1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef _LINUX_PID_H
3 #define _LINUX_PID_H
4
5 #include <linux/pid_types.h>
6 #include <linux/rculist.h>
7 #include <linux/rcupdate.h>
8 #include <linux/refcount.h>
9 #include <linux/sched.h>
10 #include <linux/wait.h>
11
12 /*
13 * What is struct pid?
14 *
15 * A struct pid is the kernel's internal notion of a process identifier.
16 * It refers to individual tasks, process groups, and sessions. While
17 * there are processes attached to it the struct pid lives in a hash
18 * table, so it and then the processes that it refers to can be found
19 * quickly from the numeric pid value. The attached processes may be
20 * quickly accessed by following pointers from struct pid.
21 *
22 * Storing pid_t values in the kernel and referring to them later has a
23 * problem. The process originally with that pid may have exited and the
24 * pid allocator wrapped, and another process could have come along
25 * and been assigned that pid.
26 *
27 * Referring to user space processes by holding a reference to struct
28 * task_struct has a problem. When the user space process exits
29 * the now useless task_struct is still kept. A task_struct plus a
30 * stack consumes around 10K of low kernel memory. More precisely
31 * this is THREAD_SIZE + sizeof(struct task_struct). By comparison
32 * a struct pid is about 64 bytes.
33 *
34 * Holding a reference to struct pid solves both of these problems.
35 * It is small so holding a reference does not consume a lot of
36 * resources, and since a new struct pid is allocated when the numeric pid
37 * value is reused (when pids wrap around) we don't mistakenly refer to new
38 * processes.
39 */
40
41
42 /*
43 * struct upid is used to get the id of the struct pid, as it is
44 * seen in particular namespace. Later the struct pid is found with
45 * find_pid_ns() using the int nr and struct pid_namespace *ns.
46 */
47
48 #define RESERVED_PIDS 300
49
50 struct upid {
51 int nr;
52 struct pid_namespace *ns;
53 };
54
55 struct pid
56 {
57 refcount_t count;
58 unsigned int level;
59 spinlock_t lock;
60 struct dentry *stashed;
61 u64 ino;
62 /* lists of tasks that use this pid */
63 struct hlist_head tasks[PIDTYPE_MAX];
64 struct hlist_head inodes;
65 /* wait queue for pidfd notifications */
66 wait_queue_head_t wait_pidfd;
67 struct rcu_head rcu;
68 struct upid numbers[];
69 };
70
71 extern struct pid init_struct_pid;
72
73 struct file;
74
75 struct pid *pidfd_pid(const struct file *file);
76 struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags);
77 struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags);
78 int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret);
79 void do_notify_pidfd(struct task_struct *task);
80
81 static inline struct pid *get_pid(struct pid *pid)
82 {
83 if (pid)
84 refcount_inc(&pid->count);
85 return pid;
86 }
87
88 extern void put_pid(struct pid *pid);
89 extern struct task_struct *pid_task(struct pid *pid, enum pid_type);
90 static inline bool pid_has_task(struct pid *pid, enum pid_type type)
91 {
92 return !hlist_empty(&pid->tasks[type]);
93 }
94 extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type);
95
96 extern 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 */
101 extern void attach_pid(struct task_struct *task, enum pid_type);
102 extern void detach_pid(struct task_struct *task, enum pid_type);
103 extern void change_pid(struct task_struct *task, enum pid_type,
104 struct pid *pid);
105 extern void exchange_tids(struct task_struct *task, struct task_struct *old);
106 extern void transfer_pid(struct task_struct *old, struct task_struct *new,
107 enum pid_type);
108
109 extern int pid_max;
110 extern int pid_max_min, pid_max_max;
111
112 /*
113 * look up a PID in the hash table. Must be called with the tasklist_lock
114 * or rcu_read_lock() held.
115 *
116 * find_pid_ns() finds the pid in the namespace specified
117 * find_vpid() finds the pid by its virtual id, i.e. in the current namespace
118 *
119 * see also find_task_by_vpid() set in include/linux/sched.h
120 */
121 extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns);
122 extern struct pid *find_vpid(int nr);
123
124 /*
125 * Lookup a PID in the hash table, and return with it's count elevated.
126 */
127 extern struct pid *find_get_pid(int nr);
128 extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
129
130 extern struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
131 size_t set_tid_size);
132 extern void free_pid(struct pid *pid);
133 extern void disable_pid_allocation(struct pid_namespace *ns);
134
135 /*
136 * ns_of_pid() returns the pid namespace in which the specified pid was
137 * allocated.
138 *
139 * NOTE:
140 * ns_of_pid() is expected to be called for a process (task) that has
141 * an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid
142 * is expected to be non-NULL. If @pid is NULL, caller should handle
143 * the resulting NULL pid-ns.
144 */
145 static inline struct pid_namespace *ns_of_pid(struct pid *pid)
146 {
147 struct pid_namespace *ns = NULL;
148 if (pid)
149 ns = pid->numbers[pid->level].ns;
150 return ns;
151 }
152
153 /*
154 * is_child_reaper returns true if the pid is the init process
155 * of the current namespace. As this one could be checked before
156 * pid_ns->child_reaper is assigned in copy_process, we check
157 * with the pid number.
158 */
159 static inline bool is_child_reaper(struct pid *pid)
160 {
161 return pid->numbers[pid->level].nr == 1;
162 }
163
164 /*
165 * the helpers to get the pid's id seen from different namespaces
166 *
167 * pid_nr() : global id, i.e. the id seen from the init namespace;
168 * pid_vnr() : virtual id, i.e. the id seen from the pid namespace of
169 * current.
