mirror of
https://gitlab.com/libvirt/libvirt.git
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78b139b0bd
Enforce and document the style set up by the previous patches. * build-aux/bracket-spacing.pl: Add comma checks. * docs/hacking.html.in: Document the rules. * HACKING: Regenerate. Signed-off-by: Eric Blake <eblake@redhat.com>
1191 lines
40 KiB
XML
1191 lines
40 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<body>
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<h1>Contributor guidelines</h1>
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<ul id="toc"></ul>
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<h2><a name="patches">General tips for contributing patches</a></h2>
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<ol>
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<li>Discuss any large changes on the mailing list first. Post patches
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early and listen to feedback.</li>
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<li><p>Post patches in unified diff format, with git rename
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detection enabled. You need a one-time setup of:</p>
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<pre>
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git config diff.renames true
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</pre>
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<p>After that, a command similar to this should work:</p>
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<pre>
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diff -urp libvirt.orig/ libvirt.modified/ > libvirt-myfeature.patch
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</pre>
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<p>
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or:
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</p>
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<pre>
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git diff > libvirt-myfeature.patch
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</pre>
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<p>Also, for code motion patches, you may find that <code>git
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diff --patience</code> provides an easier-to-read patch.
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However, the usual workflow of libvirt developer is:</p>
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<pre>
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git checkout master
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git pull
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git checkout -t origin -b workbranch
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Hack, committing any changes along the way
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</pre>
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<p>More hints on compiling can be
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found <a href="compiling.html">here</a>. When you want to
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post your patches:</p>
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<pre>
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git pull --rebase
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(fix any conflicts)
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git send-email --cover-letter --no-chain-reply-to --annotate \
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--to=libvir-list@redhat.com master
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</pre>
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<p>(Note that the "git send-email" subcommand may not be in
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the main git package and using it may require installation of a
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separate package, for example the "git-email" package in
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Fedora.) For a single patch you can omit
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<code>--cover-letter</code>, but a series of two or more
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patches needs a cover letter. If you get tired of typing
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<code>--to=libvir-list@redhat.com</code> designation you can
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set it in git config:</p>
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<pre>
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git config sendemail.to libvir-list@redhat.com
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</pre>
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<p>Please follow this as close as you can, especially the rebase and
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git send-email part, as it makes life easier for other developers to
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review your patch set. One should avoid sending patches as attachments,
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but rather send them in email body along with commit message. If a
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developer is sending another version of the patch (e.g. to address
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review comments), he is advised to note differences to previous
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versions after the <code>---</code> line in the patch so that it helps
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reviewers but doesn't become part of git history. Moreover, such patch
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needs to be prefixed correctly with
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<code>--subject-prefix=PATCHv2</code> appended to <code>git
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send-email</code> (substitute <code>v2</code> with the correct
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version if needed though).</p>
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</li>
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<li><p>In your commit message, make the summary line reasonably
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short (60 characters is typical), followed by a blank line,
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followed by any longer description of why your patch makes
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sense. If the patch fixes a regression, and you know what
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commit introduced the problem, mentioning that is useful.
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If the patch resolves a bugzilla report, mentioning the URL
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of the bug number is useful; but also summarize the issue
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rather than making all readers follow the link. You can use
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'git shortlog -30' to get an idea of typical summary lines.
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Libvirt does not currently attach any meaning to
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Signed-off-by: lines, so it is up to you if you want to
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include or omit them in the commit message.
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</p>
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</li>
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<li><p>Split large changes into a series of smaller patches,
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self-contained if possible, with an explanation of each patch
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and an explanation of how the sequence of patches fits
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together. Moreover, please keep in mind that it's required to
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be able to compile cleanly (<b>including</b> <code>make
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check</code> and <code>make syntax-check</code>) after each
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patch. A feature does not have to work until the end of a
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series, but intermediate patches must compile and not cause
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test-suite failures (this is to preserve the usefulness
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of <code>git bisect</code>, among other things).</p>
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</li>
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<li>Make sure your patches apply against libvirt GIT. Developers
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only follow GIT and don't care much about released versions.</li>
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<li><p>Run the automated tests on your code before submitting any changes.
