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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 : : /* lists of tasks that use this pid */
64 : : struct hlist_head tasks[PIDTYPE_MAX];
65 : : /* wait queue for pidfd notifications */
66 : : wait_queue_head_t wait_pidfd;
67 : : struct rcu_head rcu;
68 : : struct upid numbers[1];
69 : : };
70 : :
71 : : extern struct pid init_struct_pid;
72 : :
73 : : extern const struct file_operations pidfd_fops;
74 : :
75 : : struct file;
76 : :
77 : : extern struct pid *pidfd_pid(const struct file *file);
78 : :
79 : : static inline struct pid *get_pid(struct pid *pid)
80 : : {
81 [ + + + + : 3896119 : if (pid)
+ + + - +
+ + + ]
82 : 2652376 : refcount_inc(&pid->count);
83 : : return pid;
84 : : }
85 : :
86 : : extern void put_pid(struct pid *pid);
87 : : extern struct task_struct *pid_task(struct pid *pid, enum pid_type);
88 : : extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type);
89 : :
90 : : extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
91 : :
92 : : /*
93 : : * these helpers must be called with the tasklist_lock write-held.
94 : : */
95 : : extern void attach_pid(struct task_struct *task, enum pid_type);
96 : : extern void detach_pid(struct task_struct *task, enum pid_type);
97 : : extern void change_pid(struct task_struct *task, enum pid_type,
98 : : struct pid *pid);
99 : : extern void transfer_pid(struct task_struct *old, struct task_struct *new,
100 : : enum pid_type);
101 : :
102 : : struct pid_namespace;
103 : : extern struct pid_namespace init_pid_ns;
104 : :
105 : : /*
106 : : * look up a PID in the hash table. Must be called with the tasklist_lock
107 : : * or rcu_read_lock() held.
108 : : *
109 : : * find_pid_ns() finds the pid in the namespace specified
110 : : * find_vpid() finds the pid by its virtual id, i.e. in the current namespace
111 : : *
112 : : * see also find_task_by_vpid() set in include/linux/sched.h
113 : : */
114 : : extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns);
115 : : extern struct pid *find_vpid(int nr);
116 : :
117 : : /*
118 : : * Lookup a PID in the hash table, and return with it's count elevated.
119 : : */
120 : : extern struct pid *find_get_pid(int nr);
121 : : extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
122 : :
123 : : extern struct pid *alloc_pid(struct pid_namespace *ns);
124 : : extern void free_pid(struct pid *pid);
125 : : extern void disable_pid_allocation(struct pid_namespace *ns);
126 : :
127 : : /*
128 : : * ns_of_pid() returns the pid namespace in which the specified pid was
129 : : * allocated.
130 : : *
131 : : * NOTE:
132 : : * ns_of_pid() is expected to be called for a process (task) that has
133 : : * an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid
134 : : * is expected to be non-NULL. If @pid is NULL, caller should handle
135 : : * the resulting NULL pid-ns.
136 : : */
137 : : static inline struct pid_namespace *ns_of_pid(struct pid *pid)
138 : : {
139 : : struct pid_namespace *ns = NULL;
140 [ + + + + : 2896881 : if (pid)
+ + + - +
+ ]
141 : 2896114 : ns = pid->numbers[pid->level].ns;
142 : : return ns;
143 : : }
144 : :
145 : : /*
146 : : * is_child_reaper returns true if the pid is the init process
147 : : * of the current namespace. As this one could be checked before
148 : : * pid_ns->child_reaper is assigned in copy_process, we check
149 : : * with the pid number.
150 : : */
151 : : static inline bool is_child_reaper(struct pid *pid)
152 : : {
153 : 391509 : return pid->numbers[pid->level].nr == 1;
154 : : }
155 : :
156 : : /*
157 : : * the helpers to get the pid's id seen from different namespaces
158 : : *
159 : : * pid_nr() : global id, i.e. the id seen from the init namespace;
160 : : * pid_vnr() : virtual id, i.e. the id seen from the pid namespace of
161 : : * current.
162 : : * pid_nr_ns() : id seen from the ns specified.
163 : : *
164 : : * see also task_xid_nr() etc in include/linux/sched.h
165 : : */
166 : :
167 : : static inline pid_t pid_nr(struct pid *pid)
168 : : {
169 : : pid_t nr = 0;
170 [ + - # # ]: 201516 : if (pid)
171 : 201519 : nr = pid->numbers[0].nr;
172 : : return nr;
173 : : }
174 : :
175 : : pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
176 : : pid_t pid_vnr(struct pid *pid);
177 : :
178 : : #define do_each_pid_task(pid, type, task) \
179 : : do { \
180 : : if ((pid) != NULL) \
181 : : hlist_for_each_entry_rcu((task), \
182 : : &(pid)->tasks[type], pid_links[type]) {
183 : :
184 : : /*
185 : : * Both old and new leaders may be attached to
186 : : * the same pid in the middle of de_thread().
187 : : */
188 : : #define while_each_pid_task(pid, type, task) \
189 : : if (type == PIDTYPE_PID) \
190 : : break; \
191 : : } \
192 : : } while (0)
193 : :
194 : : #define do_each_pid_thread(pid, type, task) \
195 : : do_each_pid_task(pid, type, task) { \
196 : : struct task_struct *tg___ = task; \
197 : : for_each_thread(tg___, task) {
198 : :
199 : : #define while_each_pid_thread(pid, type, task) \
200 : : } \
201 : : task = tg___; \
202 : : } while_each_pid_task(pid, type, task)
203 : : #endif /* _LINUX_PID_H */
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