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 spinlock_t lock;
64 /* lists of tasks that use this pid */
65 struct hlist_head tasks[PIDTYPE_MAX];
66 struct hlist_head inodes;
67 /* wait queue for pidfd notifications */
68 wait_queue_head_t wait_pidfd;
69 struct rcu_head rcu;
70 struct upid numbers[1];
71};
72
73extern struct pid init_struct_pid;
74
75extern const struct file_operations pidfd_fops;
76
77struct file;
78
79extern struct pid *pidfd_pid(const struct file *file);
80struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags);
81struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags);
82int pidfd_create(struct pid *pid, unsigned int flags);
83
84static inline struct pid *get_pid(struct pid *pid)
85{
86 if (pid)
87 refcount_inc(&pid->count);
88 return pid;
89}
90
91extern void put_pid(struct pid *pid);
92extern struct task_struct *pid_task(struct pid *pid, enum pid_type);
93static inline bool pid_has_task(struct pid *pid, enum pid_type type)
94{
95 return !hlist_empty(&pid->tasks[type]);
96}
97extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type);
98
99extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
100
101/*
102 * these helpers must be called with the tasklist_lock write-held.
103 */
104extern void attach_pid(struct task_struct *task, enum pid_type);
105extern void detach_pid(struct task_struct *task, enum pid_type);
106extern void change_pid(struct task_struct *task, enum pid_type,
107 struct pid *pid);
108extern void exchange_tids(struct task_struct *task, struct task_struct *old);
109extern void transfer_pid(struct task_struct *old, struct task_struct *new,
110 enum pid_type);
111
112struct pid_namespace;
113extern struct pid_namespace init_pid_ns;
114
115extern int pid_max;
116extern int pid_max_min, pid_max_max;
117
118/*
119 * look up a PID in the hash table. Must be called with the tasklist_lock
120 * or rcu_read_lock() held.
121 *
122 * find_pid_ns() finds the pid in the namespace specified
123 * find_vpid() finds the pid by its virtual id, i.e. in the current namespace
124 *
125 * see also find_task_by_vpid() set in include/linux/sched.h
126 */
127extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns);
128extern struct pid *find_vpid(int nr);
129
130/*
131 * Lookup a PID in the hash table, and return with it's count elevated.
132 */
133extern struct pid *find_get_pid(int nr);
134extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
135
136extern struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
137 size_t set_tid_size);
138extern void free_pid(struct pid *pid);
139extern void disable_pid_allocation(struct pid_namespace *ns);
140
141/*
142 * ns_of_pid() returns the pid namespace in which the specified pid was
143 * allocated.
144 *
145 * NOTE:
146 * ns_of_pid() is expected to be called for a process (task) that has
147 * an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid
148 * is expected to be non-NULL. If @pid is NULL, caller should handle
149 * the resulting NULL pid-ns.
150 */
151static inline struct pid_namespace *ns_of_pid(struct pid *pid)
152{
153 struct pid_namespace *ns = NULL;
154 if (pid)
155 ns = pid->numbers[pid->level].ns;
156 return ns;
157}
158
159/*
160 * is_child_reaper returns true if the pid is the init process
161 * of the current namespace. As this one could be checked before
162 * pid_ns->child_reaper is assigned in copy_process, we check
163 * with the pid number.
164 */
165static inline bool is_child_reaper(struct pid *pid)
166{
167 return pid->numbers[pid->level].nr == 1;
168}
169
170/*
171 * the helpers to get the pid's id seen from different namespaces
172 *
173 * pid_nr() : global id, i.e. the id seen from the init namespace;
174 * pid_vnr() : virtual id, i.e. the id seen from the pid namespace of
175 * current.
176 * pid_nr_ns() : id seen from the ns specified.
177 *
178 * see also task_xid_nr() etc in include/linux/sched.h
179 */
180
181static inline pid_t pid_nr(struct pid *pid)
182{
183 pid_t nr = 0;
184 if (pid)
185 nr = pid->numbers[0].nr;
186 return nr;
187}
188
189pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
190pid_t pid_vnr(struct pid *pid);
191
192#define do_each_pid_task(pid, type, task) \
193 do { \
194 if ((pid) != NULL) \
195 hlist_for_each_entry_rcu((task), \
196 &(pid)->tasks[type], pid_links[type]) {
197
198 /*
199 * Both old and new leaders may be attached to
200 * the same pid in the middle of de_thread().
201 */
202#define while_each_pid_task(pid, type, task) \
203 if (type == PIDTYPE_PID) \
204 break; \
205 } \
206 } while (0)
207
208#define do_each_pid_thread(pid, type, task) \
209 do_each_pid_task(pid, type, task) { \
210 struct task_struct *tg___ = task; \
211 for_each_thread(tg___, task) {
212
213#define while_each_pid_thread(pid, type, task) \
214 } \
215 task = tg___; \
216 } while_each_pid_task(pid, type, task)
217#endif /* _LINUX_PID_H */
218

source code of linux/include/linux/pid.h