findholes: add --create, --verify
Also, change the logic for the segment walk to not rely on the total size. cp does not use the total size either, and we miss bugs by cheating!
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07164cbb3a
commit
c1d7e38761
@ -4,7 +4,11 @@ package holes
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import (
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"fmt"
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"log"
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"math/rand"
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"os"
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"syscall"
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"time"
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)
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const (
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@ -16,6 +20,19 @@ const (
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SegmentEOF = SegmentType(102)
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)
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type Whence int
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func (w Whence) String() string {
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switch w {
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case SEEK_DATA:
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return "SEEK_DATA"
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case SEEK_HOLE:
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return "SEEK_HOLE"
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default:
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return "???"
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}
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}
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type Segment struct {
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Offset int64
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Type SegmentType
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@ -42,8 +59,11 @@ func (s SegmentType) String() string {
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// PrettyPrint pretty-prints the Segments.
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func PrettyPrint(segments []Segment) (out string) {
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for _, s := range segments {
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out += "\n" + s.String()
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for i, s := range segments {
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out += s.String()
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if i < len(segments)-1 {
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out += "\n"
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}
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}
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return out
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}
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@ -62,6 +82,7 @@ func Find(fd int) (segments []Segment, err error) {
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// find out if file starts with data or hole
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off, err := syscall.Seek(fd, 0, SEEK_DATA)
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// starts with hole and has no data
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if err == syscall.ENXIO {
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segments = append(segments,
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Segment{0, SegmentHole},
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@ -71,36 +92,108 @@ func Find(fd int) (segments []Segment, err error) {
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if err != nil {
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return nil, err
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}
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// starts with data
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if off == cursor {
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segments = append(segments, Segment{0, SegmentData})
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} else {
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// starts with hole
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segments = append(segments,
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Segment{0, SegmentHole},
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Segment{totalSize, SegmentData})
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Segment{off, SegmentData})
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cursor = off
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}
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// now we are at the start of data.
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// find next hole, then next data, then next hole, then next data...
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for {
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cursor, err = syscall.Seek(fd, cursor, SEEK_HOLE)
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oldCursor := cursor
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// Next hole
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off, err = syscall.Seek(fd, cursor, SEEK_HOLE)
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if err != nil {
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return nil, err
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}
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if cursor == totalSize {
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segments = append(segments, Segment{cursor, SegmentEOF})
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break
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segments = append(segments, Segment{off, SegmentHole})
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cursor = off
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// Next data
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off, err := syscall.Seek(fd, cursor, SEEK_DATA)
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// No more data?
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if err == syscall.ENXIO {
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segments = append(segments,
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Segment{totalSize, SegmentEOF})
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return segments, nil
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}
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segments = append(segments, Segment{cursor, SegmentHole})
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cursor, err = syscall.Seek(fd, cursor, SEEK_DATA)
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if err != nil {
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return nil, err
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}
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if cursor == totalSize {
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segments = append(segments, Segment{cursor, SegmentEOF})
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break
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segments = append(segments, Segment{off, SegmentData})
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cursor = off
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if oldCursor == cursor {
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return nil, fmt.Errorf("%s\nerror: seek loop!", PrettyPrint(segments))
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}
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segments = append(segments, Segment{cursor, SegmentData})
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}
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return segments, nil
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}
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// Verify the gives `segments` using a full bytewise file scan
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func Verify(fd int, segments []Segment) (err error) {
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last := segments[len(segments)-1]
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if last.Type != SegmentEOF {
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log.Panicf("BUG: last segment is not EOF. segments: %v", segments)
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}
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for i, s := range segments {
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var whence int
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switch s.Type {
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case SegmentHole:
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whence = SEEK_HOLE
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case SegmentData:
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whence = SEEK_DATA
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case SegmentEOF:
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continue
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default:
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log.Panicf("BUG: unkown segment type %d", s.Type)
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}
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for off := s.Offset; off < segments[i+1].Offset; off++ {
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res, err := syscall.Seek(fd, off, whence)
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if err != nil {
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return fmt.Errorf("error: seek(%d, %s) returned error %v", off, Whence(whence).String(), err)
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}
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if res != off {
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return fmt.Errorf("error: seek(%d, %s) returned new offset %d", off, Whence(whence).String(), res)
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}
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}
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}
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return err
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}
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// Create a test file at `path` with random holes
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func Create(path string) {
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f, err := os.OpenFile(path, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0600)
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if err != nil {
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panic(err)
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}
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defer f.Close()
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rand.Seed(time.Now().UnixNano())
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offsets := make([]int64, 10)
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for i := range offsets {
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offsets[i] = int64(rand.Int31n(60000))
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}
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buf := []byte("x")
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for _, off := range offsets {
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_, err = f.WriteAt(buf, off)
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if err != nil {
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panic(err)
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}
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}
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// Expand the file to 50000 bytes so we sometimes have a hole on the end
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if offsets[len(offsets)-1] < 50000 {
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f.Truncate(50000)
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}
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f.Sync()
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}
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@ -10,13 +10,25 @@ import (
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)
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func main() {
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flags := struct {
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verify *bool
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create *bool
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}{}
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flags.verify = flag.Bool("verify", false, "Verify results using full file scan")
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flags.create = flag.Bool("create", false, "Create test file with random holes")
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flag.Parse()
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if flag.NArg() != 1 {
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fmt.Printf("Usage: findholes FILE\n")
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os.Exit(1)
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}
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f, err := os.Open(flag.Arg(0))
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path := flag.Arg(0)
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if *flags.create {
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holes.Create(path)
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}
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f, err := os.Open(path)
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if err != nil {
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// os.Open() gives nicer error messages than syscall.Open()
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fmt.Println(err)
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@ -31,4 +43,15 @@ func main() {
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}
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fmt.Println(holes.PrettyPrint(segments))
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if *flags.verify {
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err = holes.Verify(int(f.Fd()), segments)
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if err != nil {
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fmt.Println(err)
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os.Exit(1)
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} else {
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fmt.Println("verify ok")
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}
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}
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}
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