include/linux/rwsem-spinlock.h

/* SPDX-License-Identifier: GPL-2.0 */
/* rwsem-spinlock.h: fallback C implementation
 *
 * Copyright (c) 2001   David Howells (dhowells@redhat.com).
 * - Derived partially from ideas by Andrea Arcangeli <andrea@suse.de>
 * - Derived also from comments by Linus
 */

#ifndef _LINUX_RWSEM_SPINLOCK_H
#define _LINUX_RWSEM_SPINLOCK_H

#ifndef _LINUX_RWSEM_H
#error "please don't include linux/rwsem-spinlock.h directly, use linux/rwsem.h instead"
#endif

#ifdef __KERNEL__
/*
 * the rw-semaphore definition
 * - if count is 0 then there are no active readers or writers
 * - if count is +ve then that is the number of active readers
 * - if count is -1 then there is one active writer
 * - if wait_list is not empty, then there are processes waiting for the semaphore
 */
struct rw_semaphore {
	__s32			count;
	raw_spinlock_t		wait_lock;
	struct list_head	wait_list;
#ifdef CONFIG_DEBUG_LOCK_ALLOC
	struct lockdep_map dep_map;
#endif
};

#define RWSEM_UNLOCKED_VALUE		0x00000000

extern void __down_read(struct rw_semaphore *sem);
extern int __must_check __down_read_killable(struct rw_semaphore *sem);
extern int __down_read_trylock(struct rw_semaphore *sem);
extern void __down_write(struct rw_semaphore *sem);
extern int __must_check __down_write_killable(struct rw_semaphore *sem);
extern int __down_write_trylock(struct rw_semaphore *sem);
extern void __up_read(struct rw_semaphore *sem);
extern void __up_write(struct rw_semaphore *sem);
extern void __downgrade_write(struct rw_semaphore *sem);
extern int rwsem_is_locked(struct rw_semaphore *sem);

#endif /* __KERNEL__ */
#endif /* _LINUX_RWSEM_SPINLOCK_H */