#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 upid is used to get the id of the struct pid, as it is * seen in particular namespace. Later the struct pid is found with * find_pid_ns() using the int nr and struct pid_namespace *ns. */struct upid {	/* Try to keep pid_chain in the same cacheline as nr for find_pid */	int nr;	struct pid_namespace *ns;	struct hlist_node pid_chain;};struct pid{	atomic_t count;	/* lists of tasks that use this pid */	struct hlist_head tasks[PIDTYPE_MAX];	struct rcu_head rcu;	int level;	struct upid numbers[1];};extern struct pid init_struct_pid;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, struct pid *pid));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));struct pid_namespace;extern struct pid_namespace init_pid_ns;/* * look up a PID in the hash table. Must be called with the tasklist_lock * or rcu_read_lock() held. * * find_pid_ns() finds the pid in the namespace specified * find_pid() find the pid by its global id, i.e. in the init namespace * find_vpid() finr the pid by its virtual id, i.e. in the current namespace * * see also find_task_by_pid() set in include/linux/sched.h */extern struct pid *FASTCALL(find_pid_ns(int nr, struct pid_namespace *ns));extern struct pid *find_vpid(int nr);extern struct pid *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, struct pid_namespace *);extern struct pid *alloc_pid(struct pid_namespace *ns);extern void FASTCALL(free_pid(struct pid *pid));extern void zap_pid_ns_processes(struct pid_namespace *pid_ns);/* * the helpers to get the pid's id seen from different namespaces * * pid_nr()    : global id, i.e. the id seen from the init namespace; * pid_vnr()   : virtual id, i.e. the id seen from the namespace this pid *               belongs to. this only makes sence when called in the *               context of the task that belongs to the same namespace; * pid_nr_ns() : id seen from the ns specified. * * see also task_xid_nr() etc in include/linux/sched.h */static inline pid_t pid_nr(struct pid *pid){	pid_t nr = 0;	if (pid)		nr = pid->numbers[0].nr;	return nr;}pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);static inline pid_t pid_vnr(struct pid *pid){	pid_t nr = 0;	if (pid)		nr = pid->numbers[pid->level].nr;	return nr;}#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 */