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 };
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
50 struct 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
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 struct pid_link
70 {
71 struct hlist_node node;
72 struct pid *pid;
73 };
74
get_pid(struct pid * pid)75 static inline struct pid *get_pid(struct pid *pid)
76 {
77 if (pid)
78 atomic_inc(&pid->count);
79 return pid;
80 }
81
82 extern void put_pid(struct pid *pid);
83 extern struct task_struct *pid_task(struct pid *pid, enum pid_type);
84 extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type);
85
86 extern 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 */
91 extern void attach_pid(struct task_struct *task, enum pid_type);
92 extern void detach_pid(struct task_struct *task, enum pid_type);
93 extern void change_pid(struct task_struct *task, enum pid_type,
94 struct pid *pid);
95 extern void transfer_pid(struct task_struct *old, struct task_struct *new,
96 enum pid_type);
97
98 struct pid_namespace;
99 extern 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 */
110 extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns);
111 extern struct pid *find_vpid(int nr);
112
113 /*
114 * Lookup a PID in the hash table, and return with it's count elevated.
115 */
116 extern struct pid *find_get_pid(int nr);
117 extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
118 int next_pidmap(struct pid_namespace *pid_ns, unsigned int last);
119
120 extern struct pid *alloc_pid(struct pid_namespace *ns);
121 extern void free_pid(struct pid *pid);
122 extern 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 */
ns_of_pid(struct pid * pid)134 static 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 */
is_child_reaper(struct pid * pid)148 static 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
pid_nr(struct pid * pid)164 static 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
172 pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
173 pid_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