Linux Cross Reference
Linux/include/asm-s390/semaphore.h

   /*
    *  include/asm-s390/semaphore.h
    *
    *  S390 version
    *    Copyright (C) 1999,2000 IBM Deutschland Entwicklung GmbH, IBM Corporation
    *
    *  Derived from "include/asm-i386/semaphore.h"
    *    (C) Copyright 1996 Linus Torvalds
    */
  
  #ifndef _S390_SEMAPHORE_H
  #define _S390_SEMAPHORE_H
  
  #include <asm/system.h>
  #include <asm/atomic.h>
  #include <linux/wait.h>
  
  struct semaphore {
          atomic_t count;
          int sleepers;
          wait_queue_head_t wait;
  };
  
  #define __SEM_DEBUG_INIT(name)
  
  #define __SEMAPHORE_INITIALIZER(name,count) \
  { ATOMIC_INIT(count), 0, __WAIT_QUEUE_HEAD_INITIALIZER((name).wait) \
          __SEM_DEBUG_INIT(name) }
  
  #define __MUTEX_INITIALIZER(name) \
          __SEMAPHORE_INITIALIZER(name,1)
  
  #define __DECLARE_SEMAPHORE_GENERIC(name,count) \
          struct semaphore name = __SEMAPHORE_INITIALIZER(name,count)
  
  #define DECLARE_MUTEX(name) __DECLARE_SEMAPHORE_GENERIC(name,1)
  #define DECLARE_MUTEX_LOCKED(name) __DECLARE_SEMAPHORE_GENERIC(name,0)
  
  extern inline void sema_init (struct semaphore *sem, int val)
  {
          *sem = (struct semaphore)__SEMAPHORE_INITIALIZER((*sem),val);
  }
  
  static inline void init_MUTEX (struct semaphore *sem)
  {
          sema_init(sem, 1);
  }
  
  static inline void init_MUTEX_LOCKED (struct semaphore *sem)
  {
          sema_init(sem, 0);
  }
  
  asmlinkage void __down_failed(void /* special register calling convention */);
  asmlinkage int  __down_failed_interruptible(void  /* params in registers */);
  asmlinkage int  __down_failed_trylock(void  /* params in registers */);
  asmlinkage void __up_wakeup(void /* special register calling convention */);
  
  asmlinkage void __down(struct semaphore * sem);
  asmlinkage int  __down_interruptible(struct semaphore * sem);
  asmlinkage int  __down_trylock(struct semaphore * sem);
  asmlinkage void __up(struct semaphore * sem);
  
  extern inline void down(struct semaphore * sem)
  {
          if (atomic_dec_return(&sem->count) < 0)
                  __down(sem);
  }
  
  extern inline int down_interruptible(struct semaphore * sem)
  {
          int ret = 0;
  
          if (atomic_dec_return(&sem->count) < 0)
                  ret = __down_interruptible(sem);
          return ret;
  }
  
  extern inline int down_trylock(struct semaphore * sem)
  {
          int ret = 0;
  
          if (atomic_dec_return(&sem->count) < 0)
                  ret = __down_trylock(sem);
          return ret;
  }
  
  extern inline void up(struct semaphore * sem)
  {
          if (atomic_inc_return(&sem->count) <= 0)
                  __up(sem);
  }
  
  /* rw mutexes (should that be mutices? =) -- throw rw
   * spinlocks and semaphores together, and this is what we
   * end up with...
   *
   * The lock is initialized to BIAS.  This way, a writer
   * subtracts BIAS ands gets 0 for the case of an uncontended
  * lock.  Readers decrement by 1 and see a positive value
  * when uncontended, negative if there are writers waiting
  * (in which case it goes to sleep).
  *
  * The value 0x01000000 supports up to 128 processors and
  * lots of processes.  BIAS must be chosen such that subl'ing
  * BIAS once per CPU will result in the long remaining
  * negative.
  *
  * In terms of fairness, this should result in the lock
  * flopping back and forth between readers and writers
  * under heavy use.
  *
  *              -ben
  */
 struct rw_semaphore {
         atomic_t                count;
         volatile unsigned int   write_bias_granted;
         volatile unsigned int   read_bias_granted;
         wait_queue_head_t       wait;
         wait_queue_head_t       write_bias_wait;
 };
 
 #define RW_LOCK_BIAS             0x01000000
 
 #define __RWSEM_DEBUG_INIT      /* */
 
 #define __RWSEM_INITIALIZER(name,count) \
 { ATOMIC_INIT(count), 0, 0, __WAIT_QUEUE_HEAD_INITIALIZER((name).wait), \
         __WAIT_QUEUE_HEAD_INITIALIZER((name).write_bias_wait) \
         __SEM_DEBUG_INIT(name) __RWSEM_DEBUG_INIT }
 
 #define __DECLARE_RWSEM_GENERIC(name,count) \
         struct rw_semaphore name = __RWSEM_INITIALIZER(name,count)
 
 #define DECLARE_RWSEM(name) __DECLARE_RWSEM_GENERIC(name,RW_LOCK_BIAS)
 #define DECLARE_RWSEM_READ_LOCKED(name) __DECLARE_RWSEM_GENERIC(name,RW_LOCK_BIAS-1)
 #define DECLARE_RWSEM_WRITE_LOCKED(name) __DECLARE_RWSEM_GENERIC(name,0)
 
 extern inline void init_rwsem(struct rw_semaphore *sem)
 {
         atomic_set(&sem->count, RW_LOCK_BIAS);
         sem->read_bias_granted = 0;
         sem->write_bias_granted = 0;
         init_waitqueue_head(&sem->wait);
         init_waitqueue_head(&sem->write_bias_wait);
 }
 
 extern void __down_read_failed(int, struct rw_semaphore *);
 extern void __down_write_failed(int, struct rw_semaphore *);
 extern void __rwsem_wake(int, struct rw_semaphore *);
 
 extern inline void down_read(struct rw_semaphore *sem)
 {
         int count;
         count = atomic_dec_return(&sem->count);
         if (count < 0)
                 __down_read_failed(count, sem);
 }
 
 extern inline void down_write(struct rw_semaphore *sem)
 {
         int count;
         count = atomic_add_return (-RW_LOCK_BIAS, &sem->count);
         if (count < 0)
                 __down_write_failed(count, sem);
 }
 
 /* When a reader does a release, the only significant
  * case is when there was a writer waiting, and we've
  * bumped the count to 0: we must wake the writer up.
  */
 extern inline void up_read(struct rw_semaphore *sem)
 {
         int count;
         count = atomic_inc_return(&sem->count);
         if (count == 0)
                 __rwsem_wake(count, sem);
 }
 
 /* releasing the writer is easy -- just release it and
  * wake up any sleepers.
  */
 extern inline void up_write(struct rw_semaphore *sem)
 {
         int count;
         count = atomic_add_return(RW_LOCK_BIAS, &sem->count);
         if (count >= 0 && count < RW_LOCK_BIAS)
                 __rwsem_wake(count, sem);
 }
 
 #endif