1 #ifndef _LINUX_PID_H
2 #define _LINUX_PID_H
3
4 #include <linux/rcupdate.h>
5
6 enum pid_type
7 {
8 PIDTYPE_PID,
9 PIDTYPE_PGID,
10 PIDTYPE_SID,
11 PIDTYPE_MAX,
12 /* only valid to __task_pid_nr_ns() */
13 __PIDTYPE_TGID
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 /* Try to keep pid_chain in the same cacheline as nr for find_vpid */
54 int nr;
55 struct pid_namespace *ns;
56 struct hlist_node pid_chain;
57 };
58
59 struct pid
60 {
61 atomic_t count;
62 unsigned int level;
63 /* lists of tasks that use this pid */
64 struct hlist_head tasks[PIDTYPE_MAX];
65 struct rcu_head rcu;
66 struct upid numbers[1];
67 };
68
69 extern struct pid init_struct_pid;
70
71 struct pid_link
72 {
73 struct hlist_node node;
74 struct pid *pid;
75 };
76
get_pid(struct pid * pid)77 static inline struct pid *get_pid(struct pid *pid)
78 {
79 if (pid)
80 atomic_inc(&pid->count);
81 return pid;
82 }
83
84 extern void put_pid(struct pid *pid);
85 extern struct task_struct *pid_task(struct pid *pid, enum pid_type);
86 extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type);
87
88 extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
89
90 /*
91 * attach_pid() and detach_pid() must be called with the tasklist_lock
92 * write-held.
93 */
94 extern void attach_pid(struct task_struct *task, enum pid_type type,
95 struct pid *pid);
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 int next_pidmap(struct pid_namespace *pid_ns, unsigned int last);
123
124 extern struct pid *alloc_pid(struct pid_namespace *ns);
125 extern void free_pid(struct pid *pid);
126 extern void disable_pid_allocation(struct pid_namespace *ns);
127
128 /*
129 * ns_of_pid() returns the pid namespace in which the specified pid was
130 * allocated.
131 *
132 * NOTE:
133 * ns_of_pid() is expected to be called for a process (task) that has
134 * an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid
135 * is expected to be non-NULL. If @pid is NULL, caller should handle
136 * the resulting NULL pid-ns.
137 */
ns_of_pid(struct pid * pid)138 static inline struct pid_namespace *ns_of_pid(struct pid *pid)
139 {
140 struct pid_namespace *ns = NULL;
141 if (pid)
142 ns = pid->numbers[pid->level].ns;
143 return ns;
144 }
145
146 /*
147 * is_child_reaper returns true if the pid is the init process
148 * of the current namespace. As this one could be checked before
149 * pid_ns->child_reaper is assigned in copy_process, we check
150 * with the pid number.
151 */
is_child_reaper(struct pid * pid)152 static inline bool is_child_reaper(struct pid *pid)
153 {
154 return pid->numbers[pid->level].nr == 1;
155 }
156
157 /*
158 * the helpers to get the pid's id seen from different namespaces
159 *
160 * pid_nr() : global id, i.e. the id seen from the init namespace;
161 * pid_vnr() : virtual id, i.e. the id seen from the pid namespace of
162 * current.
163 * pid_nr_ns() : id seen from the ns specified.
164 *
165 * see also task_xid_nr() etc in include/linux/sched.h
166 */
167
pid_nr(struct pid * pid)168 static inline pid_t pid_nr(struct pid *pid)
169 {
170 pid_t nr = 0;
171 if (pid)
172 nr = pid->numbers[0].nr;
173 return nr;
174 }
175
176 pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
177 pid_t pid_vnr(struct pid *pid);
178
179 #define do_each_pid_task(pid, type, task) \
180 do { \
181 if ((pid) != NULL) \
182 hlist_for_each_entry_rcu((task), \
183 &(pid)->tasks[type], pids[type].node) {
184
185 /*
186 * Both old and new leaders may be attached to
187 * the same pid in the middle of de_thread().
188 */
189 #define while_each_pid_task(pid, type, task) \
190 if (type == PIDTYPE_PID) \
191 break; \
192 } \
193 } while (0)
194
195 #define do_each_pid_thread(pid, type, task) \
196 do_each_pid_task(pid, type, task) { \
197 struct task_struct *tg___ = task; \
198 do {
199
200 #define while_each_pid_thread(pid, type, task) \
201 } while_each_thread(tg___, task); \
202 task = tg___; \
203 } while_each_pid_task(pid, type, task)
204 #endif /* _LINUX_PID_H */
205