title: Is there a minimal set of files to keep from a Linux kernel compile for compiling kernel modules later, as needed?
body: <p>After I compile a linux kernel, I need to keep the huge souce directory in my disk for the further external module's compiling.</p>
  
  <p>I can not simply run <strong>make clean</strong>,  because this fails me when I compile some modules in this way: </p>
  
  <pre><code>$ make -C /lib/modules/`uname -r`/build
  </code></pre>
  
  <p>I roughly read the Makefile of kernel source, but there seems not a target to do this work.</p>
  
  <p>Question:</p>
  
  <p><strong>What files are valuable that I should copy from the working linux source directory for the further use of compiling external module?</strong></p>