170 * pid_nr_ns() : id seen from the ns specified.
171 *
172 * see also task_xid_nr() etc in include/linux/sched.h
173 */
174
175 static inline pid_t pid_nr(struct pid *pid)
176 {
177 pid_t nr = 0;
178 if (pid)
179 nr = pid->numbers[0].nr;
180 return nr;
181 }
182
183 pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
184 pid_t pid_vnr(struct pid *pid);
185
186 #define do_each_pid_task(pid, type, task) \
187 do { \
188 if ((pid) != NULL) \
189 hlist_for_each_entry_rcu((task), \
190 &(pid)->tasks[type], pid_links[type]) {
191
192 /*
193 * Both old and new leaders may be attached to
194 * the same pid in the middle of de_thread().
195 */
196 #define while_each_pid_task(pid, type, task) \
197 if (type == PIDTYPE_PID) \
198 break; \
199 } \
200 } while (0)
201
202 #define do_each_pid_thread(pid, type, task) \
203 do_each_pid_task(pid, type, task) { \
204 struct task_struct *tg___ = task; \
205 for_each_thread(tg___, task) {
206
207 #define while_each_pid_thread(pid, type, task) \
208 } \
209 task = tg___; \
210 } while_each_pid_task(pid, type, task)
211
212 static inline struct pid *task_pid(struct task_struct *task)
213 {
214 return task->thread_pid;
215 }
216
217 /*
218 * the helpers to get the task's different pids as they are seen
219 * from various namespaces
220 *
221 * task_xid_nr() : global id, i.e. the id seen from the init namespace;
222 * task_xid_vnr() : virtual id, i.e. the id seen from the pid namespace of
223 * current.
224 * task_xid_nr_ns() : id seen from the ns specified;
225 *
226 * see also pid_nr() etc in include/linux/pid.h
227 */
228 pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type, struct pid_namespace *ns);
229
230 static inline pid_t task_pid_nr(struct task_struct *tsk)
231 {
232 return tsk->pid;
233 }
234
235 static inline pid_t task_pid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
236 {
237 return __task_pid_nr_ns(tsk, PIDTYPE_PID, ns);
238 }
239
240 static inline pid_t task_pid_vnr(struct task_struct *tsk)
241 {
242 return __task_pid_nr_ns(tsk, PIDTYPE_PID, NULL);
243 }
244
245
246 static inline pid_t task_tgid_nr(struct task_struct *tsk)
247 {
248 return tsk->tgid;
249 }
250
251 /**
252 * pid_alive - check that a task structure is not stale
253 * @p: Task structure to be checked.
254 *
255 * Test if a process is not yet dead (at most zombie state)
256 * If pid_alive fails, then pointers within the task structure
257 * can be stale and must not be dereferenced.
258 *
259 * Return: 1 if the process is alive. 0 otherwise.
260 */
261 static inline int pid_alive(const struct task_struct *p)
262 {
263 return p->thread_pid != NULL;
264 }
265
266 static inline pid_t task_pgrp_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
267 {
268 return __task_pid_nr_ns(tsk, PIDTYPE_PGID, ns);
269 }
270
271 static inline pid_t task_pgrp_vnr(struct task_struct *tsk)
272 {
273 return __task_pid_nr_ns(tsk, PIDTYPE_PGID, NULL);
274 }
275
276
277 static inline pid_t task_session_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
278 {
279 return __task_pid_nr_ns(tsk, PIDTYPE_SID, ns);
280 }
281
282 static inline pid_t task_session_vnr(struct task_struct *tsk)
283 {
284 return __task_pid_nr_ns(tsk, PIDTYPE_SID, NULL);
285 }
286
287 static inline pid_t task_tgid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
288 {
289 return __task_pid_nr_ns(tsk, PIDTYPE_TGID, ns);
290 }
291
292 static inline pid_t task_tgid_vnr(struct task_struct *tsk)
293 {
294 return __task_pid_nr_ns(tsk, PIDTYPE_TGID, NULL);
295 }
296
297 static inline pid_t task_ppid_nr_ns(const struct task_struct *tsk, struct pid_namespace *ns)
298 {
299 pid_t pid = 0;
300
301 rcu_read_lock();
302 if (pid_alive(tsk))
303 pid = task_tgid_nr_ns(rcu_dereference(tsk->real_parent), ns);
304 rcu_read_unlock();
305
306 return pid;
307 }
308
309 static inline pid_t task_ppid_nr(const struct task_struct *tsk)
310 {
311 return task_ppid_nr_ns(tsk, &init_pid_ns);
312 }
313
314 /* Obsolete, do not use: */
315 static inline pid_t task_pgrp_nr(struct task_struct *tsk)
316 {
317 return task_pgrp_nr_ns(tsk, &init_pid_ns);
318 }
319
320 /**
321 * is_global_init - check if a task structure is init. Since init
322 * is free to have sub-threads we need to check tgid.
323 * @tsk: Task structure to be checked.
324 *
325 * Check if a task structure is the first user space task the kernel created.
326 *
327 * Return: 1 if the task structure is init. 0 otherwise.
328 */
329 static inline int is_global_init(struct task_struct *tsk)
330 {
331 return task_tgid_nr(tsk) == 1;
332 }
333
334 #endif /* _LINUX_PID_H */
335
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