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