cubefs

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