<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 released by VMware in their (partial) source release. 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>

<p>The following describes a methodology to show Hellwig's contributions to Linux, and how they compare to code found in VMware ESXi 5.5.</p>

<h2 id="extracting-hellwigs-contributions-from-linux-historical-repository">Extracting Hellwig's Contributions From Linux Historical Repository</h2>

<p>Excellent records exist of contributions made to Linux from 2002-02-04 through present date. From 2002-02-04 through 2005-04-03, Bitkeeper was used to store revision control history of Linux. Each improvement contributed to Linux has information regarding who placed the contribution in Linux, and a comment field in which the contributor can credit others, such as by noting that the contribution actually came from someone else.</p>

<p>I extracted from the historical Linux tree the identifying number of all commits that are either made with Hellwig in the official Author field, or where the person in the Author field left notes clearly indicating that the contribution was done by Hellwig. For the latter, the following regular expression search against the log file was used:</p>

<pre><code>(Submitted\s+by|original\s+patch|patch\s+(from|by)|originally\s+(from|by)).*Hellwig</code></pre>

<p>Specifically, I used <a href="https://github.com/conservancy/gpl-compliance-tools/blob/master/commit-id-list-matching-regex.plx">a script</a> to extract a list of commit ids from the <a href="git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git">historical Linux repository</a>. This method found 1,012 separate occasions of contribution by Hellwig from 2002-02-04 through 2005-04-03.</p>

<p>After finding these separate occasions of contribution, I then extracted the source code lines that Hellwig added or changed in each contribution in this repository. I did so by carefully cross-referencing the commits that Hellwig performed with the output of <code>git blame</code>. I specifically <a href="https://github.com/conservancy/gpl-compliance-tools/blob/master/extract-code-added-in-commits.plx">wrote a script</a> to carefully extracted only lines that Hellwig changed or added in that repository, and placed only those contributions identifiable as Hellwig's into new files whose named matched the original filenames. This created a corpus of code that can be verifiable as added or changed by Hellwig and no one else.</p>

<p>Note: e40152ee1e1c7a63f4777791863215e3faa37a86 is the 2.6.34 version created by Linus Torvalds <script type="text/javascript">

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<h2 id="comparing-hellwigs-contributions-from-linux-historical-repository-to-vmware-sources">Comparing Hellwig's Contributions From Linux Historical Repository to VMware Sources</h2>

<p>I then used this corpus as input to CCFinderX (similar to the other CCFinderX comparisons explained earlier). Specifically, this CCFinderX comparison compared all known Hellwig-contributed material from the historical Linux repository to the partial VMware source release. CCFinderX found a ratio of similarity of 0.0900% between Hellwig's code and the source code in VMware's (partial) source release. CCFinderX specifically identified 12 distinct locations where substantial sections of code contributed by Hellwig appeared in VMware's code.</p>

<p>Most notably, substantial portions of the the following core SCSI functions were found by this search technique: <code>__scsi_device_lookup</code> and <code>__scsi_get_command</code>, <code>mpt_get_product_name</code>, <code>scsi_proc_host_rm</code>, <code>mega_enum_raid_scsi</code>, <code>mega_m_to_n</code>, <code>mega_prepare_passthru</code>, <code>proc_scsi_show</code>, and <code>__down_read_trylock</code>.</p>

<h2 id="extracting-hellwigs-contributions-from-modern-linux-repository">Extracting Hellwig's Contributions From Modern Linux Repository</h2>

<p>Beginning on 2005-04-16, Linux began using the new Git system to store revision history. This history can be analyzed in a similar fashion as was done for the historical repository.</p>

<p>In this case, I picked a specific revision to center the analysis, the Linux 2.6.34 release from 2010-05-16. For the period from 2005-04-16 through 2010-05-16, I extracted from the modern Linux tree the identifying number of all commits that are either made with Hellwig in the official Author field, or where the person in the Author field left notes clearly indicating that the contribution was done by Hellwig. For the latter, the following regular expression search against the log file was used (as before):</p>