.\" Copyright (c) 1998 Doug Rabson
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.\" $FreeBSD: src/share/man/man9/BUS_READ_IVAR.9,v 1.3.2.4 2001/12/17 11:30:18 ru Exp $
.\" $DragonFly: src/share/man/man9/BUS_READ_IVAR.9,v 1.3 2004/06/01 11:36:53 hmp Exp $
.\"
.Dd June 16, 1998
.Dt BUS_READ_IVAR 9
.Os
.Sh NAME
.Nm BUS_READ_IVAR ,
.Nm BUS_WRITE_IVAR
.Nd manipulate bus-specific device instance variables
.Sh SYNOPSIS
.In sys/param.h
.In sys/bus.h
.Ft int
.Fn BUS_READ_IVAR "device_t dev" "device_t child" "int index" "uintptr_t *result"
.Ft int
.Fn BUS_WRITE_IVAR "device_t dev" "device_t child" "int index" "uintptr_t value"
.Sh DESCRIPTION
These two methods manage a bus specific set of instance variables of
a child device.  The intention is that each different type of bus
defines a set of appropriate instance variables (such as ports and
irqs for ISA bus etc.)
.Pp
This information could be given to the child device as a struct but
that makes it hard for a bus to add or remove variables without
forcing an edit and recompile for all drivers which may not be
possible for vendor supplied binary drivers.
.Sh RETURN VALUES
Zero is returned on success, otherwise an appropriate error is returned.
.Sh SEE ALSO
.Xr device 9 ,
.Xr driver 9
.Sh AUTHORS
This man page was written by
.An Doug Rabson .