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