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DEVICE_ADD_CHILD(9) | Kernel Developer's Manual | DEVICE_ADD_CHILD(9) |
NAME¶
device_add_child, device_add_child_ordered — add a new device as a child of an existing deviceSYNOPSIS¶
#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 passNULL
. 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.September 12, 2006 | Debian |