device -- an abstract representation of a device
typedef struct device *device_t;
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 busses 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).
devclass(9), driver(9)
This man page was written by Doug Rabson.
FreeBSD 5.2.1 June 16, 1998 FreeBSD 5.2.1 [ Back ] |
