[deliverable/linux.git] / include / linux / pid.h

#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, 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));

/*
 * 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_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 */
Commit	Line	Data
1da177e4 LT	1	#ifndef _LINUX_PID_H
	2	#define _LINUX_PID_H
	3
92476d7f EB	4	#include <linux/rcupdate.h>
92476d7f EB	5
1da177e4 LT	6	enum pid_type
	7	{
	8	PIDTYPE_PID,
1da177e4 LT	9	PIDTYPE_PGID,
	10	PIDTYPE_SID,
	11	PIDTYPE_MAX
	12	};
	13
92476d7f EB	14	/*
	15	* What is struct pid?
	16	*
	17	* A struct pid is the kernel's internal notion of a process identifier.
	18	* It refers to individual tasks, process groups, and sessions. While
	19	* there are processes attached to it the struct pid lives in a hash
	20	* table, so it and then the processes that it refers to can be found
	21	* quickly from the numeric pid value. The attached processes may be
	22	* quickly accessed by following pointers from struct pid.
	23	*
	24	* Storing pid_t values in the kernel and refering to them later has a
	25	* problem. The process originally with that pid may have exited and the
	26	* pid allocator wrapped, and another process could have come along
	27	* and been assigned that pid.
	28	*
	29	* Referring to user space processes by holding a reference to struct
	30	* task_struct has a problem. When the user space process exits
	31	* the now useless task_struct is still kept. A task_struct plus a
	32	* stack consumes around 10K of low kernel memory. More precisely
	33	* this is THREAD_SIZE + sizeof(struct task_struct). By comparison
	34	* a struct pid is about 64 bytes.
	35	*
	36	* Holding a reference to struct pid solves both of these problems.
	37	* It is small so holding a reference does not consume a lot of
84d73786 SB	38	* resources, and since a new struct pid is allocated when the numeric pid
	39	* value is reused (when pids wrap around) we don't mistakenly refer to new
	40	* processes.
92476d7f EB	41	*/
92476d7f EB	42
1da177e4 LT	43	struct pid
1da177e4 LT	44	{
92476d7f	45	atomic_t count;
1da177e4 LT	46	/* Try to keep pid_chain in the same cacheline as nr for find_pid */
	47	int nr;
	48	struct hlist_node pid_chain;
92476d7f EB	49	/* lists of tasks that use this pid */
	50	struct hlist_head tasks[PIDTYPE_MAX];
	51	struct rcu_head rcu;
1da177e4 LT	52	};
1da177e4 LT	53
92476d7f EB	54	struct pid_link
	55	{
	56	struct hlist_node node;
	57	struct pid *pid;
	58	};
	59
	60	static inline struct pid get_pid(struct pid pid)
	61	{
	62	if (pid)
	63	atomic_inc(&pid->count);
	64	return pid;
	65	}
	66
	67	extern void FASTCALL(put_pid(struct pid *pid));
	68	extern struct task_struct FASTCALL(pid_task(struct pid pid, enum pid_type));
	69	extern struct task_struct FASTCALL(get_pid_task(struct pid pid,
	70	enum pid_type));
1da177e4	71
1a657f78 ON	72	extern struct pid get_task_pid(struct task_struct task, enum pid_type type);
1a657f78 ON	73
1da177e4 LT	74	/*
	75	* attach_pid() and detach_pid() must be called with the tasklist_lock
	76	* write-held.
	77	*/
92476d7f	78	extern int FASTCALL(attach_pid(struct task_struct *task,
e713d0da	79	enum pid_type type, struct pid *pid));
1da177e4	80	extern void FASTCALL(detach_pid(struct task_struct *task, enum pid_type));
c18258c6 EB	81	extern void FASTCALL(transfer_pid(struct task_struct *old,
c18258c6 EB	82	struct task_struct *new, enum pid_type));
1da177e4 LT	83
	84	/*
	85	* look up a PID in the hash table. Must be called with the tasklist_lock
92476d7f EB	86	* or rcu_read_lock() held.
	87	*/
	88	extern struct pid *FASTCALL(find_pid(int nr));
	89
	90	/*
	91	* Lookup a PID in the hash table, and return with it's count elevated.
1da177e4	92	*/
92476d7f	93	extern struct pid *find_get_pid(int nr);
0804ef4b	94	extern struct pid *find_ge_pid(int nr);
1da177e4	95
92476d7f EB	96	extern struct pid *alloc_pid(void);
92476d7f EB	97	extern void FASTCALL(free_pid(struct pid *pid));
1da177e4	98
5feb8f5f EB	99	static inline pid_t pid_nr(struct pid *pid)
	100	{
	101	pid_t nr = 0;
	102	if (pid)
	103	nr = pid->nr;
	104	return nr;
	105	}
	106
1d32849b AM	107	#define do_each_pid_task(pid, type, task) \
	108	do { \
	109	struct hlist_node *pos___; \
	110	if (pid != NULL) \
	111	hlist_for_each_entry_rcu((task), pos___, \
d387cae0 ON	112	&pid->tasks[type], pids[type].node) {
d387cae0 ON	113
1d32849b AM	114	#define while_each_pid_task(pid, type, task) \
1d32849b AM	115	} \
d387cae0	116	} while (0)
558cb325	117
1da177e4	118	#endif /* _LINUX_PID_H */