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In particular, configure with compile warnings set to
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-Werror. This is done automatically for a git checkout; from a
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tarball, use:</p>
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<pre>
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./configure --enable-werror
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</pre>
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<p>
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and run the tests:
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</p>
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<pre>
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make check
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make syntax-check
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make -C tests valgrind
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</pre>
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<p><a href="http://valgrind.org/">Valgrind</a> is a test that checks
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for memory management issues, such as leaks or use of uninitialized
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variables.
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</p>
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<p>
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Some tests are skipped by default in a development environment,
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based on the time they take in comparison to the likelihood
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that those tests will turn up problems during incremental builds.
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These tests default to being run when when building from a
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tarball or with the configure option --enable-expensive-tests;
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you can also force a one-time toggle of these tests by
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setting VIR_TEST_EXPENSIVE to 0 or 1 at make time, as in:
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</p>
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<pre>
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make check VIR_TEST_EXPENSIVE=1
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</pre>
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<p>
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If you encounter any failing tests, the VIR_TEST_DEBUG
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environment variable may provide extra information to debug
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the failures. Larger values of VIR_TEST_DEBUG may provide
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larger amounts of information:
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</p>
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<pre>
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VIR_TEST_DEBUG=1 make check (or)
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VIR_TEST_DEBUG=2 make check
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</pre>
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<p>
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When debugging failures during development, it is possible
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to focus in on just the failing subtests by using TESTS and
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VIR_TEST_RANGE:
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</p>
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<pre>
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make check VIR_TEST_DEBUG=1 VIR_TEST_RANGE=3-5 TESTS=qemuxml2argvtest
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</pre>
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<p>
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Also, individual tests can be run from inside the <code>tests/</code>
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directory, like:
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</p>
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<pre>
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./qemuxml2xmltest
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</pre>
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<p>There is also a <code>./run</code> script at the top level,
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to make it easier to run programs that have not yet been
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installed, as well as to wrap invocations of various tests
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under gdb or Valgrind.
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</p>
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</li>
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<li><p>The Valgrind test should produce similar output to
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<code>make check</code>. If the output has traces within libvirt
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API's, then investigation is required in order to determine the
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cause of the issue. Output such as the following indicates some
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sort of leak:
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</p>
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<pre>
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==5414== 4 bytes in 1 blocks are definitely lost in loss record 3 of 89
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==5414== at 0x4A0881C: malloc (vg_replace_malloc.c:270)
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==5414== by 0x34DE0AAB85: xmlStrndup (in /usr/lib64/libxml2.so.2.7.8)
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==5414== by 0x4CC97A6: virDomainVideoDefParseXML (domain_conf.c:7410)
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==5414== by 0x4CD581D: virDomainDefParseXML (domain_conf.c:10188)
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==5414== by 0x4CD8C73: virDomainDefParseNode (domain_conf.c:10640)
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==5414== by 0x4CD8DDB: virDomainDefParse (domain_conf.c:10590)
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==5414== by 0x41CB1D: testCompareXMLToArgvHelper (qemuxml2argvtest.c:100)
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==5414== by 0x41E20F: virtTestRun (testutils.c:161)
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==5414== by 0x41C7CB: mymain (qemuxml2argvtest.c:866)
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==5414== by 0x41E84A: virtTestMain (testutils.c:723)
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==5414== by 0x34D9021734: (below main) (in /usr/lib64/libc-2.15.so)
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</pre>
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<p>In this example, the <code>virDomainDefParseXML()</code> had
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an error path where the <code>virDomainVideoDefPtr video</code>
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pointer was not properly disposed. By simply adding a
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<code>virDomainVideoDefFree(video);</code> in the error path,
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the issue was resolved.
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</p>
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<p>Another common mistake is calling a printing function, such as
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<code>VIR_DEBUG()</code> without initializing a variable to be
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printed. The following example involved a call which could return
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an error, but not set variables passed by reference to the call.
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The solution was to initialize the variables prior to the call.
