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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 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 : :
75 : : static inline struct pid *get_pid(struct pid *pid)
76 : : {
77 [ + + ][ + - ]: 4094169 : if (pid)
[ + + ][ + - ]
[ - + ][ + - ]
[ + - ][ + - ]
[ # # + -
+ - - + ]
[ # # # # ]
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78 : 2118720 : 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 : : */
134 : : static inline struct pid_namespace *ns_of_pid(struct pid *pid)
135 : : {
136 : : struct pid_namespace *ns = NULL;
137 [ + + # # ]: 74671812 : if (pid)
[ + - ][ + + ]
[ + ][ + - ]
[ + - ]
138 : 75339635 : 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 : : */
148 : : static inline bool is_child_reaper(struct pid *pid)
149 : : {
150 : 2206195 : 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 : :
164 : : static inline pid_t pid_nr(struct pid *pid)
165 : : {
166 : : pid_t nr = 0;
167 [ # # # # ]: 1104223 : if (pid)
[ + - ]
168 : 1104223 : 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 */
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