4 #include <linux/rcupdate.h>
15  * What is struct pid?
17  * A struct pid is the kernel's internal notion of a process identifier.
19  * there are processes attached to it the struct pid lives in a hash
21  * quickly from the numeric pid value.  The attached processes may be
22  * quickly accessed by following pointers from struct pid.
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.
34  * a struct pid is about 64 bytes.
36  * Holding a reference to struct pid solves both of these problems.
38  * resources, and since a new struct pid is allocated when the numeric pid
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
57 struct pid  struct
61 	/* lists of tasks that use this pid */  argument
67 extern struct pid init_struct_pid;  argument
72 	struct pid *pid;  member
75 static inline struct pid *get_pid(struct pid *pid)  in get_pid()  argument
77 	if (pid)  in get_pid()
78 		atomic_inc(&pid->count);  in get_pid()
79 	return pid;  in get_pid()
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);
86 extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
89  * these helpers must be called with the tasklist_lock write-held.
94 			struct pid *pid);
102  * look up a PID in the hash table. Must be called with the tasklist_lock
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
108  * see also find_task_by_vpid() set in include/linux/sched.h
110 extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns);
111 extern struct pid *find_vpid(int nr);
114  * Lookup a PID in the hash table, and return with it's count elevated.
116 extern struct pid *find_get_pid(int nr);
117 extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
120 extern struct pid *alloc_pid(struct pid_namespace *ns);
121 extern void free_pid(struct pid *pid);
125  * ns_of_pid() returns the pid namespace in which the specified pid was
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.
134 static inline struct pid_namespace *ns_of_pid(struct pid *pid)  in ns_of_pid()  argument
137 	if (pid)  in ns_of_pid()
138 		ns = pid->numbers[pid->level].ns;  in ns_of_pid()
143  * is_child_reaper returns true if the pid is the init process
145  * pid_ns->child_reaper is assigned in copy_process, we check
146  * with the pid number.
148 static inline bool is_child_reaper(struct pid *pid)  in is_child_reaper()  argument
150 	return pid->numbers[pid->level].nr == 1;  in is_child_reaper()
154  * the helpers to get the pid's id seen from different namespaces
157  * pid_vnr()   : virtual id, i.e. the id seen from the pid namespace of
161  * see also task_xid_nr() etc in include/linux/sched.h
164 static inline pid_t pid_nr(struct pid *pid)  in pid_nr()  argument
167 	if (pid)  in pid_nr()
168 		nr = pid->numbers[0].nr;  in pid_nr()
172 pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
173 pid_t pid_vnr(struct pid *pid);
175 #define do_each_pid_task(pid, type, task)				\  argument
177 		if ((pid) != NULL)					\
179 				&(pid)->tasks[type], pids[type].node) {
183 			 * the same pid in the middle of de_thread().
185 #define while_each_pid_task(pid, type, task)				\  argument
191 #define do_each_pid_thread(pid, type, task)				\  argument
192 	do_each_pid_task(pid, type, task) {				\
196 #define while_each_pid_thread(pid, type, task)				\  argument
199 	} while_each_pid_task(pid, type, task)