13  * What is struct pid?
15  * A struct pid is the kernel's internal notion of a process identifier.
17  * there are processes attached to it the struct pid lives in a hash
19  * quickly from the numeric pid value.  The attached processes may be
20  * quickly accessed by following pointers from struct pid.
23  * problem.  The process originally with that pid may have exited and the
24  * pid allocator wrapped, and another process could have come along
25  * and been assigned that pid.
32  * a struct pid is about 64 bytes.
34  * Holding a reference to struct pid solves both of these problems.
36  * resources, and since a new struct pid is allocated when the numeric pid
43  * struct upid is used to get the id of the struct pid, as it is
44  * seen in particular namespace. Later the struct pid is found with
55 struct pid  struct
63 	/* lists of tasks that use this pid */  argument
73 extern struct pid init_struct_pid;  argument
77 struct pid *pidfd_pid(const struct file *file);
78 struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags);
80 int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret);
83 static inline struct pid *get_pid(struct pid *pid)  in get_pid()  argument
85 	if (pid)  in get_pid()
86 		refcount_inc(&pid->count);  in get_pid()
87 	return pid;  in get_pid()
90 extern void put_pid(struct pid *pid);
91 extern struct task_struct *pid_task(struct pid *pid, enum pid_type);
92 static inline bool pid_has_task(struct pid *pid, enum pid_type type)  in pid_has_task()  argument
94 	return !hlist_empty(&pid->tasks[type]);  in pid_has_task()
96 extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type);
98 extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
106 			struct pid *pid);
112  * look up a PID in the hash table. Must be called with the tasklist_lock
115  * find_pid_ns() finds the pid in the namespace specified
116  * find_vpid() finds the pid by its virtual id, i.e. in the current namespace
120 extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns);
121 extern struct pid *find_vpid(int nr);
124  * Lookup a PID in the hash table, and return with it's count elevated.
126 extern struct pid *find_get_pid(int nr);
127 extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
129 extern struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
131 extern void free_pid(struct pid *pid);
135  * ns_of_pid() returns the pid namespace in which the specified pid was
140  * 	an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid
141  * 	is expected to be non-NULL. If @pid is NULL, caller should handle
142  * 	the resulting NULL pid-ns.
144 static inline struct pid_namespace *ns_of_pid(struct pid *pid)  in ns_of_pid()  argument
147 	if (pid)  in ns_of_pid()
148 		ns = pid->numbers[pid->level].ns;  in ns_of_pid()
153  * is_child_reaper returns true if the pid is the init process
156  * with the pid number.
158 static inline bool is_child_reaper(struct pid *pid)  in is_child_reaper()  argument
160 	return pid->numbers[pid->level].nr == 1;  in is_child_reaper()
164  * the helpers to get the pid's id seen from different namespaces
167  * pid_vnr()   : virtual id, i.e. the id seen from the pid namespace of
174 static inline pid_t pid_nr(struct pid *pid)  in pid_nr()  argument
177 	if (pid)  in pid_nr()
178 		nr = pid->numbers[0].nr;  in pid_nr()
182 pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
183 pid_t pid_vnr(struct pid *pid);
185 #define do_each_pid_task(pid, type, task)				\  argument
187 		if ((pid) != NULL)					\
189 				&(pid)->tasks[type], pid_links[type]) {
193 			 * the same pid in the middle of de_thread().
195 #define while_each_pid_task(pid, type, task)				\  argument
201 #define do_each_pid_thread(pid, type, task)				\  argument
202 	do_each_pid_task(pid, type, task) {				\
206 #define while_each_pid_thread(pid, type, task)				\  argument
209 	} while_each_pid_task(pid, type, task)
211 static inline struct pid *task_pid(struct task_struct *task)  in task_pid()
221  * task_xid_vnr()    : virtual id, i.e. the id seen from the pid namespace of
225  * see also pid_nr() etc in include/linux/pid.h
231 	return tsk->pid;  in task_pid_nr()
298 	pid_t pid = 0;  in task_ppid_nr_ns()  local
302 		pid = task_tgid_nr_ns(rcu_dereference(tsk->real_parent), ns);  in task_ppid_nr_ns()
305 	return pid;  in task_ppid_nr_ns()