19  * What is struct pid?
21  * A struct pid is the kernel's internal notion of a process identifier.
23  * there are processes attached to it the struct pid lives in a hash
25  * quickly from the numeric pid value.  The attached processes may be
26  * quickly accessed by following pointers from struct pid.
29  * problem.  The process originally with that pid may have exited and the
30  * pid allocator wrapped, and another process could have come along
31  * and been assigned that pid.
38  * a struct pid is about 64 bytes.
40  * Holding a reference to struct pid solves both of these problems.
42  * resources, and since a new struct pid is allocated when the numeric pid
49  * struct upid is used to get the id of the struct pid, as it is
50  * seen in particular namespace. Later the struct pid is found with
59 struct pid  struct
64 	/* lists of tasks that use this pid */  argument
73 extern struct pid init_struct_pid;  argument
79 extern struct pid *pidfd_pid(const struct file *file);
80 struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags);
81 int pidfd_create(struct pid *pid, unsigned int flags);
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);
118  * look up a PID in the hash table. Must be called with the tasklist_lock
121  * find_pid_ns() finds the pid in the namespace specified
122  * find_vpid() finds the pid by its virtual id, i.e. in the current namespace
126 extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns);
127 extern struct pid *find_vpid(int nr);
130  * Lookup a PID in the hash table, and return with it's count elevated.
132 extern struct pid *find_get_pid(int nr);
133 extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
135 extern struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
137 extern void free_pid(struct pid *pid);
141  * ns_of_pid() returns the pid namespace in which the specified pid was
146  * 	an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid
147  * 	is expected to be non-NULL. If @pid is NULL, caller should handle
148  * 	the resulting NULL pid-ns.
150 static inline struct pid_namespace *ns_of_pid(struct pid *pid)  in ns_of_pid()  argument
153 	if (pid)  in ns_of_pid()
154 		ns = pid->numbers[pid->level].ns;  in ns_of_pid()
159  * is_child_reaper returns true if the pid is the init process
162  * with the pid number.
164 static inline bool is_child_reaper(struct pid *pid)  in is_child_reaper()  argument
166 	return pid->numbers[pid->level].nr == 1;  in is_child_reaper()
170  * the helpers to get the pid's id seen from different namespaces
173  * pid_vnr()   : virtual id, i.e. the id seen from the pid namespace of
180 static inline pid_t pid_nr(struct pid *pid)  in pid_nr()  argument
183 	if (pid)  in pid_nr()
184 		nr = pid->numbers[0].nr;  in pid_nr()
188 pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
189 pid_t pid_vnr(struct pid *pid);
191 #define do_each_pid_task(pid, type, task)				\  argument
193 		if ((pid) != NULL)					\
195 				&(pid)->tasks[type], pid_links[type]) {
199 			 * the same pid in the middle of de_thread().
201 #define while_each_pid_task(pid, type, task)				\  argument
207 #define do_each_pid_thread(pid, type, task)				\  argument
208 	do_each_pid_task(pid, type, task) {				\
212 #define while_each_pid_thread(pid, type, task)				\  argument
215 	} while_each_pid_task(pid, type, task)