<p>This analysis verifies by reproducible analysis a set of specific contributions that are clearly made by Christoph Hellwig to Linux, and shows how those contributions appear in the VMware ESXi 5.5 product.</p>

<p>This analysis was prepared and written by <a href="https://sfconservancy.org/about/staff/#bkuhn">Bradley M. Kuhn</a>.</p>

<h1 id="understanding-code-similarity-and-cloning">Understanding Code Similarity and &quot;Cloning&quot;</h1>

<p>Software is often modified in various ways; indeed, Linux developers form a community that encourages and enables modification by many parties. Given this development model, communities often find it valuable to determine when software source code moves from one place to another with only minor modifications. Various scientifically-vetted techniques can be used to identify &quot;clones&quot; -- a portion of code that is substantially similar to pre-existing source code. The specific area of academic research is called &quot;code cloning detection&quot; or &quot;code duplication detection&quot;. The area has been under active research since the mid-1990s <a href="#fn1" class="footnoteRef" id="fnref1"><sup>1</sup></a>. In 2002, Japanese researchers published a tool called CCFinder <a href="#fn2" class="footnoteRef" id="fnref2"><sup>2</sup></a>, which, in its updated incarnation (called CCFinderX), is widely used and referenced by academic researchers in the field <a href="#fn3" class="footnoteRef" id="fnref3"><sup>3</sup></a> and has specifically been used to explore reuses of code in GPL'd software such as Linux <a href="#fn4" class="footnoteRef" id="fnref4"><sup>4</sup></a>.</p>

<p>CCFinderX uses a token-based clone detection method and a suffix-tree matching algorithm; both techniques have been highly vetted and considered in the academic literature. The techniques are considered viable and useful in detecting clones. Many academic papers on the subject have been peer-reviewed and published, and nearly every newly published paper compares its new techniques of clone detection to the seminal results found by CCFinderX. For purposes of our analysis, we have therefore chosen to use CCFinderX. These results can be easily reproduced since CCFinderX is, itself, also Open Source software.</p>

<h1 id="establishing-a-baseline-of-the-ccfinderx-tool">Establishing A Baseline of the CCFinderX Tool</h1>

<p>The experiment confirmed the hypothesis. We found that a 3.68% &quot;ratio of similarity&quot; when comparing code from Linux to the FreeBSD kernel.</p>

<p>Next, we compared the source code of the Linux Kernel 4.5.2 to the LLVM+Clang system, version 3.8.0. These two projects are each a large program written in the C programming language, but they are not known to actively share code. We would expect some very minimal similarity simply due to chance, but something much lower than the 3.68% found between Linux and FreeBSD's kernel.</p>

<p>Indeed, when the same test is run to compare Linux to the LLVM+Clang system, the &quot;ratio of similarity&quot; was 0.075%.</p>

<h1 id="general-comparison-of-linux-kernel-to-vmware-sources">General Comparison of Linux Kernel to VMware sources</h1>

<p>With the baseline established, we now begin relevant comparisons. First, we compare the Linux kernel version 2.6.34 to the sources <a href="http://k.sfconservancy.org/vmkdrivers">released by VMware in their (partial) source release</a>. The &quot;ratio of similarity&quot; between Linux 2.6.34 and VMware's partial source release is 20.72%. There is little question that much of VMware's kernel has come from Linux.</p>

<h1 id="methodology-of-showing-hellwigs-contributions-in-vmware-esxi-5.5-sources">Methodology Of Showing Hellwig's Contributions in VMware ESXi 5.5 Sources</h1>