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</p>
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<pre>
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==4749== Use of uninitialised value of size 8
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==4749== at 0x34D904650B: _itoa_word (in /usr/lib64/libc-2.15.so)
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==4749== by 0x34D9049118: vfprintf (in /usr/lib64/libc-2.15.so)
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==4749== by 0x34D9108F60: __vasprintf_chk (in /usr/lib64/libc-2.15.so)
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==4749== by 0x4CAEEF7: virVasprintf (stdio2.h:199)
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==4749== by 0x4C8A55E: virLogVMessage (virlog.c:814)
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==4749== by 0x4C8AA96: virLogMessage (virlog.c:751)
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==4749== by 0x4DA0056: virNetTLSContextCheckCertKeyUsage (virnettlscontext.c:225)
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==4749== by 0x4DA06DB: virNetTLSContextCheckCert (virnettlscontext.c:439)
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==4749== by 0x4DA1620: virNetTLSContextNew (virnettlscontext.c:562)
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==4749== by 0x4DA26FC: virNetTLSContextNewServer (virnettlscontext.c:927)
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==4749== by 0x409C39: testTLSContextInit (virnettlscontexttest.c:467)
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==4749== by 0x40AB8F: virtTestRun (testutils.c:161)
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</pre>
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<p>Valgrind will also find some false positives or code paths
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which cannot be resolved by making changes to the libvirt code.
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For these paths, it is possible to add a filter to avoid the
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errors. For example:
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</p>
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<pre>
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==4643== 7 bytes in 1 blocks are possibly lost in loss record 4 of 20
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==4643== at 0x4A0881C: malloc (vg_replace_malloc.c:270)
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==4643== by 0x34D90853F1: strdup (in /usr/lib64/libc-2.15.so)
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==4643== by 0x34EEC2C08A: ??? (in /usr/lib64/libnl.so.1.1)
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==4643== by 0x34EEC15B81: ??? (in /usr/lib64/libnl.so.1.1)
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==4643== by 0x34D8C0EE15: call_init.part.0 (in /usr/lib64/ld-2.15.so)
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==4643== by 0x34D8C0EECF: _dl_init (in /usr/lib64/ld-2.15.so)
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==4643== by 0x34D8C01569: ??? (in /usr/lib64/ld-2.15.so)
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</pre>
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<p>In this instance, it is acceptable to modify the
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<code>tests/.valgrind.supp</code> file in order to add a
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suppression filter. The filter should be unique enough to
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not suppress real leaks, but it should be generic enough to
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cover multiple code paths. The format of the entry can be
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found in the documentation found at the
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<a href="http://valgrind.org/">Valgrind home page</a>.
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The following trace was added to <code>tests/.valgrind.supp</code>
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in order to suppress the warning:
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</p>
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<pre>
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{
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dlInitMemoryLeak1
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Memcheck:Leak
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fun:?alloc
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...
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fun:call_init.part.0
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fun:_dl_init
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...
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obj:*/lib*/ld-2.*so*
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}
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</pre>
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</li>
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<li>Update tests and/or documentation, particularly if you are adding
|
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a new feature or changing the output of a program.</li>
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</ol>
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<p>
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There is more on this subject, including lots of links to background
|
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reading on the subject, on
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<a href="http://et.redhat.com/~rjones/how-to-supply-code-to-open-source-projects/">
|
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Richard Jones' guide to working with open source projects</a>.
|
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</p>
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|
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<h2><a name="indent">Code indentation</a></h2>
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<p>
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Libvirt's C source code generally adheres to some basic code-formatting
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conventions. The existing code base is not totally consistent on this
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front, but we do prefer that contributed code be formatted similarly.
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In short, use spaces-not-TABs for indentation, use 4 spaces for each
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indentation level, and other than that, follow the K&R style.
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</p>
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<p>
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If you use Emacs, add the following to one of one of your start-up files
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(e.g., ~/.emacs), to help ensure that you get indentation right:
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</p>
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<pre>
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;;; When editing C sources in libvirt, use this style.
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(defun libvirt-c-mode ()
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"C mode with adjusted defaults for use with libvirt."
