a476ba06d5
o Remove All Rights Reserved from my notices o imp@FreeBSD.org everywhere o regularize punctiation, eliminate date ranges o Make sure that it's clear that I don't claim All Rights reserved by listing All Rights Reserved on same line as other copyright holders (but not me). Other such holders are also listed last where it's clear.
129 lines
4.1 KiB
Groff
129 lines
4.1 KiB
Groff
.\"
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.\" Copyright (c) 2002 M. Warner Losh <imp@FreeBSD.org>
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd March 26, 2014
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.Dt DEVCTL 4
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.Os
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.Sh NAME
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.Nm devctl
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.Nd "device event reporting and device control interface"
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.Sh DESCRIPTION
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The
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.Nm
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device is used to report device events from the kernel.
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Future versions will allow for some device control as well.
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.Sh IMPLEMENTATION NOTES
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This design allows only one reader for
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.Pa /dev/devctl .
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This is not desirable
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in the long run, but will get a lot of hair out of this implementation.
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Maybe we should make this device a clonable device.
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.Pp
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Also note: we specifically do not attach a device to the
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.Vt device_t
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tree
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to avoid potential chicken and egg problems.
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One could argue that all of this belongs to the root node.
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One could also further argue that the
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.Xr sysctl 3
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interface that we have now might more properly be an
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.Xr ioctl 2
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interface.
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.Pp
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.Dv SIGIO
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support is included in the driver.
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However, the author is not sure that the
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.Dv SIGIO
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support is done correctly.
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It was copied from a driver that had
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.Dv SIGIO
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support that likely has not been
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tested since
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.Fx 3.4
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or
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.Fx 2.2.8 !
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.Pp
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The read channel for this device is used to report changes to
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userland in realtime.
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We return one record at a time.
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If you try to read this device a character at a time, you will lose
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the rest of the data.
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Listening programs are expected to cope.
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.Pp
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The sysctl
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.Va hw.bus.devctl_queue
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can be used to control queue length.
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It is set to 0 to disable
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.Nm
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when no
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.Xr devd 8
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is running.
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.Sh PROTOCOL
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The
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.Nm
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device
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uses an
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.Tn ASCII
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protocol.
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The driver returns one record at a time to its readers.
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Each record is terminated with a newline.
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The first character of the record is the event type.
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.Pp
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.Bl -column -compact "Type" "Description"
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.Em "Type Description"
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! A notify event, such as a link state change.
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+ Device node in tree attached.
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- Device node in tree detached.
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? Unknown device detected.
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.El
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.Ss Message Formats
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Except for the first character in the record, attach and detach
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messages have the same format.
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.Pp
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.D1 Ar T Ns Ar dev Li at Ar parent Li on Ar location
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.Pp
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.Bl -column -compact "location" "Description"
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.Em "Part Description"
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.It Ar T Ta "+ or -"
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.It Ar dev Ta "The device name that was attached/detached."
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.It Ar parent Ta "The device name of the parent bus that attached the device."
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.It Ar location Ta "Bus specific location information."
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.El
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.Pp
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The nomatch messages can be used to load devices driver.
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If you load a device driver, then one of two things can happen.
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If the device driver attaches to something, you will get a device
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attached message.
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If it does not, then nothing will happen.
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.Pp
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The attach and detach messages arrive after the event.
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This means one cannot use the attach message to load an alternate
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driver.
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The attach message driver has already claimed this device.
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One cannot use the detach messages to flush data to the device.
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The device is already gone.
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.Sh SEE ALSO
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.Xr devd 8
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