pid.h

  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
 50struct pidfs_attr;
 51
 52struct upid {
 53	int nr;
 54	struct pid_namespace *ns;
 55};
 56
 57struct pid {
 58	refcount_t count;
 59	unsigned int level;
 60	spinlock_t lock;
 61	struct {
 62		u64 ino;
 63		struct rb_node pidfs_node;
 64		struct dentry *stashed;
 65		struct pidfs_attr *attr;
 66	};
 67	/* lists of tasks that use this pid */
 68	struct hlist_head tasks[PIDTYPE_MAX];
 69	struct hlist_head inodes;
 70	/* wait queue for pidfd notifications */
 71	wait_queue_head_t wait_pidfd;
 72	struct rcu_head rcu;
 73	struct upid numbers[];
 74};
 75
 76extern seqcount_spinlock_t pidmap_lock_seq;
 77extern struct pid init_struct_pid;
 78
 79struct file;
 80
 81struct pid *pidfd_pid(const struct file *file);
 82struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags);
 83struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags);
 84int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret_file);
 85void do_notify_pidfd(struct task_struct *task);
 86
 87static inline struct pid *get_pid(struct pid *pid)
 88{
 89	if (pid)
 90		refcount_inc(&pid->count);
 91	return pid;
 92}
 93
 94extern void put_pid(struct pid *pid);
 95extern struct task_struct *pid_task(struct pid *pid, enum pid_type);
 96static inline bool pid_has_task(struct pid *pid, enum pid_type type)
 97{
 98	return !hlist_empty(&pid->tasks[type]);
 99}
100extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type);
101
102extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
103
104/*
105 * these helpers must be called with the tasklist_lock write-held.
106 */
107extern void attach_pid(struct task_struct *task, enum pid_type);
108void detach_pid(struct pid **pids, struct task_struct *task, enum pid_type);
109void change_pid(struct pid **pids, struct task_struct *task, enum pid_type,
110		struct pid *pid);
111extern void exchange_tids(struct task_struct *task, struct task_struct *old);
112extern void transfer_pid(struct task_struct *old, struct task_struct *new,
113			 enum pid_type);
114
115/*
116 * look up a PID in the hash table. Must be called with the tasklist_lock
117 * or rcu_read_lock() held.
118 *
119 * find_pid_ns() finds the pid in the namespace specified
120 * find_vpid() finds the pid by its virtual id, i.e. in the current namespace
121 *
122 * see also find_task_by_vpid() set in include/linux/sched.h
123 */
124extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns);
125extern struct pid *find_vpid(int nr);
126
127/*
128 * Lookup a PID in the hash table, and return with it's count elevated.
129 */
130extern struct pid *find_get_pid(int nr);
131extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
132
133extern struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
134			     size_t set_tid_size);
135extern void free_pid(struct pid *pid);
136void free_pids(struct pid **pids);
137extern void disable_pid_allocation(struct pid_namespace *ns);
138
139/*
140 * ns_of_pid() returns the pid namespace in which the specified pid was
141 * allocated.
142 *
143 * NOTE:
144 * 	ns_of_pid() is expected to be called for a process (task) that has
145 * 	an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid
146 * 	is expected to be non-NULL. If @pid is NULL, caller should handle
147 * 	the resulting NULL pid-ns.
148 */
149static inline struct pid_namespace *ns_of_pid(struct pid *pid)
150{
151	struct pid_namespace *ns = NULL;
152	if (pid)
153		ns = pid->numbers[pid->level].ns;
154	return ns;
155}
156
157/*
158 * is_child_reaper returns true if the pid is the init process
159 * of the current namespace. As this one could be checked before
160 * pid_ns->child_reaper is assigned in copy_process, we check
161 * with the pid number.
162 */
163static inline bool is_child_reaper(struct pid *pid)
164{
165	return pid->numbers[pid->level].nr == 1;
166}
167
168/*
169 * the helpers to get the pid's id seen from different namespaces
170 *
171 * pid_nr()    : global id, i.e. the id seen from the init namespace;
172 * pid_vnr()   : virtual id, i.e. the id seen from the pid namespace of
173 *               current.
174 * pid_nr_ns() : id seen from the ns specified.
175 *
176 * see also task_xid_nr() etc in include/linux/sched.h
177 */
178
179static inline pid_t pid_nr(struct pid *pid)
180{
181	pid_t nr = 0;
182	if (pid)
183		nr = pid->numbers[0].nr;
184	return nr;
185}
186
187pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
188pid_t pid_vnr(struct pid *pid);
189
190#define do_each_pid_task(pid, type, task)				\
191	do {								\
192		if ((pid) != NULL)					\
193			hlist_for_each_entry_rcu((task),		\
194				&(pid)->tasks[type], pid_links[type]) {
195
196			/*
197			 * Both old and new leaders may be attached to
198			 * the same pid in the middle of de_thread().
