man3/makedev.3

   1 .\" Copyright (c) 2008 Linux Foundation, written by Michael Kerrisk
   2 .\"     <mtk.manpages@gmail.com>
   3 .\"
   4 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   5 .\"
   6 .TH MAKEDEV 3 2021-03-22 "Linux man-pages (unreleased)" "Linux Programmer's Manual"
   7 .SH NAME
   8 makedev, major, minor \- manage a device number
   9 .SH LIBRARY
  10 Standard C library
  11 .RI ( libc ", " \-lc )
  12 .SH SYNOPSIS
  13 .nf
  14 .B #include <sys/sysmacros.h>
  15 .PP
  16 .BI "dev_t makedev(unsigned int " maj ", unsigned int " min );
  17 .PP
  18 .BI "unsigned int major(dev_t " dev );
  19 .BI "unsigned int minor(dev_t " dev );
  20 .fi
  21 .SH DESCRIPTION
  22 A device ID consists of two parts:
  23 a major ID, identifying the class of the device,
  24 and a minor ID, identifying a specific instance of a device in that class.
  25 A device ID is represented using the type
  26 .IR dev_t .
  27 .PP
  28 Given major and minor device IDs,
  29 .BR makedev ()
  30 combines these to produce a device ID, returned as the function result.
  31 This device ID can be given to
  32 .BR mknod (2),
  33 for example.
  34 .PP
  35 The
  36 .BR major ()
  37 and
  38 .BR minor ()
  39 functions perform the converse task: given a device ID,
  40 they return, respectively, the major and minor components.
  41 These macros can be useful to, for example,
  42 decompose the device IDs in the structure returned by
  43 .BR stat (2).
  44 .SH ATTRIBUTES
  45 For an explanation of the terms used in this section, see
  46 .BR attributes (7).
  47 .ad l
  48 .nh
  49 .TS
  50 allbox;
  51 lbx lb lb
  52 l l l.
  53 Interface       Attribute       Value
  54 T{
  55 .BR makedev (),
  56 .BR major (),
  57 .BR minor ()
  58 T}      Thread safety   MT-Safe
  59 .TE
  60 .hy
  61 .ad
  62 .sp 1
  63 .SH STANDARDS
  64 The
  65 .BR makedev (),
  66 .BR major (),
  67 and
  68 .BR minor ()
  69 functions are not specified in POSIX.1,
  70 but are present on many other systems.
  71 .\" The BSDs, HP-UX, Solaris, AIX, Irix.
  72 .\" The header location is inconsistent:
  73 .\" Could be sys/mkdev.h, sys/sysmacros.h, or sys/types.h.
  74 .SH NOTES
  75 These interfaces are defined as macros.
  76 Since glibc 2.3.3,
  77 they have been aliases for three GNU-specific functions:
  78 .BR gnu_dev_makedev (),
  79 .BR gnu_dev_major (),
  80 and
  81 .BR gnu_dev_minor ().
  82 The latter names are exported, but the traditional names are more portable.
  83 .PP
  84 The BSDs expose the definitions for these macros via
  85 .IR <sys/types.h> .
  86 Depending on the version,
  87 glibc also exposes definitions for these macros from that
  88 header file if suitable feature test macros are defined.
  89 However, this behavior was deprecated in glibc 2.25,
  90 .\" glibc commit dbab6577c6684c62bd2521c1c29dc25c3cac966f
  91 and since glibc 2.28,
  92 .\" glibc commit e16deca62e16f645213dffd4ecd1153c37765f17
  93 .I <sys/types.h>
  94 no longer provides these definitions.
  95 .SH SEE ALSO
  96 .BR mknod (2),
  97 .BR stat (2)