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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 : 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[];
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 : int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret);
84 :
85 : static inline struct pid *get_pid(struct pid *pid)
86 : {
87 32 : if (pid)
88 16 : refcount_inc(&pid->count);
89 32 : return pid;
90 : }
91 :
92 : extern void put_pid(struct pid *pid);
93 : extern struct task_struct *pid_task(struct pid *pid, enum pid_type);
94 : static inline bool pid_has_task(struct pid *pid, enum pid_type type)
95 : {
96 : return !hlist_empty(&pid->tasks[type]);
97 : }
98 : extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type);
99 :
100 : extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
101 :
102 : /*
103 : * these helpers must be called with the tasklist_lock write-held.
104 : */
105 : extern void attach_pid(struct task_struct *task, enum pid_type);
106 : extern void detach_pid(struct task_struct *task, enum pid_type);
107 : extern void change_pid(struct task_struct *task, enum pid_type,
108 : struct pid *pid);
109 : extern void exchange_tids(struct task_struct *task, struct task_struct *old);
110 : extern void transfer_pid(struct task_struct *old, struct task_struct *new,
111 : enum pid_type);
112 :
113 : struct pid_namespace;
114 : extern struct pid_namespace init_pid_ns;
115 :
116 : extern int pid_max;
117 : extern int pid_max_min, pid_max_max;
118 :
119 : /*
120 : * look up a PID in the hash table. Must be called with the tasklist_lock
121 : * or rcu_read_lock() held.
122 : *
123 : * find_pid_ns() finds the pid in the namespace specified
124 : * find_vpid() finds the pid by its virtual id, i.e. in the current namespace
125 : *
126 : * see also find_task_by_vpid() set in include/linux/sched.h
127 : */
128 : extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns);
129 : extern struct pid *find_vpid(int nr);
130 :
131 : /*
132 : * Lookup a PID in the hash table, and return with it's count elevated.
133 : */
134 : extern struct pid *find_get_pid(int nr);
135 : extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
136 :
137 : extern struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
138 : size_t set_tid_size);
139 : extern void free_pid(struct pid *pid);
140 : extern void disable_pid_allocation(struct pid_namespace *ns);
141 :
142 : /*
143 : * ns_of_pid() returns the pid namespace in which the specified pid was
144 : * allocated.
145 : *
146 : * NOTE:
147 : * ns_of_pid() is expected to be called for a process (task) that has
148 : * an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid
149 : * is expected to be non-NULL. If @pid is NULL, caller should handle
150 : * the resulting NULL pid-ns.
151 : */
152 : static inline struct pid_namespace *ns_of_pid(struct pid *pid)
153 : {
154 : struct pid_namespace *ns = NULL;
155 : if (pid)
156 : ns = pid->numbers[pid->level].ns;
157 : return ns;
158 : }
159 :
160 : /*
161 : * is_child_reaper returns true if the pid is the init process
162 : * of the current namespace. As this one could be checked before
163 : * pid_ns->child_reaper is assigned in copy_process, we check
164 : * with the pid number.
165 : */
166 : static inline bool is_child_reaper(struct pid *pid)
167 : {
168 : return pid->numbers[pid->level].nr == 1;
169 : }
170 :
171 : /*
172 : * the helpers to get the pid's id seen from different namespaces
173 : *
174 : * pid_nr() : global id, i.e. the id seen from the init namespace;
175 : * pid_vnr() : virtual id, i.e. the id seen from the pid namespace of
176 : * current.
177 : * pid_nr_ns() : id seen from the ns specified.
178 : *
179 : * see also task_xid_nr() etc in include/linux/sched.h
180 : */
181 :
182 : static inline pid_t pid_nr(struct pid *pid)
183 : {
184 : pid_t nr = 0;
185 : if (pid)
186 : nr = pid->numbers[0].nr;
187 : return nr;
188 : }
189 :
190 : pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
191 : pid_t pid_vnr(struct pid *pid);
192 :
193 : #define do_each_pid_task(pid, type, task) \
194 : do { \
195 : if ((pid) != NULL) \
196 : hlist_for_each_entry_rcu((task), \
197 : &(pid)->tasks[type], pid_links[type]) {
198 :
199 : /*
200 : * Both old and new leaders may be attached to
201 : * the same pid in the middle of de_thread().
202 : */
203 : #define while_each_pid_task(pid, type, task) \
204 : if (type == PIDTYPE_PID) \
205 : break; \
206 : } \
207 : } while (0)
208 :
209 : #define do_each_pid_thread(pid, type, task) \
210 : do_each_pid_task(pid, type, task) { \
211 : struct task_struct *tg___ = task; \
212 : for_each_thread(tg___, task) {
213 :
214 : #define while_each_pid_thread(pid, type, task) \
215 : } \
216 : task = tg___; \
217 : } while_each_pid_task(pid, type, task)
218 : #endif /* _LINUX_PID_H */
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