1e94ddb453
Remove some statements which are no longer correct after ino64, and clarify other. The rewording is not in fact specific to ino64 and improvements are useful on the stable branches. Noted and reviewed by: bde Sponsored by: The FreeBSD Foundation MFC after: 1 week
103 lines
3.0 KiB
Groff
103 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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.\" $FreeBSD$
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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 5
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