NAME¶
device_add_child
,
device_add_child_ordered
—
add a new device 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 arguments specify the name and unit
number of the device. If the name is unknown 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 instances (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 chance of
probing the device, the driver name should be specified 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
specified 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 specific 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 device 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, the
device_find_child(9) routine should be used to
ensure that the device has not already been added to the tree. Because the
device name and
devclass_t are associated 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 duplication of children devices.
Identify routines should use
BUS_ADD_CHILD(9)
instead of
device_add_child(9).
RETURN VALUES¶
The new device if successful, NULL otherwise.
SEE ALSO¶
BUS_ADD_CHILD(9),
device(9),
device_find_child(9),
DEVICE_IDENTIFY(9)
AUTHORS¶
This manual page was written by
Doug
Rabson.