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.\" Copyright (c) 1998 Doug Rabson
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.Dd April 19, 2022
.Dt DRIVER 9
.Os
.Sh NAME
.Nm driver
.Nd structure describing a device driver
.Sh SYNOPSIS
.Bd -literal
#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/bus.h>
#include <sys/module.h>

static int foo_probe(device_t);
static int foo_attach(device_t);
static int foo_detach(device_t);
static int foo_frob(device_t, int, int);
static int foo_twiddle(device_t, char *);

static device_method_t foo_methods[] = {
	/* Methods from the device interface */
	DEVMETHOD(device_probe,		foo_probe),
	DEVMETHOD(device_attach,	foo_attach),
	DEVMETHOD(device_detach,	foo_detach),

	/* Methods from the bogo interface */
	DEVMETHOD(bogo_frob,		foo_frob),
	DEVMETHOD(bogo_twiddle,		foo_twiddle),

	/* Terminate method list */
	DEVMETHOD_END
};

static driver_t foo_driver = {
	"foo",
	foo_methods,
	sizeof(struct foo_softc)
};

DRIVER_MODULE(foo, bogo, foo_driver, NULL, NULL);
.Ed
.Sh DESCRIPTION
Each driver in the kernel is described by a
.Dv driver_t
structure.
The structure contains the name of the device, a pointer
to a list of methods, an indication of the kind of device which the
driver implements and the size of the private data which the driver
needs to associate with a device instance.
Each driver will implement
one or more sets of methods (called interfaces).
The example driver
implements the standard "driver" interface and the fictitious "bogo"
interface.
.Pp
When a driver is registered with the system (by the
.Dv DRIVER_MODULE
macro, see
.Xr DRIVER_MODULE 9 ) ,
it is added to the list of drivers contained in the devclass
of its parent bus type.
For instance all PCI drivers would be
contained in the devclass named "pci" and all ISA drivers would be
in the devclass named "isa".
The reason the drivers are not held in the device object of the parent
bus is to handle multiple instances of a given type of bus.
The
.Dv DRIVER_MODULE
macro will also create the devclass with the name of the driver and
can optionally call extra initialisation code in the driver by
specifying an extra module event handler and argument as the last two
arguments.
.Sh SEE ALSO
.Xr devclass 9 ,
.Xr device 9 ,
.Xr DEVICE_ATTACH 9 ,
.Xr DEVICE_DETACH 9 ,
.Xr DEVICE_IDENTIFY 9 ,
.Xr DEVICE_PROBE 9 ,
.Xr DEVICE_SHUTDOWN 9 ,
.Xr DRIVER_MODULE 9
.Sh HISTORY
The
.Nm
framework first appeared in
.Fx 2.2.7 .
.Sh AUTHORS
This manual page was written by
.An Doug Rabson .