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101 lines
3.0 KiB
Groff
101 lines
3.0 KiB
Groff
.\" Copyright (c) 2008 Ed Schouten <ed@FreeBSD.org>
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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. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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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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.Dd August 3, 2017
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.Dt MAKEDEV 3
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.Os
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.Sh NAME
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.Nm makedev ,
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.Nm major ,
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.Nm minor
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.Nd device number conversion
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.Sh SYNOPSIS
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.In sys/types.h
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.Ft dev_t
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.Fn makedev "int major" "int minor"
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.Ft int
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.Fn major "dev_t dev"
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.Ft int
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.Fn minor "dev_t dev"
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.Sh DESCRIPTION
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The
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.Fn makedev
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macro returns a device number created from the provided
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.Fa major
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and
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.Fa minor
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number.
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The
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.Fn major
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and
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.Fn minor
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macros return the original numbers from the device number
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.Fa dev .
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In other words, for a value
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.Va dev
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of the type
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.Vt dev_t ,
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and values
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.Va ma , mi
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of the type
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.Vt int ,
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the assertions
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.Dl dev == makedev(major(dev), minor(dev))
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.Dl ma == major(makedev(ma, mi))
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.Dl mi == minor(makedev(ma, mi))
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are valid.
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.Pp
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In previous implementations of
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.Fx
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all block and character devices were uniquely identified by a pair of
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stable major and minor numbers.
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The major number referred to a certain device class (e.g. disks, TTYs)
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while the minor number identified an instance within the device class.
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Later versions of
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.Fx
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automatically generate a unique device number for each character device
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visible in
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.Pa /dev/ .
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These numbers are not divided in device classes and are not guaranteed
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to be stable upon reboot or driver reload.
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.Pp
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On
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.Fx
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these macros are only used by utilities that need to exchange numbers
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with other operating systems that may use different encodings for
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.Vt dev_t ,
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but also applications that present these numbers to the user in a more
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conventional way.
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.Sh RETURN VALUES
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The
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.Fn major
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and
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.Fn minor
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macros return numbers whose value can span the complete range of an
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.Vt int .
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.Sh SEE ALSO
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.Xr mknod 2 ,
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.Xr devname 3 ,
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.Xr devfs 4
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