dev_linux.go raw

   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  }
  43