title: Read/write from file descriptor at offset
body: <p>I've been using the <a href="http://linux.die.net/man/2/read" rel="noreferrer">read(2)</a> and <a href="http://linux.die.net/man/2/write" rel="noreferrer">write(2)</a> functions to read and write to a file given a file descriptor.</p>
  
  <p>Is there any function like this that allows you to put an offset into the file for read/write? </p>