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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.

     The following values are used by convention to indicate different
     strengths of matching in a probe routine.  Except as noted, these are
     just suggested values, and there's nothing magical about them.

     BUS_PROBE_SPECIFIC    The device that cannot be reprobed, and that no
                           possible other driver may exist (typically legacy
                           drivers who don't fallow all the rules, or special
                           needs drivers).

     BUS_PROBE_VENDOR      The device is supported by a vendor driver.  This
                           is for source or binary drivers that are not yet
                           integrated into the FreeBSD tree.  Its use in the
                           base OS is prohibited.

     BUS_PROBE_DEFAULT     The device is a normal device matching some plug
                           and play ID.  This is the normal return value for
                           drivers to use.  It is intended that nearly all of
                           the drivers in the tree should return this value.

     BUS_PROBE_LOW_PRIORITY
                           The driver is a legacy driver, or an otherwise less
                           desirable driver for a given plug and play ID.  The
                           driver has special requirements like when there are
                           two drivers that support overlapping series of
                           hardware devices.  In this case the one that
                           supports the older part of the line would return
                           this value, while the one that supports the newer
                           ones would return BUS_PROBE_DEFAULT.

     BUS_PROBE_GENERIC     The driver matches the type of device generally.
                           This allows drivers to match all serial ports
                           generally, with sepcialized drivers matching
                           particular types of serial ports that need special
                           treatment for some reason.

     BUS_PROBE_HOOVER      The driver matches all unclaimed devices on a bus.
                           The ugen(5) device is one example.

     BUS_PROBE_NOWILDCARD  The driver expects its parent to tell it which
                           children to manage and no probing is really done.
                           The device only matches if its parent bus
                           specifically said to use this driver.

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.