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DEVICE_ADD_CHILD(9)	 BSD 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 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 appro‐
     priate 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-config‐
     ured unit number), that unit should be passed.  If the specified unit
     number is already allocated, a new unit will be allocated and a diagnos‐
     tic 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 order‐
     ing.  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), previ‐
     ous 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.

BSD			      September 12, 2006			   BSD
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