title: how to extract file from a ext4 filesystem data?
body: <p>i have a XXX.img file.</p>
  
  <p>system.img: Linux rev 1.0 ext4 filesystem data, UUID=XXXX (extents) (large files)</p>
  
  <p>i want to extract some file from it, how?</p>
  
  <p>or XXX.subimg.tgz file</p>
  
  <p>first gunzip it, get subimg file, then as image file.</p>