// 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 }