man3/makedev.3

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  26 .TH MAKEDEV 3 2017-09-15 "Linux" "Linux Programmer's Manual"
  27 .SH NAME
  28 makedev, major, minor \- manage a device number
  29 .SH SYNOPSIS
  30 .nf
  31 .B #include <sys/sysmacros.h>
  32 .PP
  33 .BI "dev_t makedev(unsigned int " maj ", unsigned int " min );
  34 .PP
  35 .BI "unsigned int major(dev_t " dev );
  36 .BI "unsigned int minor(dev_t " dev );
  37 .fi
  38 .SH DESCRIPTION
  39 A device ID consists of two parts:
  40 a major ID, identifying the class of the device,
  41 and a minor ID, identifying a specific instance of a device in that class.
  42 A device ID is represented using the type
  43 .IR dev_t .
  44 .PP
  45 Given major and minor device IDs,
  46 .BR makedev ()
  47 combines these to produce a device ID, returned as the function result.
  48 This device ID can be given to
  49 .BR mknod (2),
  50 for example.
  51 .PP
  52 The
  53 .BR major ()
  54 and
  55 .BR minor ()
  56 functions perform the converse task: given a device ID,
  57 they return, respectively, the major and minor components.
  58 These macros can be useful to, for example,
  59 decompose the device IDs in the structure returned by
  60 .BR stat (2).
  61 .SH ATTRIBUTES
  62 For an explanation of the terms used in this section, see
  63 .BR attributes (7).
  64 .TS
  65 allbox;
  66 lbw27 lb lb
  67 l l l.
  68 Interface       Attribute       Value
  69 T{
  70 .BR makedev (),
  71 .BR major (),
  72 .BR minor ()
  73 T}      Thread safety   MT-Safe
  74 .TE
  75 .SH CONFORMING TO
  76 The
  77 .BR makedev (),
  78 .BR major (),
  79 and
  80 .BR minor ()
  81 functions are not specified in POSIX.1,
  82 but are present on many other systems.
  83 .\" The BSDs, HP-UX, Solaris, AIX, Irix.
  84 .\" The header location is inconsistent:
  85 .\" Could be sys/mkdev.h, sys/sysmacros.h, or sys/types.h.
  86 .SH NOTES
  87 These interfaces are defined as macros.
  88 Since glibc 2.3.3,
  89 they have been aliases for three GNU-specific functions:
  90 .BR gnu_dev_makedev (),
  91 .BR gnu_dev_major (),
  92 and
  93 .BR gnu_dev_minor ().
  94 The latter names are exported, but the traditional names are more portable.
  95 .PP
  96 The BSDs expose the definitions for these macros via
  97 .IR <sys/types.h> .
  98 glibc also exposes definitions for these macros from that
  99 header file if suitable feature test macros are defined,
 100 but this is deprecated and will be removed in the future.
 101 .SH SEE ALSO
 102 .BR mknod (2),
 103 .BR stat (2)