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#include <linux/wait.h>
7#include <linux/refcount.h>
8
9enum pid_type
10{
11 PIDTYPE_PID,
12 PIDTYPE_TGID,
13 PIDTYPE_PGID,
14 PIDTYPE_SID,
15 PIDTYPE_MAX,
16};
17
18/*
19 * What is struct pid?
20 *
21 * A struct pid is the kernel's internal notion of a process identifier.
22 * It refers to individual tasks, process groups, and sessions. While
23 * there are processes attached to it the struct pid lives in a hash
24 * table, so it and then the processes that it refers to can be found
25 * quickly from the numeric pid value. The attached processes may be
26 * quickly accessed by following pointers from struct pid.
27 *
28 * Storing pid_t values in the kernel and referring to them later has a
29 * problem. The process originally with that pid may have exited and the
30 * pid allocator wrapped, and another process could have come along
31 * and been assigned that pid.
32 *
33 * Referring to user space processes by holding a reference to struct
34 * task_struct has a problem. When the user space process exits
35 * the now useless task_struct is still kept. A task_struct plus a
36 * stack consumes around 10K of low kernel memory. More precisely
37 * this is THREAD_SIZE + sizeof(struct task_struct). By comparison
38 * a struct pid is about 64 bytes.
39 *
40 * Holding a reference to struct pid solves both of these problems.
41 * It is small so holding a reference does not consume a lot of
42 * resources, and since a new struct pid is allocated when the numeric pid
43 * value is reused (when pids wrap around) we don't mistakenly refer to new
44 * processes.
45 */
46
47
48/*
49 * struct upid is used to get the id of the struct pid, as it is
50 * seen in particular namespace. Later the struct pid is found with
51 * find_pid_ns() using the int nr and struct pid_namespace *ns.
52 */
53
54struct upid {
55 int nr;
56 struct pid_namespace *ns;
57};
58
59struct pid
60{
61 refcount_t count;
62 unsigned int level;
63 /* lists of tasks that use this pid */
64 struct hlist_head tasks[PIDTYPE_MAX];
65 /* wait queue for pidfd notifications */
66 wait_queue_head_t wait_pidfd;
67 struct rcu_head rcu;
68 struct upid numbers[1];
69};
70
71extern struct pid init_struct_pid;
72
73extern const struct file_operations pidfd_fops;
74
75struct file;
76
77extern struct pid *pidfd_pid(const struct file *file);
78
79static inline struct pid *get_pid(struct pid *pid)
80{
81 if (pid)
82 refcount_inc(&pid->count);
83 return pid;
84}
85
86extern void put_pid(struct pid *pid);
87extern struct task_struct *pid_task(struct pid *pid, enum pid_type);
88static inline bool pid_has_task(struct pid *pid, enum pid_type type)
89{
90 return !hlist_empty(&pid->tasks[type]);
91}
92extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type);
93
94extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
95
96/*
97 * these helpers must be called with the tasklist_lock write-held.
98 */
99extern void attach_pid(struct task_struct *task, enum pid_type);
100extern void detach_pid(struct task_struct *task, enum pid_type);
101extern void change_pid(struct task_struct *task, enum pid_type,
102 struct pid *pid);
103extern void transfer_pid(struct task_struct *old, struct task_struct *new,
104 enum pid_type);
105
106struct pid_namespace;
107extern struct pid_namespace init_pid_ns;
108
109/*
110 * look up a PID in the hash table. Must be called with the tasklist_lock
111 * or rcu_read_lock() held.
112 *
113 * find_pid_ns() finds the pid in the namespace specified
114 * find_vpid() finds the pid by its virtual id, i.e. in the current namespace
115 *
116 * see also find_task_by_vpid() set in include/linux/sched.h
117 */
118extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns);
119extern struct pid *find_vpid(int nr);
120
121/*
122 * Lookup a PID in the hash table, and return with it's count elevated.
123 */
124extern struct pid *find_get_pid(int nr);
125extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
126
127extern struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
128 size_t set_tid_size);
129extern void free_pid(struct pid *pid);
130extern void disable_pid_allocation(struct pid_namespace *ns);
131
132/*
133 * ns_of_pid() returns the pid namespace in which the specified pid was
134 * allocated.
135 *
136 * NOTE:
137 * ns_of_pid() is expected to be called for a process (task) that has
138 * an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid
139 * is expected to be non-NULL. If @pid is NULL, caller should handle
140 * the resulting NULL pid-ns.
141 */
142static inline struct pid_namespace *ns_of_pid(struct pid *pid)
143{
144 struct pid_namespace *ns = NULL;
145 if (pid)
146 ns = pid->numbers[pid->level].ns;
147 return ns;
148}
149
150/*
151 * is_child_reaper returns true if the pid is the init process
152 * of the current namespace. As this one could be checked before
153 * pid_ns->child_reaper is assigned in copy_process, we check
154 * with the pid number.
155 */
156static inline bool is_child_reaper(struct pid *pid)
157{
158 return pid->numbers[pid->level].nr == 1;
159}
160
161/*
162 * the helpers to get the pid's id seen from different namespaces
163 *
164 * pid_nr() : global id, i.e. the id seen from the init namespace;
165 * pid_vnr() : virtual id, i.e. the id seen from the pid namespace of
166 * current.
167 * pid_nr_ns() : id seen from the ns specified.
168 *
169 * see also task_xid_nr() etc in include/linux/sched.h
170 */
171
172static inline pid_t pid_nr(struct pid *pid)
173{
174 pid_t nr = 0;
175 if (pid)
176 nr = pid->numbers[0].nr;
177 return nr;
178}
179
180pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
181pid_t pid_vnr(struct pid *pid);
182
183#define do_each_pid_task(pid, type, task) \
184 do { \
185 if ((pid) != NULL) \
186 hlist_for_each_entry_rcu((task), \
187 &(pid)->tasks[type], pid_links[type]) {
188
189 /*
190 * Both old and new leaders may be attached to
191 * the same pid in the middle of de_thread().
192 */
193#define while_each_pid_task(pid, type, task) \
194 if (type == PIDTYPE_PID) \
195 break; \
196 } \
197 } while (0)
198
199#define do_each_pid_thread(pid, type, task) \
200 do_each_pid_task(pid, type, task) { \
201 struct task_struct *tg___ = task; \
202 for_each_thread(tg___, task) {
203
204#define while_each_pid_thread(pid, type, task) \
205 } \
206 task = tg___; \
207 } while_each_pid_task(pid, type, task)
208#endif /* _LINUX_PID_H */