DEVICE_PROBE -- probe for device existence
This device method should probe to see if the device is present. It
should return 0 if the device exists, ENXIO if it cannot be found. If
some other error happens during the probe (such as a memory allocation
failure), an appropriate error code should be returned. For cases where
more than one driver matches a device, a priority value can be returned.
In this case, success codes are values less than or equal to zero with
the highest value representing the best match. Failure codes are represented
by positive values and the regular UNIX error codes should be used
for the purpose.
If a driver returns a success code which is less than zero, it must not
assume that it will be the same driver which is attached to the device.
In particular, it must not assume that any values stored in the softc
structure will be available for its attach method and any resources allocated
during probe must be released and re-allocated if the attach method
is called. If a success code of zero is returned, the driver can assume
that it will be the one attached.
Devices which implement busses should use this method to probe for the
existence of devices attached to the bus and add them as children. If
this is combined with the use of bus_generic_attach(9) the child devices
will be automatically probed and attached.
A value equal to or less than zero indicates success, greater than zero
indicates an error (errno). For values equal to or less than zero: zero
indicates highest priority, no further probing is done; for a value less
than zero, the lower the value the lower the priority, e.g. -100 indicates
a lower priority than -50.
device(9), DEVICE_DETACH(9), DEVICE_IDENTIFY(9), DEVICE_SHUTDOWN(9)
This man page was written by Doug Rabson.
FreeBSD 5.2.1 June 16, 1998 FreeBSD 5.2.1 [ Back ]