130 lines
4.1 KiB
Groff
130 lines
4.1 KiB
Groff
.\"
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.\" Copyright (c) 2002 M. Warner Losh
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.\" All rights reserved.
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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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