199			 */
200#define while_each_pid_task(pid, type, task)				\
201				if (type == PIDTYPE_PID)		\
202					break;				\
203			}						\
204	} while (0)
205
206#define do_each_pid_thread(pid, type, task)				\
207	do_each_pid_task(pid, type, task) {				\
208		struct task_struct *tg___ = task;			\
209		for_each_thread(tg___, task) {
210
211#define while_each_pid_thread(pid, type, task)				\
212		}							\
213		task = tg___;						\
214	} while_each_pid_task(pid, type, task)
215
216static inline struct pid *task_pid(struct task_struct *task)
217{
218	return task->thread_pid;
219}
220
221/*
222 * the helpers to get the task's different pids as they are seen
223 * from various namespaces
224 *
225 * task_xid_nr()     : global id, i.e. the id seen from the init namespace;
226 * task_xid_vnr()    : virtual id, i.e. the id seen from the pid namespace of
227 *                     current.
228 * task_xid_nr_ns()  : id seen from the ns specified;
229 *
230 * see also pid_nr() etc in include/linux/pid.h
231 */
232pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type, struct pid_namespace *ns);
233
234static inline pid_t task_pid_nr(struct task_struct *tsk)
235{
236	return tsk->pid;
237}
238
239static inline pid_t task_pid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
240{
241	return __task_pid_nr_ns(tsk, PIDTYPE_PID, ns);
242}
243
244static inline pid_t task_pid_vnr(struct task_struct *tsk)
245{
246	return __task_pid_nr_ns(tsk, PIDTYPE_PID, NULL);
247}
248
249
250static inline pid_t task_tgid_nr(struct task_struct *tsk)
251{
252	return tsk->tgid;
253}
254
255/**
256 * pid_alive - check that a task structure is not stale
257 * @p: Task structure to be checked.
258 *
259 * Test if a process is not yet dead (at most zombie state)
260 * If pid_alive fails, then pointers within the task structure
261 * can be stale and must not be dereferenced.
262 *
263 * Return: 1 if the process is alive. 0 otherwise.
264 */
265static inline int pid_alive(const struct task_struct *p)
266{
267	return p->thread_pid != NULL;
268}
269
270static inline pid_t task_pgrp_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
271{
272	return __task_pid_nr_ns(tsk, PIDTYPE_PGID, ns);
273}
274
275static inline pid_t task_pgrp_vnr(struct task_struct *tsk)
276{
277	return __task_pid_nr_ns(tsk, PIDTYPE_PGID, NULL);
278}
279
280
281static inline pid_t task_session_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
282{
283	return __task_pid_nr_ns(tsk, PIDTYPE_SID, ns);
284}
285
286static inline pid_t task_session_vnr(struct task_struct *tsk)
287{
288	return __task_pid_nr_ns(tsk, PIDTYPE_SID, NULL);
289}
290
291static inline pid_t task_tgid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
292{
293	return __task_pid_nr_ns(tsk, PIDTYPE_TGID, ns);
294}
295
296static inline pid_t task_tgid_vnr(struct task_struct *tsk)
297{
298	return __task_pid_nr_ns(tsk, PIDTYPE_TGID, NULL);
299}
300
301static inline pid_t task_ppid_nr_ns(const struct task_struct *tsk, struct pid_namespace *ns)
302{
303	pid_t pid = 0;
304
305	rcu_read_lock();
306	if (pid_alive(tsk))
307		pid = task_tgid_nr_ns(rcu_dereference(tsk->real_parent), ns);
308	rcu_read_unlock();
309
310	return pid;
311}
312
313static inline pid_t task_ppid_nr(const struct task_struct *tsk)
314{
315	return task_ppid_nr_ns(tsk, &init_pid_ns);
316}
317
318/* Obsolete, do not use: */
319static inline pid_t task_pgrp_nr(struct task_struct *tsk)
320{
321	return task_pgrp_nr_ns(tsk, &init_pid_ns);
322}
323
324/**
325 * is_global_init - check if a task structure is init. Since init
326 * is free to have sub-threads we need to check tgid.
327 * @tsk: Task structure to be checked.
328 *
329 * Check if a task structure is the first user space task the kernel created.
330 *
331 * Return: 1 if the task structure is init. 0 otherwise.
332 */
333static inline int is_global_init(struct task_struct *tsk)
334{
335	return task_tgid_nr(tsk) == 1;
336}
337
338#endif /* _LINUX_PID_H */