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NAME

     DEVICE_PROBE - probe for device existence

SYNOPSIS

     #include <sys/param.h>
     #include <sys/bus.h>

     int
     DEVICE_PROBE(device_t dev);

DESCRIPTION

     The DEVICE_PROBE() 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.  In addition it is an absolute requirement that the
     probe routine have no side effects whatsoever.  The probe routine may be
     called more than once before the attach routine is called.

     If a success code of zero is returned, the driver can assume that it will
     be the one attached, but must not hold any resources when the probe
     routine returns.  A driver may assume that the softc is preserved when it
     returns a success code of zero.

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), DEVICE_DETACH(9), DEVICE_IDENTIFY(9),
     DEVICE_SHUTDOWN(9)

AUTHORS

     This manual page was written by Doug Rabson.