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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.
      The new device if successful, NULL otherwise.
      device(9)

AUTHORS

      This manual page was written by Doug Rabson.