PGID,
12 PIDTYPE_SID,
13 PIDTYPE_MAX,
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 int nr;
54 struct pid_namespace *ns;
55};
56
57struct pid
58{
59 atomic_t count;
60 unsigned int level;
61 /* lists of tasks that use this pid */
62 struct hlist_head tasks[PIDTYPE_MAX];
63 struct rcu_head rcu;
64 struct upid numbers[1];
65};
66
67extern struct pid init_struct_pid;
68
69static inline struct pid *get_pid(struct pid *pid)
70{
71 if (pid)
72 atomic_inc(&pid->count);
73 return pid;
74}
75
76extern void put_pid(struct pid *pid);
77extern struct task_struct *pid_task(struct pid *pid, enum pid_type);
78extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type);
79
80extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
81
82/*
83 * these helpers must be called with the tasklist_lock write-held.
84 */
85extern void attach_pid(struct task_struct *task, enum pid_type);
86extern void detach_pid(struct task_struct *task, enum pid_type);
87extern void change_pid(struct task_struct *task, enum pid_type,
88 struct pid *pid);
89extern void transfer_pid(struct task_struct *old, struct task_struct *new,
90 enum pid_type);
91
92struct pid_namespace;
93extern struct pid_namespace init_pid_ns;
94
95/*
96 * look up a PID in the hash table. Must be called with the tasklist_lock
97 * or rcu_read_lock() held.
98 *
99 * find_pid_ns() finds the pid in the namespace specified
100 * find_vpid() finds the pid by its virtual id, i.e. in the current namespace
101 *
102 * see also find_task_by_vpid() set in include/linux/sched.h
103 */
104extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns);
105extern struct pid *find_vpid(int nr);
106
107/*
108 * Lookup a PID in the hash table, and return with it's count elevated.
109 */
110extern struct pid *find_get_pid(int nr);
111extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
112
113extern struct pid *alloc_pid(struct pid_namespace *ns);
114extern void free_pid(struct pid *pid);
115extern void disable_pid_allocation(struct pid_namespace *ns);
116
117/*
118 * ns_of_pid() returns the pid namespace in which the specified pid was
119 * allocated.
120 *
121 * NOTE:
122 * ns_of_pid() is expected to be called for a process (task) that has
123 * an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid
124 * is expected to be non-NULL. If @pid is NULL, caller should handle
125 * the resulting NULL pid-ns.
126 */
127static inline struct pid_namespace *ns_of_pid(struct pid *pid)
128{
129 struct pid_namespace *ns = NULL;
130 if (pid)
131 ns = pid->numbers[pid->level].ns;
132 return ns;
133}
134
135/*
136 * is_child_reaper returns true if the pid is the init process
137 * of the current namespace. As this one could be checked before
138 * pid_ns->child_reaper is assigned in copy_process, we check
139 * with the pid number.
140 */
141static inline bool is_child_reaper(struct pid *pid)
142{
143 return pid->numbers[pid->level].nr == 1;
144}
145
146/*
147 * the helpers to get the pid's id seen from different namespaces
148 *
149 * pid_nr() : global id, i.e. the id seen from the init namespace;
150 * pid_vnr() : virtual id, i.e. the id seen from the pid namespace of
151 * current.
152 * pid_nr_ns() : id seen from the ns specified.
153 *
154 * see also task_xid_nr() etc in include/linux/sched.h
155 */
156
157static inline pid_t pid_nr(struct pid *pid)
158{
159 pid_t nr = 0;
160 if (pid)
161 nr = pid->numbers[0].nr;
162 return nr;
163}
164
165pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
166pid_t pid_vnr(struct pid *pid);
167
168#define do_each_pid_task(pid, type, task) \
169 do { \
170 if ((pid) != NULL) \
171 hlist_for_each_entry_rcu((task), \
172 &(pid)->tasks[type], pid_links[type]) {
173
174 /*
175 * Both old and new leaders may be attached to
176 * the same pid in the middle of de_thread().
177 */
178#define while_each_pid_task(pid, type, task) \
179 if (type == PIDTYPE_PID) \
180 break; \
181 } \
182 } while (0)
183
184#define do_each_pid_thread(pid, type, task) \
185 do_each_pid_task(pid, type, task) { \
186 struct task_struct *tg___ = task; \
187 for_each_thread(tg___, task) {
188
189#define while_each_pid_thread(pid, type, task) \
190 } \
191 task = tg___; \
192 } while_each_pid_task(pid, type, task)
193#endif /* _LINUX_PID_H */
194