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