include/linux/rwsem-spinlock.h

   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 */