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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"
"syscall"
)
const (
SEEK_DATA = 3
SEEK_HOLE = 4
SegmentHole = SegmentType(100)
SegmentData = SegmentType(101)
SegmentEOF = SegmentType(102)
)
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 _, s := range segments {
out += "\n" + s.String()
}
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)
if err == syscall.ENXIO {
segments = append(segments,
Segment{0, SegmentHole},
Segment{totalSize, SegmentEOF})
return segments, nil
}
if err != nil {
return nil, err
}
if off == cursor {
segments = append(segments, Segment{0, SegmentData})
} else {
segments = append(segments,
Segment{0, SegmentHole},
Segment{totalSize, SegmentData})
cursor = off
}
// now we are at the start of data.
// find next hole, then next data, then next hole, then next data...
for {
cursor, err = syscall.Seek(fd, cursor, SEEK_HOLE)
if err != nil {
return nil, err
}
if cursor == totalSize {
segments = append(segments, Segment{cursor, SegmentEOF})
break
}
segments = append(segments, Segment{cursor, SegmentHole})
cursor, err = syscall.Seek(fd, cursor, SEEK_DATA)
if err != nil {
return nil, err
}
if cursor == totalSize {
segments = append(segments, Segment{cursor, SegmentEOF})
break
}
segments = append(segments, Segment{cursor, SegmentData})
}
return segments, nil
}
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