#ifndef _LINUX_PID_H#define _LINUX_PID_H#include <linux/rcupdate.h>enum pid_type{	PIDTYPE_PID,	PIDTYPE_PGID,	PIDTYPE_SID,	PIDTYPE_MAX};/* * What is struct pid? * * A struct pid is the kernel's internal notion of a process identifier. * It refers to individual tasks, process groups, and sessions.  While * there are processes attached to it the struct pid lives in a hash * table, so it and then the processes that it refers to can be found * quickly from the numeric pid value.  The attached processes may be * quickly accessed by following pointers from struct pid. * * Storing pid_t values in the kernel and refering to them later has a * problem.  The process originally with that pid may have exited and the * pid allocator wrapped, and another process could have come along * and been assigned that pid. * * Referring to user space processes by holding a reference to struct * task_struct has a problem.  When the user space process exits * the now useless task_struct is still kept.  A task_struct plus a * stack consumes around 10K of low kernel memory.  More precisely * this is THREAD_SIZE + sizeof(struct task_struct).  By comparison * a struct pid is about 64 bytes. * * Holding a reference to struct pid solves both of these problems. * It is small so holding a reference does not consume a lot of * resources, and since a new struct pid is allocated when the numeric pid * value is reused (when pids wrap around) we don't mistakenly refer to new * processes. */struct pid{	atomic_t count;	/* Try to keep pid_chain in the same cacheline as nr for find_pid */	int nr;	struct hlist_node pid_chain;	/* lists of tasks that use this pid */	struct hlist_head tasks[PIDTYPE_MAX];	struct rcu_head rcu;};struct pid_link{	struct hlist_node node;	struct pid *pid;};static inline struct pid *get_pid(struct pid *pid){	if (pid)		atomic_inc(&pid->count);	return pid;}extern void FASTCALL(put_pid(struct pid *pid));extern struct task_struct *FASTCALL(pid_task(struct pid *pid, enum pid_type));extern struct task_struct *FASTCALL(get_pid_task(struct pid *pid,						enum pid_type));extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);/* * attach_pid() and detach_pid() must be called with the tasklist_lock * write-held. */extern int FASTCALL(attach_pid(struct task_struct *task,				enum pid_type type, int nr));extern void FASTCALL(detach_pid(struct task_struct *task, enum pid_type));extern void FASTCALL(transfer_pid(struct task_struct *old,				  struct task_struct *new, enum pid_type));/* * look up a PID in the hash table. Must be called with the tasklist_lock * or rcu_read_lock() held. */extern struct pid *FASTCALL(find_pid(int nr));/* * Lookup a PID in the hash table, and return with it's count elevated. */extern struct pid *find_get_pid(int nr);extern struct pid *find_ge_pid(int nr);extern struct pid *alloc_pid(void);extern void FASTCALL(free_pid(struct pid *pid));static inline pid_t pid_nr(struct pid *pid){	pid_t nr = 0;	if (pid)		nr = pid->nr;	return nr;}#define do_each_task_pid(who, type, task)				\	do {								\		struct hlist_node *pos___;				\		struct pid *pid___ = find_pid(who);			\		if (pid___ != NULL)					\			hlist_for_each_entry_rcu((task), pos___,	\				&pid___->tasks[type], pids[type].node) {#define while_each_task_pid(who, type, task)				\			}						\	} while (0)#define do_each_pid_task(pid, type, task)				\	do {								\		struct hlist_node *pos___;				\		if (pid != NULL)					\			hlist_for_each_entry_rcu((task), pos___,	\				&pid->tasks[type], pids[type].node) {#define while_each_pid_task(pid, type, task)				\			}						\	} while (0)#endif /* _LINUX_PID_H */