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DEVICE_PROBE - probe for device existence
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.
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
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
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.
device(9), DEVICE_ATTACH(9), DEVICE_DETACH(9), DEVICE_IDENTIFY(9),
This manual page was written by Doug Rabson.