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feat: Use tar i compatible archive format

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This commit is contained in:
Felicitas Pojtinger
2021-11-16 11:21:36 +01:00
parent e272a464b8
commit 8e9b874304
3 changed files with 142 additions and 50 deletions
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122
cmd/stfs-tvf-simple-tape/main.go Normal file
View File

@@ -0,0 +1,122 @@
package main
import (
"archive/tar"
"bufio"
"flag"
"io"
"log"
"os"
"syscall"
"unsafe"
)
// See https://github.com/benmcclelland/mtio
const (
MTIOCPOS = 0x80086d03 // Get tape position
blockSize = 512
)
// Position is struct for MTIOCPOS
type Position struct {
BlkNo int64 // Current block number
}
func main() {
file := flag.String("file", "/dev/nst0", "File (tape drive or tar file) to open")
recordSize := flag.Int("recordSize", 20, "Amount of 512-bit blocks per record")
flag.Parse()
fileDescription, err := os.Stat(*file)
if err != nil {
panic(err)
}
var f *os.File
if fileDescription.Mode().IsRegular() {
f, err = os.Open(*file)
if err != nil {
panic(err)
}
} else {
f, err = os.OpenFile(*file, os.O_RDONLY, os.ModeCharDevice)
if err != nil {
panic(err)
}
}
defer f.Close()
br := bufio.NewReaderSize(f, blockSize**recordSize)
tr := tar.NewReader(br)
record := int64(0)
block := int64(0)
for {
hdr, err := tr.Next()
if err != nil {
if err == io.EOF {
break
}
// Seek one block backwards (half into the trailer) into trailer
if fileDescription.Mode().IsRegular() {
if _, err := f.Seek((int64(*recordSize)*blockSize*record)+block*blockSize, io.SeekStart); err == nil {
tr = tar.NewReader(br)
hdr, err = tr.Next()
if err != nil {
panic(err)
}
} else {
panic(err)
}
} else {
panic(err)
}
}
curr := int64(0)
if fileDescription.Mode().IsRegular() {
curr, err = f.Seek(0, io.SeekCurrent)
if err != nil {
panic(err)
}
} else {
pos := &Position{}
syscall.Syscall(
syscall.SYS_IOCTL,
f.Fd(),
MTIOCPOS,
uintptr(unsafe.Pointer(pos)),
)
// TODO: Ensure that this is in fact the block, not just the record
curr = pos.BlkNo * blockSize
}
if record == 0 && block == 0 {
log.Println("Record:", 0, "Block:", 0, "Header:", hdr)
} else {
log.Println("Record:", record, "Block:", block, "Header:", hdr)
}
nextTotalBlocks := (curr + hdr.Size) / blockSize
if record == 0 && block == 0 {
record = nextTotalBlocks / int64(*recordSize)
block = nextTotalBlocks - (record * int64(*recordSize)) // For the first record, the offset of one is not needed
} else {
record = nextTotalBlocks / int64(*recordSize)
block = nextTotalBlocks - (record * int64(*recordSize)) + 1 // +1 because we need to start reading right after the last block
}
if block > int64(*recordSize) {
record++
block = 0
}
}
}

29
cmd/stfs-tvf-simple/main.go
View File

@@ -41,22 +41,31 @@ func main() {
record := int64(0)
block := int64(0)
firstRecordOfArchive := int64(0)
for {
hdr, err := tr.Next()
if err != nil {
if err == io.EOF {
break
}
// Seek one block backwards (half into the trailer) into trailer
if _, err := f.Seek((int64(*recordSize)*blockSize*record)+block*blockSize, io.SeekStart); err == nil {
// Seek right after the next two blocks to skip the trailer
if _, err := f.Seek((int64(*recordSize)*blockSize*record)+(block+1)*blockSize, io.SeekStart); err == nil {
tr = tar.NewReader(f)
hdr, err = tr.Next()
if err != nil {
if err == io.EOF {
break
}
panic(err)
}
block++
if block > int64(*recordSize) {
record++
block = 0
}
firstRecordOfArchive = record
} else {
panic(err)
}
@@ -77,13 +86,11 @@ func main() {
}
nextTotalBlocks := (curr + hdr.Size) / blockSize
record = nextTotalBlocks / int64(*recordSize)
// TODO: This currently returns one block to little on appended tar archives
if record == 0 && block == 0 {
record = nextTotalBlocks / int64(*recordSize)
block = nextTotalBlocks - (record * int64(*recordSize)) // For the first record, the offset of one is not needed
if record == 0 && block == 0 || record == firstRecordOfArchive {
block = nextTotalBlocks - (record * int64(*recordSize)) // For the first record of the file or archive, the offset of one is not needed
} else {
record = nextTotalBlocks / int64(*recordSize)
block = nextTotalBlocks - (record * int64(*recordSize)) + 1 // +1 because we need to start reading right after the last block
}

41
cmd/stfs-uvf-with-header/main.go
View File

@@ -39,17 +39,12 @@ type Operation struct {
Count int32 // Operation count
}
const (
blockSize = 512
)
func main() {
file := flag.String("file", "/dev/nst0", "File (tape drive or tar file) to open")
dir := flag.String("dir", ".", "Directory to add to the file")
flag.Parse()
seekBackwards := int64(-blockSize) // Seek back one block (half a trailer) so we can detect the invalid trailer in `tvf` and seek accordingly
isRegular := true
stat, err := os.Stat(*file)
if err == nil {
@@ -57,20 +52,6 @@ func main() {
} else {
if os.IsNotExist(err) {
isRegular = true
// Create the file
f, err := os.OpenFile(*file, os.O_APPEND|os.O_WRONLY|os.O_CREATE, 0600)
if err != nil {
panic(err)
}
// Create an empty tar archive with a trailer so that we may seek back
tw := tar.NewWriter(f)
if err := tw.Close(); err != nil {
panic(err)
}
seekBackwards = -(blockSize * 2) // Overwrite the file completely the first time
} else {
panic(err)
}
@@ -78,15 +59,12 @@ func main() {
var f *os.File
if isRegular {
f, err = os.OpenFile(*file, os.O_RDWR, 0600)
f, err = os.OpenFile(*file, os.O_APPEND|os.O_WRONLY|os.O_CREATE, 0600)
if err != nil {
panic(err)
}
// Seek backwards into header
if _, err := f.Seek(seekBackwards, io.SeekEnd); err != nil {
panic(err)
}
// No need to go to end manually due to `os.O_APPEND`
} else {
// Go to end of file
syscall.Syscall(
@@ -104,21 +82,6 @@ func main() {
if err != nil {
panic(err)
}
// Seek backwards into header
// TODO: Validate that this iterates by block, not by record
// TODO: Only run this if output of tell syscall != 0
syscall.Syscall(
syscall.SYS_IOCTL,
f.Fd(),
MTIOCTOP,
uintptr(unsafe.Pointer(
&Operation{
Op: MTBSR,
Count: 1,
},
)),
)
}
defer f.Close()