1 /* SPDX-License-Identifier: GPL-2.0 */ 2 /* rwsem-spinlock.h: fallback C implementation 3 * 4 * Copyright (c) 2001 David Howells (dhowells@redhat.com). 5 * - Derived partially from ideas by Andrea Arcangeli <andrea@suse.de> 6 * - Derived also from comments by Linus 7 */ 8 9 #ifndef _LINUX_RWSEM_SPINLOCK_H 10 #define _LINUX_RWSEM_SPINLOCK_H 11 12 #ifndef _LINUX_RWSEM_H 13 #error "please don't include linux/rwsem-spinlock.h directly, use linux/rwsem.h instead" 14 #endif 15 16 #ifdef __KERNEL__ 17 /* 18 * the rw-semaphore definition 19 * - if count is 0 then there are no active readers or writers 20 * - if count is +ve then that is the number of active readers 21 * - if count is -1 then there is one active writer 22 * - if wait_list is not empty, then there are processes waiting for the semaphore 23 */ 24 struct rw_semaphore { 25 __s32 count; 26 raw_spinlock_t wait_lock; 27 struct list_head wait_list; 28 #ifdef CONFIG_DEBUG_LOCK_ALLOC 29 struct lockdep_map dep_map; 30 #endif 31 }; 32 33 #define RWSEM_UNLOCKED_VALUE 0x00000000 34 35 extern void __down_read(struct rw_semaphore *sem); 36 extern int __must_check __down_read_killable(struct rw_semaphore *sem); 37 extern int __down_read_trylock(struct rw_semaphore *sem); 38 extern void __down_write(struct rw_semaphore *sem); 39 extern int __must_check __down_write_killable(struct rw_semaphore *sem); 40 extern int __down_write_trylock(struct rw_semaphore *sem); 41 extern void __up_read(struct rw_semaphore *sem); 42 extern void __up_write(struct rw_semaphore *sem); 43 extern void __downgrade_write(struct rw_semaphore *sem); 44 extern int rwsem_is_locked(struct rw_semaphore *sem); 45 46 #endif /* __KERNEL__ */ 47 #endif /* _LINUX_RWSEM_SPINLOCK_H */ 48