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
9 enum 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
54 struct upid {
55 int nr;
56 struct pid_namespace *ns;
57 };
58
59 struct 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
73 extern struct pid init_struct_pid;
74
75 extern const struct file_operations pidfd_fops;
76
77 struct file;
78
79 extern struct pid *pidfd_pid(const struct file *file);
80 struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags);
81 struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags);
82 int pidfd_create(struct pid *pid, unsigned int flags);
83
get_pid(struct pid * pid)84 static inline struct pid *get_pid(struct pid *pid)
85 {
86 if (pid)
87 refcount_inc(&pid->count);
88 return pid;
89 }
90
91 extern void put_pid(struct pid *pid);
92 extern struct task_struct *pid_task(struct pid *pid, enum pid_type);
pid_has_task(struct pid * pid,enum pid_type type)93 static inline bool pid_has_task(struct pid *pid, enum pid_type type)
94 {
95 return !hlist_empty(&pid->tasks[type]);
96 }
97 extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type);
98
99 extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
100
101 /*
102 * these helpers must be called with the tasklist_lock write-held.
103 */
104 extern void attach_pid(struct task_struct *task, enum pid_type);
105 extern void detach_pid(struct task_struct *task, enum pid_type);
106 extern void change_pid(struct task_struct *task, enum pid_type,
107 struct pid *pid);
108 extern void exchange_tids(struct task_struct *task, struct task_struct *old);
109 extern void transfer_pid(struct task_struct *old, struct task_struct *new,
110 enum pid_type);
111
112 struct pid_namespace;
113 extern struct pid_namespace init_pid_ns;
114
115 extern int pid_max;
116 extern int pid_max_min, pid_max_max;
117
118 /*
119 * look up a PID in the hash table. Must be called with the tasklist_lock
120 * or rcu_read_lock() held.
121 *
122 * find_pid_ns() finds the pid in the namespace specified
123 * find_vpid() finds the pid by its virtual id, i.e. in the current namespace
124 *
125 * see also find_task_by_vpid() set in include/linux/sched.h
126 */
127 extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns);
128 extern struct pid *find_vpid(int nr);
129
130 /*
131 * Lookup a PID in the hash table, and return with it's count elevated.
132 */
133 extern struct pid *find_get_pid(int nr);
134 extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
135
136 extern struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
137 size_t set_tid_size);
138 extern void free_pid(struct pid *pid);
139 extern void disable_pid_allocation(struct pid_namespace *ns);
140
141 /*
142 * ns_of_pid() returns the pid namespace in which the specified pid was
143 * allocated.
144 *
145 * NOTE:
146 * ns_of_pid() is expected to be called for a process (task) that has
147 * an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid
148 * is expected to be non-NULL. If @pid is NULL, caller should handle
149 * the resulting NULL pid-ns.
150 */
ns_of_pid(struct pid * pid)151 static inline struct pid_namespace *ns_of_pid(struct pid *pid)
152 {
153 struct pid_namespace *ns = NULL;
154 if (pid)
155 ns = pid->numbers[pid->level].ns;
156 return ns;
157 }
158
159 /*
160 * is_child_reaper returns true if the pid is the init process
161 * of the current namespace. As this one could be checked before
162 * pid_ns->child_reaper is assigned in copy_process, we check
163 * with the pid number.
164 */
is_child_reaper(struct pid * pid)165 static inline bool is_child_reaper(struct pid *pid)
166 {
167 return pid->numbers[pid->level].nr == 1;
168 }
169
170 /*
171 * the helpers to get the pid's id seen from different namespaces
172 *
173 * pid_nr() : global id, i.e. the id seen from the init namespace;
174 * pid_vnr() : virtual id, i.e. the id seen from the pid namespace of
175 * current.
176 * pid_nr_ns() : id seen from the ns specified.
177 *
178 * see also task_xid_nr() etc in include/linux/sched.h
179 */
180
pid_nr(struct pid * pid)181 static inline pid_t pid_nr(struct pid *pid)
182 {
183 pid_t nr = 0;
184 if (pid)
185 nr = pid->numbers[0].nr;
186 return nr;
187 }
188
189 pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
190 pid_t pid_vnr(struct pid *pid);
191
192 #define do_each_pid_task(pid, type, task) \
193 do { \
194 if ((pid) != NULL) \
195 hlist_for_each_entry_rcu((task), \
196 &(pid)->tasks[type], pid_links[type]) {
197
198 /*
199 * Both old and new leaders may be attached to
200 * the same pid in the middle of de_thread().
201 */
202 #define while_each_pid_task(pid, type, task) \
203 if (type == PIDTYPE_PID) \
204 break; \
205 } \
206 } while (0)
207
208 #define do_each_pid_thread(pid, type, task) \
209 do_each_pid_task(pid, type, task) { \
210 struct task_struct *tg___ = task; \
211 for_each_thread(tg___, task) {
212
213 #define while_each_pid_thread(pid, type, task) \
214 } \
215 task = tg___; \
216 } while_each_pid_task(pid, type, task)
217 #endif /* _LINUX_PID_H */
218