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.\" $FreeBSD: src/share/man/man9/DEVICE_PROBE.9,v 1.4.2.6 2001/12/17 11:30:18 ru Exp $
.\" $DragonFly: src/share/man/man9/DEVICE_PROBE.9,v 1.5 2008/11/09 10:27:47 swildner Exp $
.\"
.Dd June 16, 1998
.Dt DEVICE_PROBE 9
.Os
.Sh NAME
.Nm DEVICE_PROBE
.Nd probe for device existence
.Sh SYNOPSIS
.In sys/param.h
.In sys/bus.h
.Ft int
.Fn DEVICE_PROBE "device_t dev"
.Sh DESCRIPTION
This device method should probe to see if the device is present.
It should return 0 if the device exists,
.Er 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.
.Pp
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.
.Pp
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
.Xr bus_generic_attach 9
the child devices will be automatically probed and attached.
.Sh RETURN VALUES
A value equal to or less than zero indicates success, greater than
zero indicates an error
.Va ( 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.
.Sh SEE ALSO
.Xr device 9 ,
.Xr DEVICE_ATTACH 9
.Sh AUTHORS
This man page was written by
.An Doug Rabson .