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 | |
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); |
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 | */ |
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 | */ |
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 | |
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 | |