atomic_op.s

<B>Digital的Unix操作系统VAX 4.2源码</B>

/*	@(#)atomic_op.s	4.1     ULTRIX        7/3/90	*/
  
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 *   This software is  derived  from  software  received  from  the	*
 *   University    of   California,   Berkeley,   and   from   Bell	*
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/************************************************************************
 *
 *		Modification History
 *
 *
 ************************************************************************/

/*
 * int atomic_op (op, addr)
 * int op;
 * unsigned int addr;
 *
 * atomic_op returns 0 if atomic operation is performed successfully.
 * It returns a -1 if the operation wasn't performed because the lock
 * was already set.  Interlocked clear always succeeds.
 * 
 * If operation type is not a valid value, errno is set to EINVAL.
 * If operation is not performed because lock already set, errno is
 * set to EBUSY.
 */

#include "DEFS.h"
#define	KERNEL
#include <errno.h>
#include <sys/lock.h>
#undef	KERNEL

	.text

	.globl	_errno
	.globl	_atomic_op

_atomic_op:
	.word	0
	movl	4(ap),r0	# fetch operation code.
	movl	8(ap),r2	# fetch address.
	movl	$ATOMIC_LOCKBIT,r1 # bit 31 is soft lock.	
	
	cmpl	r0,$ATOMIC_CLEAR# check if valid operation code.
	bgtru   err_inval	# if not, go to error handler.

	bbs	$0,r0,clear	# if low bit clear, do clear operation.
	
set:	clrl	r0
	bbssi	r1,(r2),err_busy # interlocked set if not set.
	ret

clear:	bbcci	r1,(r2),1f	# interlocked clear.
1:	clrl	r0		# always succeed.
	ret

err_inval:
	movl	$-1,r0		# mark as failed.
	movl	$EINVAL,_errno  # Invalid command.
	ret
	
err_busy:
	movl	$-1,r0
	movl	$EBUSY,_errno   # Bit already set.
	ret