DEVICE_PROBE man page on FreeBSD

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DEVICE_PROBE(9)		 BSD Kernel Developer's Manual	       DEVICE_PROBE(9)

     DEVICE_PROBE — probe for device existence

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

     DEVICE_PROBE(device_t dev);

     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 repre‐
     sented 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 allo‐
     cated during probe must be released and re-allocated if the attach method
     is called.	 In addition it is an absolute requirement that the probe rou‐
     tine 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 rou‐
     tine returns.  A driver may assume that the softc is preserved when it
     returns a success code of zero.

     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 indi‐
     cates 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.

			   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 sup‐
			   ports 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 gen‐
			   erally, with sepcialized drivers matching particu‐
			   lar types of serial ports that need special treat‐
			   ment 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 specifi‐
			   cally said to use this driver.


     This manual page was written by Doug Rabson.

BSD				 March 3, 2008				   BSD

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