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 change of probing the device, the driver name should 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, 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 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 chil-
     dren devices.

RETURN VALUES

     The new device if successful, NULL otherwise.

SEE ALSO

     device(9)

AUTHORS

     This manual page was written by Doug Rabson.