title: Please explain what this piece of C code does
body: <p>Can someone explain what is this piece of code do?</p>
  
  <pre><code>pa_offset = offset &amp; ~(sysconf(_SC_PAGE_SIZE) - 1);
  
  /* offset for mmap() must be page aligned */
  </code></pre>
  
  <p>I understand that here <code>sysconf</code> returns the page size, which lets assume that it is 4096, but after that I am not able to understand the logic. Thanks in advance.</p>