[mirror_ubuntu-bionic-kernel.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 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));

/*
 * 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 pid_next(task, type)					\
	((task)->pids[(type)].node.next)

#define pid_next_task(task, type) 				\
	hlist_entry(pid_next(task, type), struct task_struct,	\
			pids[(type)].node)


/* We could use hlist_for_each_entry_rcu here but it takes more arguments
 * than the do_each_task_pid/while_each_task_pid.  So we roll our own
 * to preserve the existing interface.
 */
#define do_each_task_pid(who, type, task)				\
	if ((task = find_task_by_pid_type(type, who))) {		\
		prefetch(pid_next(task, type));				\
		do {

#define while_each_task_pid(who, type, task)				\
		} while (pid_next(task, type) &&  ({			\
				task = pid_next_task(task, type);	\
				rcu_dereference(task);			\
				prefetch(pid_next(task, type));		\
				1; }) );				\
	}

#define do_each_pid_task(pid, type, task)				\
	if ((task = pid_task(pid, type))) {				\
		prefetch(pid_next(task, type));				\
		do {

#define while_each_pid_task(pid, type, task)				\
		} while (pid_next(task, type) &&  ({			\
				task = pid_next_task(task, type);	\
				rcu_dereference(task);			\
				prefetch(pid_next(task, type));		\
				1; }) );				\
	}

#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
	38	* resources, and since a new struct pid is allocated when the numeric
	39	* pid value is reused we don't mistakenly refer to new processes.
	40	*/
	41
1da177e4 LT	42	struct pid
1da177e4 LT	43	{
92476d7f	44	atomic_t count;
1da177e4 LT	45	/* Try to keep pid_chain in the same cacheline as nr for find_pid */
	46	int nr;
	47	struct hlist_node pid_chain;
92476d7f EB	48	/* lists of tasks that use this pid */
	49	struct hlist_head tasks[PIDTYPE_MAX];
	50	struct rcu_head rcu;
1da177e4 LT	51	};
1da177e4 LT	52
92476d7f EB	53	struct pid_link
	54	{
	55	struct hlist_node node;
	56	struct pid *pid;
	57	};
	58
	59	static inline struct pid get_pid(struct pid pid)
	60	{
	61	if (pid)
	62	atomic_inc(&pid->count);
	63	return pid;
	64	}
	65
	66	extern void FASTCALL(put_pid(struct pid *pid));
	67	extern struct task_struct FASTCALL(pid_task(struct pid pid, enum pid_type));
	68	extern struct task_struct FASTCALL(get_pid_task(struct pid pid,
	69	enum pid_type));
1da177e4 LT	70
	71	/*
	72	* attach_pid() and detach_pid() must be called with the tasklist_lock
	73	* write-held.
	74	*/
92476d7f EB	75	extern int FASTCALL(attach_pid(struct task_struct *task,
92476d7f EB	76	enum pid_type type, int nr));
1da177e4 LT	77
1da177e4 LT	78	extern void FASTCALL(detach_pid(struct task_struct *task, enum pid_type));
c18258c6 EB	79	extern void FASTCALL(transfer_pid(struct task_struct *old,
c18258c6 EB	80	struct task_struct *new, enum pid_type));
1da177e4 LT	81
	82	/*
	83	* look up a PID in the hash table. Must be called with the tasklist_lock
92476d7f EB	84	* or rcu_read_lock() held.
	85	*/
	86	extern struct pid *FASTCALL(find_pid(int nr));
	87
	88	/*
	89	* Lookup a PID in the hash table, and return with it's count elevated.
1da177e4	90	*/
92476d7f	91	extern struct pid *find_get_pid(int nr);
0804ef4b	92	extern struct pid *find_ge_pid(int nr);
1da177e4	93
92476d7f EB	94	extern struct pid *alloc_pid(void);
92476d7f EB	95	extern void FASTCALL(free_pid(struct pid *pid));
1da177e4	96
5feb8f5f EB	97	static inline pid_t pid_nr(struct pid *pid)
	98	{
	99	pid_t nr = 0;
	100	if (pid)
	101	nr = pid->nr;
	102	return nr;
	103	}
	104
92476d7f EB	105	#define pid_next(task, type) \
	106	((task)->pids[(type)].node.next)
	107
	108	#define pid_next_task(task, type) \
	109	hlist_entry(pid_next(task, type), struct task_struct, \
	110	pids[(type)].node)
	111
	112
	113	/* We could use hlist_for_each_entry_rcu here but it takes more arguments
	114	* than the do_each_task_pid/while_each_task_pid. So we roll our own
	115	* to preserve the existing interface.
	116	*/
1da177e4 LT	117	#define do_each_task_pid(who, type, task) \
1da177e4 LT	118	if ((task = find_task_by_pid_type(type, who))) { \
92476d7f	119	prefetch(pid_next(task, type)); \
1da177e4 LT	120	do {
	121
	122	#define while_each_task_pid(who, type, task) \
92476d7f EB	123	} while (pid_next(task, type) && ({ \
	124	task = pid_next_task(task, type); \
	125	rcu_dereference(task); \
	126	prefetch(pid_next(task, type)); \
	127	1; }) ); \
	128	}
1da177e4	129
558cb325 EB	130	#define do_each_pid_task(pid, type, task) \
	131	if ((task = pid_task(pid, type))) { \
	132	prefetch(pid_next(task, type)); \
	133	do {
	134
	135	#define while_each_pid_task(pid, type, task) \
	136	} while (pid_next(task, type) && ({ \
	137	task = pid_next_task(task, type); \
	138	rcu_dereference(task); \
	139	prefetch(pid_next(task, type)); \
	140	1; }) ); \
	141	}
	142
1da177e4	143	#endif /* _LINUX_PID_H */