1 package tar2ext4
2
3 import (
4 "bytes"
5 "crypto/rand"
6 "encoding/binary"
7 )
8
9
10 const (
11 cookieMagic = "conectix"
12 featureMask = 0x2
13 fileFormatVersionMagic = 0x00010000
14 fixedDataOffset = -1
15 creatorVersionMagic = 0x000a0000
16 diskTypeFixed = 2
17 )
18
19 type vhdFooter struct {
20 Cookie [8]byte
21 Features uint32
22 FileFormatVersion uint32
23 DataOffset int64
24 TimeStamp uint32
25 CreatorApplication [4]byte
26 CreatorVersion uint32
27 CreatorHostOS [4]byte
28 OriginalSize int64
29 CurrentSize int64
30 DiskGeometry uint32
31 DiskType uint32
32 Checksum uint32
33 UniqueID [16]uint8
34 SavedState uint8
35 Reserved [427]uint8
36 }
37
38 func makeFixedVHDFooter(size int64) *vhdFooter {
39 footer := &vhdFooter{
40 Features: featureMask,
41 FileFormatVersion: fileFormatVersionMagic,
42 DataOffset: fixedDataOffset,
43 CreatorVersion: creatorVersionMagic,
44 OriginalSize: size,
45 CurrentSize: size,
46 DiskType: diskTypeFixed,
47 UniqueID: generateUUID(),
48 }
49 copy(footer.Cookie[:], cookieMagic)
50 footer.Checksum = calculateCheckSum(footer)
51 return footer
52 }
53
54 func calculateCheckSum(footer *vhdFooter) uint32 {
55 oldchk := footer.Checksum
56 footer.Checksum = 0
57
58 buf := &bytes.Buffer{}
59 _ = binary.Write(buf, binary.BigEndian, footer)
60
61 var chk uint32
62 bufBytes := buf.Bytes()
63 for i := 0; i < len(bufBytes); i++ {
64 chk += uint32(bufBytes[i])
65 }
66 footer.Checksum = oldchk
67 return uint32(^chk)
68 }
69
70 func generateUUID() [16]byte {
71 res := [16]byte{}
72 if _, err := rand.Read(res[:]); err != nil {
73 panic(err)
74 }
75 return res
76 }
77
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