vendor/golang.org/x/sys/unix/dev_linux.go

   1 // Copyright 2017 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 // Functions to access/create device major and minor numbers matching the
   6 // encoding used by the Linux kernel and glibc.
   7 //
   8 // The information below is extracted and adapted from bits/sysmacros.h in the
   9 // glibc sources:
  10 //
  11 // dev_t in glibc is 64-bit, with 32-bit major and minor numbers. glibc's
  12 // default encoding is MMMM Mmmm mmmM MMmm, where M is a hex digit of the major
  13 // number and m is a hex digit of the minor number. This is backward compatible
  14 // with legacy systems where dev_t is 16 bits wide, encoded as MMmm. It is also
  15 // backward compatible with the Linux kernel, which for some architectures uses
  16 // 32-bit dev_t, encoded as mmmM MMmm.
  17
  18 package unix
  19
  20 // Major returns the major component of a Linux device number.
  21 func Major(dev uint64) uint32 {
  22         major := uint32((dev & 0x00000000000fff00) >> 8)
  23         major |= uint32((dev & 0xfffff00000000000) >> 32)
  24         return major
  25 }
  26
  27 // Minor returns the minor component of a Linux device number.
  28 func Minor(dev uint64) uint32 {
  29         minor := uint32((dev & 0x00000000000000ff) >> 0)
  30         minor |= uint32((dev & 0x00000ffffff00000) >> 12)
  31         return minor
  32 }
  33
  34 // Mkdev returns a Linux device number generated from the given major and minor
  35 // components.
  36 func Mkdev(major, minor uint32) uint64 {
  37         dev := (uint64(major) & 0x00000fff) << 8
  38         dev |= (uint64(major) & 0xfffff000) << 32
  39         dev |= (uint64(minor) & 0x000000ff) << 0
  40         dev |= (uint64(minor) & 0xffffff00) << 12
  41         return dev
  42 }