Function copy_file_range
fn copy_file_range<InFd: AsFd, OutFd: AsFd>(fd_in: InFd, off_in: Option<&mut u64>, fd_out: OutFd, off_out: Option<&mut u64>, len: usize) -> Result<usize>copy_file_range(fd_in, off_in, fd_out, off_out, len, 0)—Copies data
from one file to another.