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
