Copying data from disk to disk using direct io

direct_copy.py

import mmap
import io

from contextlib import closing

BUF_SIZE = 8 * 1024**2

buf = mmap.mmap(-1, BUF_SIZE)
with closing(buf), io.FileIO(src_path, "r") as src, io.FileIO(dst_path, "r+") as dst:
  while True:
    read = src.readinto(buf)
    if read == 0:
      break  # done
    written = 0
    while written < read:
      wbuf = buffer(buf, written, read - written)
      written += dst.write(wbuf)