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