| Don Newton | 98fd881 | 2019-09-23 15:15:02 -0400 | [diff] [blame^] | 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 | } |