include/linux/rwsem-spinlock.h

   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 count is 0 then there are no active readers or writers
  19  * - if count is +ve then that is the number of active readers
  20  * - if count is -1 then there is one active writer
  21  * - if wait_list is not empty, then there are processes waiting for the semaphore
  22  */
  23 struct rw_semaphore {
  24         __s32                   count;
  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
  34 extern void __down_read(struct rw_semaphore *sem);
  35 extern int __down_read_trylock(struct rw_semaphore *sem);
  36 extern void __down_write(struct rw_semaphore *sem);
  37 extern void __down_write_nested(struct rw_semaphore *sem, int subclass);
  38 extern int __down_write_trylock(struct rw_semaphore *sem);
  39 extern void __up_read(struct rw_semaphore *sem);
  40 extern void __up_write(struct rw_semaphore *sem);
  41 extern void __downgrade_write(struct rw_semaphore *sem);
  42 extern int rwsem_is_locked(struct rw_semaphore *sem);
  43
  44 #endif /* __KERNEL__ */
  45 #endif /* _LINUX_RWSEM_SPINLOCK_H */