Line data Source code
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 refering 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 1 :
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 1 :
69 : struct pid_link
70 : {
71 : struct hlist_node node;
72 : struct pid *pid;
73 : };
74 :
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 : * attach_pid() and detach_pid() must be called with the tasklist_lock
90 : * write-held.
91 : */
92 : extern void attach_pid(struct task_struct *task, enum pid_type type,
93 : struct pid *pid);
94 : extern void detach_pid(struct task_struct *task, enum pid_type);
95 : extern void change_pid(struct task_struct *task, enum pid_type,
96 : struct pid *pid);
97 : extern void transfer_pid(struct task_struct *old, struct task_struct *new,
98 : enum pid_type);
99 :
100 : struct pid_namespace;
101 : extern struct pid_namespace init_pid_ns;
102 :
103 : /*
104 : * look up a PID in the hash table. Must be called with the tasklist_lock
105 : * or rcu_read_lock() held.
106 : *
107 : * find_pid_ns() finds the pid in the namespace specified
108 : * find_vpid() finr the pid by its virtual id, i.e. in the current namespace
109 : *
110 : * see also find_task_by_vpid() set in include/linux/sched.h
111 : */
112 : extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns);
113 : extern struct pid *find_vpid(int nr);
114 :
115 : /*
116 : * Lookup a PID in the hash table, and return with it's count elevated.
117 : */
118 : extern struct pid *find_get_pid(int nr);
119 : extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
120 : int next_pidmap(struct pid_namespace *pid_ns, unsigned int last);
121 :
122 : extern struct pid *alloc_pid(struct pid_namespace *ns);
123 : extern void free_pid(struct pid *pid);
124 :
125 : /*
126 : * ns_of_pid() returns the pid namespace in which the specified pid was
127 : * allocated.
128 : *
129 : * NOTE:
130 : * ns_of_pid() is expected to be called for a process (task) that has
131 : * an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid
132 : * is expected to be non-NULL. If @pid is NULL, caller should handle
133 : * the resulting NULL pid-ns.
134 : */
135 : static inline struct pid_namespace *ns_of_pid(struct pid *pid)
136 : {
137 : struct pid_namespace *ns = NULL;
138 : if (pid)
139 : ns = pid->numbers[pid->level].ns;
140 : return ns;
141 : }
142 :
143 : /*
144 : * the helpers to get the pid's id seen from different namespaces
145 : *
146 : * pid_nr() : global id, i.e. the id seen from the init namespace;
147 : * pid_vnr() : virtual id, i.e. the id seen from the pid namespace of
148 : * current.
149 : * pid_nr_ns() : id seen from the ns specified.
150 : *
151 : * see also task_xid_nr() etc in include/linux/sched.h
152 : */
153 :
154 : static inline pid_t pid_nr(struct pid *pid)
155 : {
156 : pid_t nr = 0;
157 : if (pid)
158 : nr = pid->numbers[0].nr;
159 : return nr;
160 : }
161 :
162 : pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
163 : pid_t pid_vnr(struct pid *pid);
164 :
165 : #define do_each_pid_task(pid, type, task) \
166 : do { \
167 : struct hlist_node *pos___; \
168 : if ((pid) != NULL) \
169 : hlist_for_each_entry_rcu((task), pos___, \
170 : &(pid)->tasks[type], pids[type].node) {
171 :
172 : /*
173 : * Both old and new leaders may be attached to
174 : * the same pid in the middle of de_thread().
175 : */
176 : #define while_each_pid_task(pid, type, task) \
177 : if (type == PIDTYPE_PID) \
178 : break; \
179 : } \
180 : } while (0)
181 :
182 : #define do_each_pid_thread(pid, type, task) \
183 : do_each_pid_task(pid, type, task) { \
184 : struct task_struct *tg___ = task; \
185 : do {
186 :
187 : #define while_each_pid_thread(pid, type, task) \
188 : } while_each_thread(tg___, task); \
189 : task = tg___; \
190 : } while_each_pid_task(pid, type, task)
191 : #endif /* _LINUX_PID_H */
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