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//go:build linux
package guestdisk
import (
"errors"
"io"
"os"
"golang.org/x/sys/unix"
)
const copyChunk = 1 << 20
func cloneInto(out, in *os.File) error {
if err := unix.IoctlFileClone(int(out.Fd()), int(in.Fd())); err == nil {
return nil
}
info, err := in.Stat()
if err != nil {
return err
}
size := info.Size()
for offset := int64(0); offset < size; {
data, err := unix.Seek(int(in.Fd()), offset, unix.SEEK_DATA)
if errors.Is(err, unix.ENXIO) {
break
}
if err != nil {
if _, err := in.Seek(0, io.SeekStart); err != nil {
return err
}
if _, err := io.Copy(out, in); err != nil {
return err
}
return out.Truncate(size)
}
hole, err := unix.Seek(int(in.Fd()), data, unix.SEEK_HOLE)
if err != nil {
hole = size
}
if err := copyExtent(out, in, data, hole-data); err != nil {
return err
}
offset = hole
}
return out.Truncate(size)
}
func copyExtent(out, in *os.File, offset, length int64) error {
buf := make([]byte, copyChunk)
for done := int64(0); done < length; {
want := min(length-done, copyChunk)
n, err := in.ReadAt(buf[:want], offset+done)
if n > 0 {
if _, writeErr := out.WriteAt(buf[:n], offset+done); writeErr != nil {
return writeErr
}
done += int64(n)
}
if err != nil {
if errors.Is(err, io.EOF) {
return nil
}
return err
}
}
return nil
}
