1#ifndef _LINUX_PID_H
2#define _LINUX_PID_H
3
4#include <linux/rcupdate.h>
5
6enum pid_type
7{
8	PIDTYPE_PID,
9	PIDTYPE_PGID,
10	PIDTYPE_SID,
11	PIDTYPE_MAX
12};
13
14/*
15 * What is struct pid?
16 *
17 * A struct pid is the kernel's internal notion of a process identifier.
18 * It refers to individual tasks, process groups, and sessions.  While
19 * there are processes attached to it the struct pid lives in a hash
20 * table, so it and then the processes that it refers to can be found
21 * quickly from the numeric pid value.  The attached processes may be
22 * quickly accessed by following pointers from struct pid.
23 *
24 * Storing pid_t values in the kernel and referring to them later has a
25 * problem.  The process originally with that pid may have exited and the
26 * pid allocator wrapped, and another process could have come along
27 * and been assigned that pid.
28 *
29 * Referring to user space processes by holding a reference to struct
30 * task_struct has a problem.  When the user space process exits
31 * the now useless task_struct is still kept.  A task_struct plus a
32 * stack consumes around 10K of low kernel memory.  More precisely
33 * this is THREAD_SIZE + sizeof(struct task_struct).  By comparison
34 * a struct pid is about 64 bytes.
35 *
36 * Holding a reference to struct pid solves both of these problems.
37 * It is small so holding a reference does not consume a lot of
38 * resources, and since a new struct pid is allocated when the numeric pid
39 * value is reused (when pids wrap around) we don't mistakenly refer to new
40 * processes.
41 */
42
43
44/*
45 * struct upid is used to get the id of the struct pid, as it is
46 * seen in particular namespace. Later the struct pid is found with
47 * find_pid_ns() using the int nr and struct pid_namespace *ns.
48 */
49
50struct upid {
51	/* Try to keep pid_chain in the same cacheline as nr for find_vpid */
52	int nr;
53	struct pid_namespace *ns;
54	struct hlist_node pid_chain;
55};
56
57struct 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
67extern struct pid init_struct_pid;
68
69struct pid_link
70{
71	struct hlist_node node;
72	struct pid *pid;
73};
74
75static inline struct pid *get_pid(struct pid *pid)
76{
77	if (pid)
78		atomic_inc(&pid->count);
79	return pid;
80}
81
82extern void put_pid(struct pid *pid);
83extern struct task_struct *pid_task(struct pid *pid, enum pid_type);
84extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type);
85
86extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
87
88/*
89 * these helpers must be called with the tasklist_lock write-held.
90 */
91extern void attach_pid(struct task_struct *task, enum pid_type);
92extern void detach_pid(struct task_struct *task, enum pid_type);
93extern void change_pid(struct task_struct *task, enum pid_type,
94			struct pid *pid);
95extern void transfer_pid(struct task_struct *old, struct task_struct *new,
96			 enum pid_type);
97
98struct pid_namespace;
99extern struct pid_namespace init_pid_ns;
100
101/*
102 * look up a PID in the hash table. Must be called with the tasklist_lock
103 * or rcu_read_lock() held.
104 *
105 * find_pid_ns() finds the pid in the namespace specified
106 * find_vpid() finds the pid by its virtual id, i.e. in the current namespace
107 *
108 * see also find_task_by_vpid() set in include/linux/sched.h
109 */
110extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns);
111extern struct pid *find_vpid(int nr);
112
113/*
114 * Lookup a PID in the hash table, and return with it's count elevated.
115 */
116extern struct pid *find_get_pid(int nr);
117extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
118int next_pidmap(struct pid_namespace *pid_ns, unsigned int last);
119
120extern struct pid *alloc_pid(struct pid_namespace *ns);
121extern void free_pid(struct pid *pid);
122extern void disable_pid_allocation(struct pid_namespace *ns);
123
124/*
125 * ns_of_pid() returns the pid namespace in which the specified pid was
126 * allocated.
127 *
128 * NOTE:
129 * 	ns_of_pid() is expected to be called for a process (task) that has
130 * 	an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid
131 * 	is expected to be non-NULL. If @pid is NULL, caller should handle
132 * 	the resulting NULL pid-ns.
133 */
134static inline struct pid_namespace *ns_of_pid(struct pid *pid)
135{
136	struct pid_namespace *ns = NULL;
137	if (pid)
138		ns = pid->numbers[pid->level].ns;
139	return ns;
140}
141
142/*
143 * is_child_reaper returns true if the pid is the init process
144 * of the current namespace. As this one could be checked before
145 * pid_ns->child_reaper is assigned in copy_process, we check
146 * with the pid number.
147 */
148static inline bool is_child_reaper(struct pid *pid)
149{
150	return pid->numbers[pid->level].nr == 1;
151}
152
153/*
154 * the helpers to get the pid's id seen from different namespaces
155 *
156 * pid_nr()    : global id, i.e. the id seen from the init namespace;
157 * pid_vnr()   : virtual id, i.e. the id seen from the pid namespace of
158 *               current.
159 * pid_nr_ns() : id seen from the ns specified.
160 *
161 * see also task_xid_nr() etc in include/linux/sched.h
162 */
163
164static inline pid_t pid_nr(struct pid *pid)
165{
166	pid_t nr = 0;
167	if (pid)
168		nr = pid->numbers[0].nr;
169	return nr;
170}
171
172pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
173pid_t pid_vnr(struct pid *pid);
174
175#define do_each_pid_task(pid, type, task)				\
176	do {								\
177		if ((pid) != NULL)					\
178			hlist_for_each_entry_rcu((task),		\
179				&(pid)->tasks[type], pids[type].node) {
180
181			/*
182			 * Both old and new leaders may be attached to
183			 * the same pid in the middle of de_thread().
184			 */
185#define while_each_pid_task(pid, type, task)				\
186				if (type == PIDTYPE_PID)		\
187					break;				\
188			}						\
189	} while (0)
190
191#define do_each_pid_thread(pid, type, task)				\
192	do_each_pid_task(pid, type, task) {				\
193		struct task_struct *tg___ = task;			\
194		do {
195
196#define while_each_pid_thread(pid, type, task)				\
197		} while_each_thread(tg___, task);			\
198		task = tg___;						\
199	} while_each_pid_task(pid, type, task)
200#endif /* _LINUX_PID_H */
201