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|
// Package holes finds and pretty-prints holes & data sections of a file.
// Used by TestFileHoleCopy in the gocryptfs test suite.
package holes
import (
"fmt"
"log"
"math/rand"
"os"
"syscall"
"time"
)
const (
SEEK_DATA = 3
SEEK_HOLE = 4
SegmentHole = SegmentType(100)
SegmentData = SegmentType(101)
SegmentEOF = SegmentType(102)
)
type Whence int
func (w Whence) String() string {
switch w {
case SEEK_DATA:
return "SEEK_DATA"
case SEEK_HOLE:
return "SEEK_HOLE"
default:
return "???"
}
}
type Segment struct {
Offset int64
Type SegmentType
}
func (s Segment) String() string {
return fmt.Sprintf("%10d %v", s.Offset, s.Type)
}
type SegmentType int
func (s SegmentType) String() string {
switch s {
case SegmentHole:
return "hole"
case SegmentData:
return "data"
case SegmentEOF:
return "eof"
default:
return "???"
}
}
// PrettyPrint pretty-prints the Segments.
func PrettyPrint(segments []Segment) (out string) {
for i, s := range segments {
out += s.String()
if i < len(segments)-1 {
out += "\n"
}
}
return out
}
// Find examines the file passed via file descriptor and returns the found holes
// and data sections.
func Find(fd int) (segments []Segment, err error) {
var st syscall.Stat_t
err = syscall.Fstat(fd, &st)
if err != nil {
return nil, err
}
totalSize := st.Size
var cursor int64
// find out if file starts with data or hole
off, err := syscall.Seek(fd, 0, SEEK_DATA)
// starts with hole and has no data
if err == syscall.ENXIO {
segments = append(segments,
Segment{0, SegmentHole},
Segment{totalSize, SegmentEOF})
return segments, nil
}
if err != nil {
return nil, err
}
// starts with data
if off == cursor {
segments = append(segments, Segment{0, SegmentData})
} else {
// starts with hole
segments = append(segments,
Segment{0, SegmentHole},
Segment{off, SegmentData})
cursor = off
}
// now we are at the start of data.
// find next hole, then next data, then next hole, then next data...
for {
oldCursor := cursor
// Next hole
off, err = syscall.Seek(fd, cursor, SEEK_HOLE)
if err != nil {
return nil, err
}
segments = append(segments, Segment{off, SegmentHole})
cursor = off
// Next data
off, err := syscall.Seek(fd, cursor, SEEK_DATA)
// No more data?
if err == syscall.ENXIO {
segments = append(segments,
Segment{totalSize, SegmentEOF})
break
}
if err != nil {
return nil, err
}
segments = append(segments, Segment{off, SegmentData})
cursor = off
if oldCursor == cursor {
return nil, fmt.Errorf("%s\nerror: seek loop!", PrettyPrint(segments))
}
}
return segments, nil
}
// Verify `segments` using a full bytewise file scan
func Verify(fd int, segments []Segment) (err error) {
last := segments[len(segments)-1]
if last.Type != SegmentEOF {
log.Panicf("BUG: last segment is not EOF. segments: %v", segments)
}
for i, s := range segments {
var whence int
switch s.Type {
case SegmentHole:
whence = SEEK_HOLE
case SegmentData:
whence = SEEK_DATA
case SegmentEOF:
continue
default:
log.Panicf("BUG: unknown segment type %d", s.Type)
}
for off := s.Offset; off < segments[i+1].Offset; off++ {
res, err := syscall.Seek(fd, off, whence)
if err != nil {
return fmt.Errorf("error: seek(%d, %s) returned error %v", off, Whence(whence).String(), err)
}
if res != off {
return fmt.Errorf("error: seek(%d, %s) returned new offset %d", off, Whence(whence).String(), res)
}
}
}
return err
}
// Create a test file at `path` with random holes
func Create(path string) {
f, err := os.OpenFile(path, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0600)
if err != nil {
panic(err)
}
defer f.Close()
rand.Seed(time.Now().UnixNano())
offsets := make([]int64, 10)
for i := range offsets {
offsets[i] = int64(rand.Int31n(60000))
}
buf := []byte("x")
for _, off := range offsets {
_, err = f.WriteAt(buf, off)
if err != nil {
panic(err)
}
}
// Expand the file to 50000 bytes so we sometimes have a hole on the end
if offsets[len(offsets)-1] < 50000 {
f.Truncate(50000)
}
f.Sync()
}
|
