DEVICE_PROBE(9)

NAME
DEVICE_PROBE - probe for device existence

SYNOPSIS
#include <sys/param.h>
#include <sys/bus.h>
int
DEVICE_PROBE(device_t dev);

DESCRIPTION
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.

RETURN VALUES
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.

SEE ALSO
device(9), DEVICE_ATTACH(9)

AUTHORS
This man page was written by Doug Rabson.