text: // Copyright 2017 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  // Functions to access/create device major and minor numbers matching the
  // encoding used by the Linux kernel and glibc.
  //
  // The information below is extracted and adapted from bits/sysmacros.h in the
  // glibc sources:
  //
  // dev_t in glibc is 64-bit, with 32-bit major and minor numbers. glibc's
  // default encoding is MMMM Mmmm mmmM MMmm, where M is a hex digit of the major
  // number and m is a hex digit of the minor number. This is backward compatible
  // with legacy systems where dev_t is 16 bits wide, encoded as MMmm. It is also
  // backward compatible with the Linux kernel, which for some architectures uses
  // 32-bit dev_t, encoded as mmmM MMmm.
  
  package unix
  
  // Major returns the major component of a Linux device number.
  func Major(dev uint64) uint32 {
  	major := uint32((dev & 0x00000000000fff00) >> 8)
  	major |= uint32((dev & 0xfffff00000000000) >> 32)
  	return major
  }
  
  // Minor returns the minor component of a Linux device number.
  func Minor(dev uint64) uint32 {
  	minor := uint32((dev & 0x00000000000000ff) >> 0)
  	minor |= uint32((dev & 0x00000ffffff00000) >> 12)
  	return minor
  }
  
  // Mkdev returns a Linux device number generated from the given major and minor
  // components.
  func Mkdev(major, minor uint32) uint64 {
  	dev := (uint64(major) & 0x00000fff) << 8
  	dev |= (uint64(major) & 0xfffff000) << 32
  	dev |= (uint64(minor) & 0x000000ff) << 0
  	dev |= (uint64(minor) & 0xffffff00) << 12
  	return dev
  }
  