device_add_child(9)

NAME

device_add_child, device_add_child_ordered - add a new de

vice as a child
of an existing device

SYNOPSIS

#include <sys/param.h>
#include <sys/bus.h>
device_t
device_add_child(device_t dev, const char *name, int unit);
device_t
device_add_child_ordered(device_t dev, int order, const char
*name,
        int unit);

DESCRIPTION

Create a new child device of dev. The name and unit argu

ments specify
the name and unit number of the device. If the name is un

known then the
caller should pass NULL. If the unit is unknown then the

caller should
pass -1 and the system will choose the next available unit

number.

The name of the device is used to determine which drivers

might be appropriate for the device. If a name is specified then only

drivers of that
name are probed. If no name is given then all drivers for

the owning bus
are probed. In any event, only the name of the device is

stored so that
one may safely unload/load a driver bound to that name.

This allows busses which can uniquely identify device in

stances (such as
PCI) to allow each driver to check each device instance for

a match. For
busses which rely on supplied probe hints where only one

driver can have
a change of probing the device, the driver name should spec

ified as the
device name.

Normally unit numbers will be chosen automatically by the

system and a
unit number of -1 should be given. When a specific unit

number is
desired (e.g. for wiring a particular piece of hardware to a

pre-configured unit number), that unit should be passed. If the spec

ified unit
number is already allocated, a new unit will be allocated

and a diagnostic message printed.

If the devices attached to a bus must be probed in a specif

ic order (e.g.
for the ISA bus some devices are sensitive to failed probe

attempts of
unrelated drivers and therefore must be probed first), the

order argument
of device_add_child_ordered() should be used to specify a

partial ordering. The new device will be added before any existing de

vice with a
greater order. If device_add_child() is used, then the new

child will be
added as if its order was zero.

When adding a device in the context of DEVICE_IDENTIFY(9)

routine, some
care must be taken to ensure that the device has not already

been added
to the tree. Because the device name and devclass_t are as

sociated at
probe time (not child addition time), previous instances of

the driver
(say in a module that was later unloaded) may have already

added the
instance. Authors of bus drivers must likewise be careful

when adding
children when they are loaded and unloaded to avoid duplica

tion of children devices.

RETURN VALUES

The new device if successful, NULL otherwise.

SEE ALSO

device(9)

AUTHORS

This manual page was written by Doug Rabson.

BSD May 13, 2004

BSD