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
53 struct pid  struct
58 	/* lists of tasks that use this pid */  argument
67 extern struct pid init_struct_pid;  argument
73 extern struct pid *pidfd_pid(const struct file *file);
74 struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags);
76 int pidfd_create(struct pid *pid, unsigned int flags);
77 int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret);
79 static inline struct pid *get_pid(struct pid *pid)  in get_pid()  argument
81 	if (pid)  in get_pid()
82 		refcount_inc(&pid->count);  in get_pid()
83 	return pid;  in get_pid()
86 extern void put_pid(struct pid *pid);
87 extern struct task_struct *pid_task(struct pid *pid, enum pid_type);
88 static inline bool pid_has_task(struct pid *pid, enum pid_type type)  in pid_has_task()  argument
90 	return !hlist_empty(&pid->tasks[type]);  in pid_has_task()
92 extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type);
94 extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
102 			struct pid *pid);
111  * look up a PID in the hash table. Must be called with the tasklist_lock
114  * find_pid_ns() finds the pid in the namespace specified
115  * find_vpid() finds the pid by its virtual id, i.e. in the current namespace
119 extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns);
120 extern struct pid *find_vpid(int nr);
123  * Lookup a PID in the hash table, and return with it's count elevated.
125 extern struct pid *find_get_pid(int nr);
126 extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
128 extern struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
130 extern void free_pid(struct pid *pid);
134  * ns_of_pid() returns the pid namespace in which the specified pid was
139  * 	an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid
140  * 	is expected to be non-NULL. If @pid is NULL, caller should handle
141  * 	the resulting NULL pid-ns.
143 static inline struct pid_namespace *ns_of_pid(struct pid *pid)  in ns_of_pid()  argument
146 	if (pid)  in ns_of_pid()
147 		ns = pid->numbers[pid->level].ns;  in ns_of_pid()
152  * is_child_reaper returns true if the pid is the init process
155  * with the pid number.
157 static inline bool is_child_reaper(struct pid *pid)  in is_child_reaper()  argument
159 	return pid->numbers[pid->level].nr == 1;  in is_child_reaper()
163  * the helpers to get the pid's id seen from different namespaces
166  * pid_vnr()   : virtual id, i.e. the id seen from the pid namespace of
173 static inline pid_t pid_nr(struct pid *pid)  in pid_nr()  argument
176 	if (pid)  in pid_nr()
177 		nr = pid->numbers[0].nr;  in pid_nr()
181 pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
182 pid_t pid_vnr(struct pid *pid);
184 #define do_each_pid_task(pid, type, task)				\  argument
186 		if ((pid) != NULL)					\
188 				&(pid)->tasks[type], pid_links[type]) {
192 			 * the same pid in the middle of de_thread().
194 #define while_each_pid_task(pid, type, task)				\  argument
200 #define do_each_pid_thread(pid, type, task)				\  argument
201 	do_each_pid_task(pid, type, task) {				\
205 #define while_each_pid_thread(pid, type, task)				\  argument
208 	} while_each_pid_task(pid, type, task)
210 static inline struct pid *task_pid(struct task_struct *task)  in task_pid()
220  * task_xid_vnr()    : virtual id, i.e. the id seen from the pid namespace of
224  * see also pid_nr() etc in include/linux/pid.h
230 	return tsk->pid;  in task_pid_nr()
297 	pid_t pid = 0;  in task_ppid_nr_ns()  local
301 		pid = task_tgid_nr_ns(rcu_dereference(tsk->real_parent), ns);  in task_ppid_nr_ns()
304 	return pid;  in task_ppid_nr_ns()