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
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).
devclass(9),
driver(9)
This manual page was written by
Doug
Rabson.