DEVICE(9)              FreeBSD Kernel Developer's Manual             DEVICE(9)

NAME
     device - an abstract representation of a device

SYNOPSIS
     typedef struct _device *device_t;

DESCRIPTION
     The device object represents a piece of hardware attached to the system
     such as an expansion card, the bus which that card is plugged into, disk
     drives attached to the expansion card etc.  The system defines one
     device, root_bus and all other devices are created dynamically during
     autoconfiguration.  Normally devices representing top-level buses in the
     system (ISA, PCI etc.) will be attached directly to root_bus and other
     devices will be added as children of their relevant bus.

     The devices in a system form a tree.  All devices except root_bus have a
     parent (see device_get_parent(9)).  In addition, any device can have
     children attached to it (see device_add_child(9),
     device_add_child_ordered(9), device_find_child(9),
     device_get_children(9), and device_delete_child(9)).

     A device which has been successfully probed and attached to the system
     will also have a driver (see device_get_driver(9) and driver(9)) and a
     devclass (see device_get_devclass(9) and devclass(9)).  Various other
     attributes of the device include a unit number (see device_get_unit(9)),
     verbose description (normally supplied by the driver, see
     device_set_desc(9) and device_get_desc(9)), a set of bus-specific
     variables (see device_get_ivars(9)) and a set of driver-specific
     variables (see device_get_softc(9)).

     Devices can be in one of several states:

     DS_NOTPRESENT  the device has not been probed for existence or the probe
                    failed

     DS_ALIVE       the device probe succeeded but not yet attached

     DS_ATTACHED    the device has been successfully attached

     DS_BUSY        the device is currently open

     The current state of the device can be determined by calling
     device_get_state(9).

SEE ALSO
     devclass(9), driver(9)

AUTHORS
     This manual page was written by Doug Rabson.

FreeBSD 13.1-RELEASE-p6        January 15, 2017        FreeBSD 13.1-RELEASE-p6