func coalesce(parentFile *os.File, childFile *os.File) error {
blockSize, err := getFileSystemBlockSize(childFile)
if err != nil {
panic("can't get FS block size, error: " + err.Error())
}
var data, hole int64
for {
data, err = syscall.Seek(int(childFile.Fd()), hole, seekData)
if err != nil {
// reaches EOF
errno := err.(syscall.Errno)
if errno == syscall.ENXIO {
break
} else {
// unexpected errors
log.Fatal("Failed to syscall.Seek SEEK_DATA")
return err
}
}
hole, err = syscall.Seek(int(childFile.Fd()), data, seekHole)
if err != nil {
log.Fatal("Failed to syscall.Seek SEEK_HOLE")
return err
}
// now we have a data start offset and length(hole - data)
// let's read from child and write to parent file block by block
_, err = parentFile.Seek(data, os.SEEK_SET)
if err != nil {
log.Fatal("Failed to os.Seek os.SEEK_SET")
return err
}
offset := data
buffer := fio.AllocateAligned(blockSize)
for offset != hole {
// read a block from child, maybe use bufio or Reader stream
n, err := fio.ReadAt(childFile, buffer, offset)
if n != len(buffer) || err != nil {
log.Fatal("Failed to read from childFile")
return err
}
// write a block to parent
n, err = fio.WriteAt(parentFile, buffer, offset)
if n != len(buffer) || err != nil {
log.Fatal("Failed to write to parentFile")
return err
}
offset += int64(n)
}
}
return nil
}
func (d *directFile) WriteAt(buf []byte, offset int64) (int, error) {
return directfio.WriteAt(d.File, buf, offset)
}