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This is an automatically generated e-mail. To reply, visit:
<a href="https://reviewboard.asterisk.org/r/4528/">https://reviewboard.asterisk.org/r/4528/</a>
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<p style="margin-top: 0;">On March 31st, 2015, 10:28 a.m. CDT, <b>Mark Michelson</b> wrote:</p>
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<a href="https://reviewboard.asterisk.org/r/4528/diff/2/?file=72947#file72947line98" style="color: black; font-weight: bold; text-decoration: underline;">/trunk/main/dns_srv.c</a>
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(Diff revision 2)
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<td bgcolor="#c5ffc4" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "></pre></td>
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<td bgcolor="#c5ffc4" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "><span class="tb"> </span><span class="n">srv</span><span class="o">-></span><span class="n">priority</span> <span class="o">=</span> <span class="n">ntohs</span><span class="p">(</span><span class="n">srv_record</span><span class="o">-></span><span class="n">priority</span><span class="p">);</span></pre></td>
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<td bgcolor="#c5ffc4" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "><span class="tb"> </span><span class="n">srv</span><span class="o">-></span><span class="n">weight</span> <span class="o">=</span> <span class="n">ntohs</span><span class="p">(</span><span class="n">srv_record</span><span class="o">-></span><span class="n">weight</span><span class="p">);</span></pre></td>
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<td bgcolor="#c5ffc4" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "><span class="tb"> </span><span class="n">srv</span><span class="o">-></span><span class="n">port</span> <span class="o">=</span> <span class="n">ntohs</span><span class="p">(</span><span class="n">srv_record</span><span class="o">-></span><span class="n">port</span><span class="p">);</span></pre></td>
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<pre style="white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;">Let's talk alignment.
In DNS, there is no padding used for variable-length elements. There is no guarantee that RRs (or their RDATA) lie on word-boundaries. This means that the "data" pointer passed to ast_dns_srv_alloc() may be pointing to data that is not word-aligned (or not even on a half-word).
So in this case, you've overlaid a byte array on top of a struct that contains 16-bit unsigned integers. Typically, 16-bit values should be aligned on word or half-word boundaries, but because of the data layout of the DNS record, this cannot be guaranteed. This means you may be performing some unaligned reads here.
Now the question is, how bad is this? I'm pretty sure that on x86 architectures, an unaligned read isn't a big deal, performance-wise, but I can't make any claims for other architectures simply because I don't know. Can someone more familiar with these sorts of things chime in with some info?</pre>
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<pre style="margin-left: 1em; white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;">For x86 platforms, misaligned values are handled without a problem but with a performance penalty. On other processors such as the 68000 you get an alignment exception.</pre>
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<p>- rmudgett</p>
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<p>On March 26th, 2015, 1:50 p.m. CDT, Joshua Colp wrote:</p>
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<div>Review request for Asterisk Developers.</div>
<div>By Joshua Colp.</div>
<p style="color: grey;"><i>Updated March 26, 2015, 1:50 p.m.</i></p>
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<b style="color: #575012; font-size: 10pt;">Repository: </b>
Asterisk
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<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Description </h1>
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<pre style="margin: 0; padding: 0; white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;">This change adds the following:
1. As SRV records are added to a result the information is parsed and stored away in additional storage in the record. The SRV API can then be used to return this information.
2. Before invoking the DNS query callback the list of records on the result are sorted based on priority and weight.
3. Unit tests have been added which verify the record parsing, sorting, and weighting. There are also some off nominal which cover the cases when an invalid/corrupt record is received.
4. A unit test has also been added to res_resolver_unbound which adds an SRV record to a zone and confirms it is retrieved and parsed correctly.</pre>
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<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Testing </h1>
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<pre style="margin: 0; padding: 0; white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;">Executed unit tests and confirmed they pass.</pre>
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<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Diffs</b> </h1>
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<li>/trunk/tests/test_dns_srv.c <span style="color: grey">(PRE-CREATION)</span></li>
<li>/trunk/res/res_resolver_unbound.c <span style="color: grey">(433370)</span></li>
<li>/trunk/main/dns_srv.c <span style="color: grey">(433370)</span></li>
<li>/trunk/main/dns_core.c <span style="color: grey">(433370)</span></li>
<li>/trunk/include/asterisk/dns_internal.h <span style="color: grey">(433370)</span></li>
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<p><a href="https://reviewboard.asterisk.org/r/4528/diff/" style="margin-left: 3em;">View Diff</a></p>
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