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(interactive)
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(c-set-style "K&R")
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(setq indent-tabs-mode nil) ; indent using spaces, not TABs
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(setq c-indent-level 4)
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(setq c-basic-offset 4))
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(add-hook 'c-mode-hook
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'(lambda () (if (string-match "/libvirt" (buffer-file-name))
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(libvirt-c-mode))))
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</pre>
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<p>
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If you use vim, append the following to your ~/.vimrc file:
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</p>
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<pre>
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set nocompatible
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filetype on
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set autoindent
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set smartindent
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set cindent
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set tabstop=8
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set shiftwidth=4
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set expandtab
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set cinoptions=(0,:0,l1,t0
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filetype plugin indent on
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au FileType make setlocal noexpandtab
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au BufRead,BufNewFile *.am setlocal noexpandtab
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match ErrorMsg /\s\+$\| \+\ze\t/
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</pre>
|
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<p>
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Or if you don't want to mess your ~/.vimrc up, you can save the above
|
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into a file called .lvimrc (not .vimrc) located at the root of libvirt
|
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source, then install a vim script from
|
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http://www.vim.org/scripts/script.php?script_id=1408,
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which will load the .lvimrc only when you edit libvirt code.
|
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</p>
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<h2><a name="formatting">Code formatting (especially for new code)</a></h2>
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<p>
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With new code, we can be even more strict.
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Please apply the following function (using GNU indent) to any new code.
|
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Note that this also gives you an idea of the type of spacing we prefer
|
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around operators and keywords:
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</p>
|
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|
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<pre>
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indent-libvirt()
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{
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indent -bad -bap -bbb -bli4 -br -ce -brs -cs -i4 -l75 -lc75 \
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-sbi4 -psl -saf -sai -saw -sbi4 -ss -sc -cdw -cli4 -npcs -nbc \
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--no-tabs "$@"
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}
|
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</pre>
|
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|
|
<p>
|
|
Note that sometimes you'll have to post-process that output further, by
|
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piping it through <code>expand -i</code>, since some leading TABs can get through.
|
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Usually they're in macro definitions or strings, and should be converted
|
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anyhow.
|
|
</p>
|
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|
|
<p>
|
|
Libvirt requires a C99 compiler for various reasons. However,
|
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most of the code base prefers to stick to C89 syntax unless
|
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there is a compelling reason otherwise. For example, it is
|
|
preferable to use <code>/* */</code> comments rather
|
|
than <code>//</code>. Also, when declaring local variables, the
|
|
prevailing style has been to declare them at the beginning of a
|
|
scope, rather than immediately before use.
|
|
</p>
|
|
|
|
|
|
<h2><a name="bracket_spacing">Bracket spacing</a></h2>
|
|
|
|
<p>
|
|
The keywords <code>if</code>, <code>for</code>, <code>while</code>,
|
|
and <code>switch</code> must have a single space following them
|
|
before the opening bracket. E.g.
|
|
</p>
|
|
<pre>
|
|
if(foo) // Bad
|
|
if (foo) // Good
|
|
</pre>
|
|
|
|
<p>
|
|
Function implementations must <strong>not</strong> have any whitespace
|
|
between the function name and the opening bracket. E.g.
|
|
</p>
|
|
<pre>
|
|
int foo (int wizz) // Bad
|
|
int foo(int wizz) // Good
|
|
</pre>
|
|
|
|
<p>
|
|
Function calls must <strong>not</strong> have any whitespace
|
|
between the function name and the opening bracket. E.g.
|
|
</p>
|
|
<pre>
|
|
bar = foo (wizz); // Bad
|
|
bar = foo(wizz); // Good
|
|
</pre>
|
|
|
|
<p>
|
|
Function typedefs must <strong>not</strong> have any whitespace
|
|
between the closing bracket of the function name and opening
|
|
bracket of the arg list. E.g.
|
|
</p>
|
|
<pre>
|
|
typedef int (*foo) (int wizz); // Bad
|
|
typedef int (*foo)(int wizz); // Good
|
|
</pre>
|
|
|
|
<p>
|
|
There must not be any whitespace immediately following any
|
|
opening bracket, or immediately prior to any closing bracket. E.g.
|
|
</p>
|
|
<pre>
|
|
int foo( int wizz ); // Bad
|
|
int foo(int wizz); // Good
|
|
</pre>
|
|
|
|
<h2><a name="comma">Commas</a></h2>
|
|
|
|
<p>
|
|
Commas should always be followed by a space or end of line, and
|
|
never have leading space; this is enforced during 'make
|
|
syntax-check'.
