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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 | |
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 | |
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, 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 */ |
192 |
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