1 | /* SPDX-License-Identifier: GPL-2.0 */ |
2 | #ifndef _LINUX_PID_H |
3 | #define _LINUX_PID_H |
4 | |
5 | #include <linux/rculist.h> |
6 | |
7 | enum pid_type |
8 | { |
9 | PIDTYPE_PID, |
10 | PIDTYPE_TGID, |
11 | PIDTYPE_PGID, |
12 | PIDTYPE_SID, |
13 | PIDTYPE_MAX, |
14 | }; |
15 | |
16 | /* |
17 | * What is struct pid? |
18 | * |
19 | * A struct pid is the kernel's internal notion of a process identifier. |
20 | * It refers to individual tasks, process groups, and sessions. While |
21 | * there are processes attached to it the struct pid lives in a hash |
22 | * table, so it and then the processes that it refers to can be found |
23 | * quickly from the numeric pid value. The attached processes may be |
24 | * quickly accessed by following pointers from struct pid. |
25 | * |
26 | * Storing pid_t values in the kernel and referring to them later has a |
27 | * problem. The process originally with that pid may have exited and the |
28 | * pid allocator wrapped, and another process could have come along |
29 | * and been assigned that pid. |
30 | * |
31 | * Referring to user space processes by holding a reference to struct |
32 | * task_struct has a problem. When the user space process exits |
33 | * the now useless task_struct is still kept. A task_struct plus a |
34 | * stack consumes around 10K of low kernel memory. More precisely |
35 | * this is THREAD_SIZE + sizeof(struct task_struct). By comparison |
36 | * a struct pid is about 64 bytes. |
37 | * |
38 | * Holding a reference to struct pid solves both of these problems. |
39 | * It is small so holding a reference does not consume a lot of |
40 | * resources, and since a new struct pid is allocated when the numeric pid |
41 | * value is reused (when pids wrap around) we don't mistakenly refer to new |
42 | * processes. |
43 | */ |
44 | |
45 | |
46 | /* |
47 | * struct upid is used to get the id of the struct pid, as it is |
48 | * seen in particular namespace. Later the struct pid is found with |
49 | * find_pid_ns() using the int nr and struct pid_namespace *ns. |
50 | */ |
51 | |
52 | struct upid { |
53 | int nr; |
54 | struct pid_namespace *ns; |
55 | }; |
56 | |
57 | struct pid |
58 | { |
59 | atomic_t count; |
60 | unsigned int level; |
61 | /* lists of tasks that use this pid */ |
62 | struct hlist_head tasks[PIDTYPE_MAX]; |
63 | struct rcu_head rcu; |
64 | struct upid numbers[1]; |
65 | }; |
66 | |
67 | extern struct pid init_struct_pid; |
68 | |
69 | static inline struct pid *get_pid(struct pid *pid) |
70 | { |
71 | if (pid) |
72 | atomic_inc(&pid->count); |
73 | return pid; |
74 | } |
75 | |
76 | extern void put_pid(struct pid *pid); |
77 | extern struct task_struct *pid_task(struct pid *pid, enum pid_type); |
78 | extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type); |
79 | |
80 | extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type); |
81 | |
82 | /* |
83 | * these helpers must be called with the tasklist_lock write-held. |
84 | */ |
85 | extern void attach_pid(struct task_struct *task, enum pid_type); |
86 | extern void detach_pid(struct task_struct *task, enum pid_type); |
87 | extern void change_pid(struct task_struct *task, enum pid_type, |
88 | struct pid *pid); |
89 | extern void transfer_pid(struct task_struct *old, struct task_struct *new, |
90 | enum pid_type); |
91 | |
92 | struct pid_namespace; |
93 | extern struct pid_namespace init_pid_ns; |
94 | |
95 | /* |
96 | * look up a PID in the hash table. Must be called with the tasklist_lock |
97 | * or rcu_read_lock() held. |
98 | * |
99 | * find_pid_ns() finds the pid in the namespace specified |
100 | * find_vpid() finds the pid by its virtual id, i.e. in the current namespace |
101 | * |
102 | * see also find_task_by_vpid() set in include/linux/sched.h |
103 | */ |
104 | extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns); |
105 | extern struct pid *find_vpid(int nr); |
106 | |
107 | /* |
108 | * Lookup a PID in the hash table, and return with it's count elevated. |
109 | */ |
110 | extern struct pid *find_get_pid(int nr); |
111 | extern struct pid *find_ge_pid(int nr, struct pid_namespace *); |
112 | |
113 | extern struct pid *alloc_pid(struct pid_namespace *ns); |
114 | extern void free_pid(struct pid *pid); |
115 | extern void disable_pid_allocation(struct pid_namespace *ns); |
116 | |
117 | /* |
118 | * ns_of_pid() returns the pid namespace in which the specified pid was |
119 | * allocated. |
120 | * |
121 | * NOTE: |
122 | * ns_of_pid() is expected to be called for a process (task) that has |
123 | * an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid |
124 | * is expected to be non-NULL. If @pid is NULL, caller should handle |
125 | * the resulting NULL pid-ns. |
126 | */ |
127 | static inline struct pid_namespace *ns_of_pid(struct pid *pid) |
128 | { |
129 | struct pid_namespace *ns = NULL; |
130 | if (pid) |
131 | ns = pid->numbers[pid->level].ns; |
132 | return ns; |
133 | } |
134 | |
135 | /* |
136 | * is_child_reaper returns true if the pid is the init process |
137 | * of the current namespace. As this one could be checked before |
138 | * pid_ns->child_reaper is assigned in copy_process, we check |
139 | * with the pid number. |
140 | */ |
141 | static inline bool is_child_reaper(struct pid *pid) |
142 | { |
143 | return pid->numbers[pid->level].nr == 1; |
144 | } |
145 | |
146 | /* |
147 | * the helpers to get the pid's id seen from different namespaces |
148 | * |
149 | * pid_nr() : global id, i.e. the id seen from the init namespace; |
150 | * pid_vnr() : virtual id, i.e. the id seen from the pid namespace of |
151 | * current. |
152 | * pid_nr_ns() : id seen from the ns specified. |
153 | * |
154 | * see also task_xid_nr() etc in include/linux/sched.h |
155 | */ |
156 | |
157 | static inline pid_t pid_nr(struct pid *pid) |
158 | { |
159 | pid_t nr = 0; |
160 | if (pid) |
161 | nr = pid->numbers[0].nr; |
162 | return nr; |
163 | } |
164 | |
165 | pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns); |
166 | pid_t pid_vnr(struct pid *pid); |
167 | |
168 | #define do_each_pid_task(pid, type, task) \ |
169 | do { \ |
170 | if ((pid) != NULL) \ |
171 | hlist_for_each_entry_rcu((task), \ |
172 | &(pid)->tasks[type], pid_links[type]) { |
173 | |
174 | /* |
175 | * Both old and new leaders may be attached to |
176 | * the same pid in the middle of de_thread(). |
177 | */ |
178 | #define while_each_pid_task(pid, type, task) \ |
179 | if (type == PIDTYPE_PID) \ |
180 | break; \ |
181 | } \ |
182 | } while (0) |
183 | |
184 | #define do_each_pid_thread(pid, type, task) \ |
185 | do_each_pid_task(pid, type, task) { \ |
186 | struct task_struct *tg___ = task; \ |
187 | for_each_thread(tg___, task) { |
188 | |
189 | #define while_each_pid_thread(pid, type, task) \ |
190 | } \ |
191 | task = tg___; \ |
192 | } while_each_pid_task(pid, type, task) |
193 | #endif /* _LINUX_PID_H */ |
194 | |