title: What's #define LINUX for?
body: <p>I'm writing a char device driver for Linux, and I saw in some example the following lines  </p>
  
  <pre><code>    #define __KERNEL__             
      #define MODULE                             
      #define LINUX
  </code></pre>
  
  <p>I found in the internet that <code>#define __KERNEL__</code> means that the code is part of the kernel, and that <code>#define MODULE</code> means that it's not a permanent part, but for some reason I can't find what <code>#define LINUX</code> is for?<br>
  In some examples I saw only the first two defines, and in other all the three defines.</p>
  
  <p>So my question is: what is  <code>#define LINUX</code> for?</p>