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1 | #ifndef _LINUX_PID_H | |
2 | #define _LINUX_PID_H | |
3 | ||
4 | #include <linux/rculist.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 | ||
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 | * these helpers must be called with the tasklist_lock write-held. | |
92 | */ | |
93 | extern void attach_pid(struct task_struct *task, enum pid_type); | |
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() finds 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 | extern void disable_pid_allocation(struct pid_namespace *ns); | |
125 | ||
126 | /* | |
127 | * ns_of_pid() returns the pid namespace in which the specified pid was | |
128 | * allocated. | |
129 | * | |
130 | * NOTE: | |
131 | * ns_of_pid() is expected to be called for a process (task) that has | |
132 | * an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid | |
133 | * is expected to be non-NULL. If @pid is NULL, caller should handle | |
134 | * the resulting NULL pid-ns. | |
135 | */ | |
136 | static inline struct pid_namespace *ns_of_pid(struct pid *pid) | |
137 | { | |
138 | struct pid_namespace *ns = NULL; | |
139 | if (pid) | |
140 | ns = pid->numbers[pid->level].ns; | |
141 | return ns; | |
142 | } | |
143 | ||
144 | /* | |
145 | * is_child_reaper returns true if the pid is the init process | |
146 | * of the current namespace. As this one could be checked before | |
147 | * pid_ns->child_reaper is assigned in copy_process, we check | |
148 | * with the pid number. | |
149 | */ | |
150 | static inline bool is_child_reaper(struct pid *pid) | |
151 | { | |
152 | return pid->numbers[pid->level].nr == 1; | |
153 | } | |
154 | ||
155 | /* | |
156 | * the helpers to get the pid's id seen from different namespaces | |
157 | * | |
158 | * pid_nr() : global id, i.e. the id seen from the init namespace; | |
159 | * pid_vnr() : virtual id, i.e. the id seen from the pid namespace of | |
160 | * current. | |
161 | * pid_nr_ns() : id seen from the ns specified. | |
162 | * | |
163 | * see also task_xid_nr() etc in include/linux/sched.h | |
164 | */ | |
165 | ||
166 | static inline pid_t pid_nr(struct pid *pid) | |
167 | { | |
168 | pid_t nr = 0; | |
169 | if (pid) | |
170 | nr = pid->numbers[0].nr; | |
171 | return nr; | |
172 | } | |
173 | ||
174 | pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns); | |
175 | pid_t pid_vnr(struct pid *pid); | |
176 | ||
177 | #define do_each_pid_task(pid, type, task) \ | |
178 | do { \ | |
179 | if ((pid) != NULL) \ | |
180 | hlist_for_each_entry_rcu((task), \ | |
181 | &(pid)->tasks[type], pids[type].node) { | |
182 | ||
183 | /* | |
184 | * Both old and new leaders may be attached to | |
185 | * the same pid in the middle of de_thread(). | |
186 | */ | |
187 | #define while_each_pid_task(pid, type, task) \ | |
188 | if (type == PIDTYPE_PID) \ | |
189 | break; \ | |
190 | } \ | |
191 | } while (0) | |
192 | ||
193 | #define do_each_pid_thread(pid, type, task) \ | |
194 | do_each_pid_task(pid, type, task) { \ | |
195 | struct task_struct *tg___ = task; \ | |
196 | for_each_thread(tg___, task) { | |
197 | ||
198 | #define while_each_pid_thread(pid, type, task) \ | |
199 | } \ | |
200 | task = tg___; \ | |
201 | } while_each_pid_task(pid, type, task) | |
202 | #endif /* _LINUX_PID_H */ |