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