path: root/include/linux/wait.h

#ifndef _LINUX_WAIT_H
#define _LINUX_WAIT_H
/*
 * Linux wait queue related types and methods
 */
#include <linux/list.h>
#include <linux/stddef.h>
#include <linux/spinlock.h>
#include <asm/current.h>
#include <uapi/linux/wait.h>

typedef struct __wait_queue wait_queue_t;
typedef int (*wait_queue_func_t)(wait_queue_t *wait, unsigned mode, int flags, void *key);
int default_wake_function(wait_queue_t *wait, unsigned mode, int flags, void *key);

/* __wait_queue::flags */
#define WQ_FLAG_EXCLUSIVE	0x01
#define WQ_FLAG_WOKEN		0x02

struct __wait_queue {
	unsigned int		flags;
	void			*private;
	wait_queue_func_t	func;
	struct list_head	task_list;
};

struct wait_bit_key {
	void			*flags;
	int			bit_nr;
#define WAIT_ATOMIC_T_BIT_NR	-1
	unsigned long		timeout;
};

struct wait_bit_queue {
	struct wait_bit_key	key;
	wait_queue_t		wait;
};

struct __wait_queue_head {
	spinlock_t		lock;
	struct list_head	task_list;
};
typedef struct __wait_queue_head wait_queue_head_t;

struct task_struct;

/*
 * Macros for declaration and initialisaton of the datatypes
 */

#define __WAITQUEUE_INITIALIZER(name, tsk) {				\
	.private	= tsk,						\
	.func		= default_wake_function,			\
	.task_list	= { NULL, NULL } }

#define DECLARE_WAITQUEUE(name, tsk)					\
	wait_queue_t name = __WAITQUEUE_INITIALIZER(name, tsk)

#define __WAIT_QUEUE_HEAD_INITIALIZER(name) {				\
	.lock		= __SPIN_LOCK_UNLOCKED(name.lock),		\
	.task_list	= { &(name).task_list, &(name).task_list } }

#define DECLARE_WAIT_QUEUE_HEAD(name) \
	wait_queue_head_t name = __WAIT_QUEUE_HEAD_INITIALIZER(name)

#define __WAIT_BIT_KEY_INITIALIZER(word, bit)				\
	{ .flags = word, .bit_nr = bit, }

#define __WAIT_ATOMIC_T_KEY_INITIALIZER(p)				\
	{ .flags = p, .bit_nr = WAIT_ATOMIC_T_BIT_NR, }

extern void __init_waitqueue_head(wait_queue_head_t *q, const char *name, struct lock_class_key *);

#define init_waitqueue_head(q)				\
	do {						\
		static struct lock_class_key __key;	\
							\
		__init_waitqueue_head((q), #q, &__key);	\
	} while (0)

#ifdef CONFIG_LOCKDEP
# define __WAIT_QUEUE_HEAD_INIT_ONSTACK(name) \
	({ init_waitqueue_head(&name); name; })
# define DECLARE_WAIT_QUEUE_HEAD_ONSTACK(name) \
	wait_queue_head_t name = __WAIT_QUEUE_HEAD_INIT_ONSTACK(name)
#else
# define DECLARE_WAIT_QUEUE_HEAD_ONSTACK(name) DECLARE_WAIT_QUEUE_HEAD(name)
#endif

static inline void init_waitqueue_entry(wait_queue_t *q, struct task_struct *p)
{
	q->flags	= 0;
	q->private	= p;
	q->func		= default_wake_function;
}

static inline void
init_waitqueue_func_entry(wait_queue_t *q, wait_queue_func_t func)
{
	q->flags	= 0;
	q->private	= NULL;
	q->func		= func;
}

/**
 * waitqueue_active -- locklessly test for waiters on the queue
 * @q: the waitqueue to test for waiters
 *
 * returns true if the wait list is not empty
 *
 * NOTE: this function is lockless and requires care, incorrect usage _will_
 * lead to sporadic and non-obvious failure.
 *
 * Use either while holding wait_queue_head_t::lock or when used for wakeups
 * with an extra smp_mb() like:
 *
 *      CPU0 - waker                    CPU1 - waiter
 *
 *                                      for (;;) {
 *      @cond = true;                     prepare_to_wait(&wq, &wait, state);
 *      smp_mb();                         // smp_mb() from set_current_state()
 *      if (waitqueue_active(wq))         if (@cond)
 *        wake_up(wq);                      break;
 *                                        schedule();
 *                                      }
 *                                      finish_wait(&wq, &wait);
 *
 * Because without the explicit smp_mb() it's possible for the
 * waitqueue_active() load to get hoisted over the @cond store such that we'll
 * observe an empty wait list while the waiter might not observe @cond.
 *
 * Also note that this 'optimization' trades a spin_lock() for an smp_mb(),
 * which (when the lock is uncontended) are of roughly equal cost.
 */
static inline int waitqueue_active(wait_queue_head_t *q)
{
	return !list_empty(&q->task_list);
}

/**
 * wq_has_sleeper - check if there are any waiting processes
 * @wq: wait queue head
 *
 * Returns true if wq has waiting processes
 *
 * Please refer to the comment for waitqueue_active.
 */
static inline bool wq_has_sleeper(wait_queue_head_t *wq)
{
	/*
	 * We need to be sure we are in sync with the
	 * add_wait_queue modifications to the wait queue.
	 *
	 * This memory barrier should be paired with one on the
	 * waiting side.
	 */
	smp_mb();
	return waitqueue_active(wq);
}

extern void add_wait_queue(wait_queue_head_t *q, wait_queue_t *wait);
extern void add_wait_queue_exclusive(wait_queue_head_t *q, wait_queue_t *wait);
extern void remove_wait_queue(wait_queue_head_t *q, wait_queue_t *wait);

static inline void __add_wait_queue(wait_queue_head_t *head, wait_queue_t *new)
{