makedev.3: New page for makedev(), major(), and minor() macros

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Reviewed-by: Phil Endecott <phil_vonar_endecott@chezphil.org>

diff --git a/man3/makedev.3 b/man3/makedev.3
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+.\" Copyright (c) 2008 Linux Foundation, written by Michael Kerrisk
+.\"     <mtk.manpages@gmail.com>
+.\"
+.\" Permission is granted to make and distribute verbatim copies of this
+.\" manual provided the copyright notice and this permission notice are
+.\" preserved on all copies.
+.\"
+.\" Permission is granted to copy and distribute modified versions of this
+.\" manual under the conditions for verbatim copying, provided that the
+.\" entire resulting derived work is distributed under the terms of a
+.\" permission notice identical to this one.
+.\"
+.\" Since the Linux kernel and libraries are constantly changing, this
+.\" manual page may be incorrect or out-of-date.  The author(s) assume no
+.\" responsibility for errors or omissions, or for damages resulting from
+.\" the use of the information contained herein.  The author(s) may not
+.\" have taken the same level of care in the production of this manual,
+.\" which is licensed free of charge, as they might when working
+.\" professionally.
+.\"
+.\" Formatted or processed versions of this manual, if unaccompanied by
+.\" the source, must acknowledge the copyright and authors of this work.
+.\"
+.TH MAKEDEV 3 2008-12-01 "Linux" "Linux Programmer's Manual"
+.SH NAME
+makedev, major, minor \- manage a device number
+.SH SYNOPSIS
+.nf
+.B #define _BSD_SOURCE
+.B #define <sys/types.h>
+
+.BI "dev_t makedev(int " maj ", int " min );
+
+.BI "int major(dev_t " dev );
+.BI "int minor(dev_t " dev );
+
+.fi
+.\" FIXME Add links
+.SH DESCRIPTION
+A device ID consists of two parts:
+a major ID, identifying the class of the device,
+and a minor ID, identifying a specific instance of a device in that class.
+A device ID is represented using the type
+.IR dev_t .
+
+Given major and minor device IDs,
+.BR makedev ()
+combines these to produce a device ID, returned as the function result.
+This device ID can be given to
+.BR mknod (2),
+for example.
+
+The
+.BR major ()
+and
+.BR minor ()
+functions perform the converse task: given a device ID,
+they return, respectively, the major and minor components.
+These macros can be useful to, for example,
+decompose the device IDs in the structure returned by
+.BR stat (2).
+.SH "CONFORMING TO"
+The
+.BR makedev ()
+.BR major ()
+and
+.BR minor ()
+functions are not specified in POSIX.1,
+but are present on many other systems.
+.\" The BSDs, HP-UX, Solaris, AIX, Irix
+.SH NOTES
+These interfaces are defined as macros.
+Since glibc 2.3.3,
+they have been aliases for three GNU-specific functions:
+.BR gnu_dev_makedev (3),
+.BR gnu_dev_major (3),
+and
+.BR gnu_dev_minor (3).
+The latter names are exported, but the traditional names are more portable.
+.SH "SEE ALSO"
+.BR mknod (2),
+.BR stat (2)
+.\" FIXME -- add SEE ALSO's from those pages.