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