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NAME

     BUS_READ_IVAR, BUS_WRITE_IVAR - manipulate bus-specific device instance
     variables

SYNOPSIS

     #include <sys/param.h>
     #include <sys/bus.h>

     int
     BUS_READ_IVAR(device_t dev, device_t child, int index,
             uintptr_t *result);

     int
     BUS_WRITE_IVAR(device_t dev, device_t child, int index, uintptr_t value);

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.)

     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.

RETURN VALUES

     Zero is returned on success, otherwise an appropriate error is returned.

SEE ALSO

     device(9), driver(9)

AUTHORS

     This manual page was written by Doug Rabson.