[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 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;
	unsigned 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 put_pid(struct pid *pid);
extern struct task_struct *pid_task(struct pid *pid, enum pid_type);
extern struct task_struct *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 void attach_pid(struct task_struct *task, enum pid_type type,
			struct pid *pid);
extern void detach_pid(struct task_struct *task, enum pid_type);
extern void change_pid(struct task_struct *task, enum pid_type,
			struct pid *pid);
extern void 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 *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 *);
int next_pidmap(struct pid_namespace *pid_ns, int last);

extern struct pid *alloc_pid(struct pid_namespace *ns);
extern void free_pid(struct pid *pid);

/*
 * 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 pid namespace of
 *               current.
 * 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);
pid_t pid_vnr(struct pid *pid);

#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) {

			/*
			 * Both old and new leaders may be attached to
			 * the same pid in the middle of de_thread().
			 */
#define while_each_pid_task(pid, type, task)				\
				if (type == PIDTYPE_PID)		\
					break;				\
			}						\
	} 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
4c3f2ead SB	43
	44	/*
	45	* struct upid is used to get the id of the struct pid, as it is
	46	* seen in particular namespace. Later the struct pid is found with
	47	* find_pid_ns() using the int nr and struct pid_namespace *ns.
	48	*/
	49
	50	struct upid {
	51	/* Try to keep pid_chain in the same cacheline as nr for find_pid */
	52	int nr;
	53	struct pid_namespace *ns;
	54	struct hlist_node pid_chain;
	55	};
	56
1da177e4 LT	57	struct pid
1da177e4 LT	58	{
92476d7f	59	atomic_t count;
92476d7f EB	60	/* lists of tasks that use this pid */
	61	struct hlist_head tasks[PIDTYPE_MAX];
	62	struct rcu_head rcu;
caafa432	63	unsigned int level;
4c3f2ead	64	struct upid numbers[1];
1da177e4 LT	65	};
1da177e4 LT	66
820e45db SB	67	extern struct pid init_struct_pid;
820e45db SB	68
92476d7f EB	69	struct pid_link
	70	{
	71	struct hlist_node node;
	72	struct pid *pid;
	73	};
	74
	75	static inline struct pid get_pid(struct pid pid)
	76	{
	77	if (pid)
	78	atomic_inc(&pid->count);
	79	return pid;
	80	}
	81
b3c97528 HH	82	extern void put_pid(struct pid *pid);
	83	extern struct task_struct pid_task(struct pid pid, enum pid_type);
	84	extern struct task_struct get_pid_task(struct pid pid, enum pid_type);
1da177e4	85
1a657f78 ON	86	extern struct pid get_task_pid(struct task_struct task, enum pid_type type);
1a657f78 ON	87
1da177e4 LT	88	/*
	89	* attach_pid() and detach_pid() must be called with the tasklist_lock
	90	* write-held.
	91	*/
24336eae ON	92	extern void attach_pid(struct task_struct *task, enum pid_type type,
24336eae ON	93	struct pid *pid);
b3c97528	94	extern void detach_pid(struct task_struct *task, enum pid_type);
24336eae ON	95	extern void change_pid(struct task_struct *task, enum pid_type,
24336eae ON	96	struct pid *pid);
b3c97528 HH	97	extern void transfer_pid(struct task_struct old, struct task_struct new,
b3c97528 HH	98	enum pid_type);
1da177e4	99
198fe21b PE	100	struct pid_namespace;
	101	extern struct pid_namespace init_pid_ns;
	102
1da177e4 LT	103	/*
1da177e4 LT	104	* look up a PID in the hash table. Must be called with the tasklist_lock
92476d7f	105	* or rcu_read_lock() held.
198fe21b PE	106	*
	107	* find_pid_ns() finds the pid in the namespace specified
	108	* find_pid() find the pid by its global id, i.e. in the init namespace
	109	* find_vpid() finr the pid by its virtual id, i.e. in the current namespace
	110	*
	111	* see also find_task_by_pid() set in include/linux/sched.h
92476d7f	112	*/
b3c97528	113	extern struct pid find_pid_ns(int nr, struct pid_namespace ns);
8990571e PE	114	extern struct pid *find_vpid(int nr);
8990571e PE	115	extern struct pid *find_pid(int nr);
92476d7f EB	116
	117	/*
	118	* Lookup a PID in the hash table, and return with it's count elevated.
1da177e4	119	*/
92476d7f	120	extern struct pid *find_get_pid(int nr);
198fe21b	121	extern struct pid find_ge_pid(int nr, struct pid_namespace );
74bd59bb	122	int next_pidmap(struct pid_namespace *pid_ns, int last);
1da177e4	123
8ef047aa	124	extern struct pid alloc_pid(struct pid_namespace ns);
b3c97528	125	extern void free_pid(struct pid *pid);
1da177e4	126
7af57294 PE	127	/*
	128	* the helpers to get the pid's id seen from different namespaces
	129	*
	130	* pid_nr() : global id, i.e. the id seen from the init namespace;
44c4e1b2 EB	131	* pid_vnr() : virtual id, i.e. the id seen from the pid namespace of
44c4e1b2 EB	132	* current.
7af57294 PE	133	* pid_nr_ns() : id seen from the ns specified.
	134	*
	135	* see also task_xid_nr() etc in include/linux/sched.h
	136	*/
	137
5feb8f5f EB	138	static inline pid_t pid_nr(struct pid *pid)
	139	{
	140	pid_t nr = 0;
	141	if (pid)
7af57294 PE	142	nr = pid->numbers[0].nr;
	143	return nr;
	144	}
	145
	146	pid_t pid_nr_ns(struct pid pid, struct pid_namespace ns);
44c4e1b2	147	pid_t pid_vnr(struct pid *pid);
5feb8f5f	148
1d32849b AM	149	#define do_each_pid_task(pid, type, task) \
	150	do { \
	151	struct hlist_node *pos___; \
	152	if (pid != NULL) \
	153	hlist_for_each_entry_rcu((task), pos___, \
d387cae0 ON	154	&pid->tasks[type], pids[type].node) {
d387cae0 ON	155
46f382d2 ON	156	/*
	157	* Both old and new leaders may be attached to
	158	* the same pid in the middle of de_thread().
	159	*/
1d32849b	160	#define while_each_pid_task(pid, type, task) \
46f382d2 ON	161	if (type == PIDTYPE_PID) \
46f382d2 ON	162	break; \
1d32849b	163	} \
d387cae0	164	} while (0)
558cb325	165
1da177e4	166	#endif /* _LINUX_PID_H */