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 #include <linux/spinlock.h>
  16 #include <linux/list.h>
  17
  18 #ifdef __KERNEL__
  19
  20 #include <linux/types.h>
  21
  22 struct rwsem_waiter;
  23
  24 /*
  25  * the rw-semaphore definition
  26  * - if activity is 0 then there are no active readers or writers
  27  * - if activity is +ve then that is the number of active readers
  28  * - if activity is -1 then there is one active writer
  29  * - if wait_list is not empty, then there are processes waiting for the semaphore
  30  */
  31 struct rw_semaphore {
  32         __s32                   activity;
  33         spinlock_t              wait_lock;
  34         struct list_head        wait_list;
  35 #if RWSEM_DEBUG
  36         int                     debug;
  37 #endif
  38 };
  39
  40 /*
  41  * initialisation
  42  */
  43 #if RWSEM_DEBUG
  44 #define __RWSEM_DEBUG_INIT      , 0
  45 #else
  46 #define __RWSEM_DEBUG_INIT      /* */
  47 #endif
  48
  49 #define __RWSEM_INITIALIZER(name) \
  50 { 0, SPIN_LOCK_UNLOCKED, LIST_HEAD_INIT((name).wait_list) __RWSEM_DEBUG_INIT }
  51
  52 #define DECLARE_RWSEM(name) \
  53         struct rw_semaphore name = __RWSEM_INITIALIZER(name)
  54
  55 extern void FASTCALL(init_rwsem(struct rw_semaphore *sem));
  56 extern void FASTCALL(__down_read(struct rw_semaphore *sem));
  57 extern int FASTCALL(__down_read_trylock(struct rw_semaphore *sem));
  58 extern void FASTCALL(__down_write(struct rw_semaphore *sem));
  59 extern int FASTCALL(__down_write_trylock(struct rw_semaphore *sem));
  60 extern void FASTCALL(__up_read(struct rw_semaphore *sem));
  61 extern void FASTCALL(__up_write(struct rw_semaphore *sem));
  62 extern void FASTCALL(__downgrade_write(struct rw_semaphore *sem));
  63
  64 static inline int rwsem_is_locked(struct rw_semaphore *sem)
  65 {
  66         return (sem->activity != 0);
  67 }
  68
  69 #endif /* __KERNEL__ */
  70 #endif /* _LINUX_RWSEM_SPINLOCK_H */