|
|
</p>
|
|
<pre>
|
|
call(a,b ,c);// Bad
|
|
call(a, b, c); // Good
|
|
</pre>
|
|
|
|
<p>
|
|
When declaring an enum or using a struct initializer that
|
|
occupies more than one line, use a trailing comma. That way,
|
|
future edits to extend the list only have to add a line, rather
|
|
than modify an existing line to add the intermediate comma. Any
|
|
sentinel enumerator value with a name ending in _LAST is exempt,
|
|
since you would extend such an enum before the _LAST element.
|
|
Another reason to favor trailing commas is that it requires less
|
|
effort to produce via code generators. Note that the syntax
|
|
checker is unable to enforce a style of trailing commas, so
|
|
there are counterexamples in existing code which do not use it;
|
|
also, while C99 allows trailing commas, remember that JSON and
|
|
XDR do not.
|
|
</p>
|
|
<pre>
|
|
enum {
|
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VALUE_ONE,
|
|
VALUE_TWO // Bad
|
|
};
|
|
enum {
|
|
VALUE_THREE,
|
|
VALUE_FOUR, // Good
|
|
};
|
|
</pre>
|
|
|
|
<h2><a name="semicolon">Semicolons</a></h2>
|
|
|
|
<p>
|
|
Semicolons should never have a space beforehand. Inside the
|
|
condition of a <code>for</code> loop, there should always be a
|
|
space or line break after each semicolon, except for the special
|
|
case of an infinite loop (although more infinite loops
|
|
use <code>while</code>). While not enforced, loop counters
|
|
generally use post-increment.
|
|
</p>
|
|
<pre>
|
|
for (i = 0 ;i < limit ; ++i) { // Bad
|
|
for (i = 0; i < limit; i++) { // Good
|
|
for (;;) { // ok
|
|
while (1) { // Better
|
|
</pre>
|
|
<p>
|
|
Empty loop bodies are better represented with curly braces and a
|
|
comment, although use of a semicolon is not currently rejected.
|
|
</p>
|
|
<pre>
|
|
while ((rc = waitpid(pid, &st, 0) == -1) &&
|
|
errno == EINTR); // ok
|
|
while ((rc = waitpid(pid, &st, 0) == -1) &&
|
|
errno == EINTR) { // Better
|
|
/* nothing */
|
|
}
|
|
</pre>
|
|
|
|
<h2><a name="curly_braces">Curly braces</a></h2>
|
|
|
|
<p>
|
|
Omit the curly braces around an <code>if</code>, <code>while</code>,
|
|
<code>for</code> etc. body only
|
|
when that body occupies a single line. In every other case we require
|
|
the braces. This ensures that it is trivially easy to identify a
|
|
single-<i>statement</i> loop: each has only one <i>line</i> in its body.
|
|
</p>
|
|
<p>
|
|
Omitting braces with a single-line body is fine:
|
|
</p>
|
|
|
|
<pre>
|
|
while (expr) // one-line body -> omitting curly braces is ok
|
|
single_line_stmt();
|
|
</pre>
|
|
|
|
<p>
|
|
However, the moment your loop/if/else body extends on to a second
|
|
line, for whatever reason (even if it's just an added comment), then
|
|
you should add braces. Otherwise, it would be too easy to insert a
|
|
statement just before that comment (without adding braces), thinking
|
|
it is already a multi-statement loop:
|
|
</p>
|
|
|
|
<pre>
|
|
while (true) // BAD! multi-line body with no braces
|
|
/* comment... */
|
|
single_line_stmt();
|
|
</pre>
|
|
<p>
|
|
Do this instead:
|
|
</p>
|
|
<pre>
|
|
while (true) { // Always put braces around a multi-line body.
|
|
/* comment... */
|
|
single_line_stmt();
|
|
}
|
|
</pre>
|
|
<p>
|
|
There is one exception: when the second body line is not at the same
|
|
indentation level as the first body line:
|
|
</p>
|
|
<pre>
|
|
if (expr)
|
|
die("a diagnostic that would make this line"
|
|
" extend past the 80-column limit"));
|
|
</pre>
|
|
|
|
<p>
|
|
It is safe to omit the braces in the code above, since the
|
|
further-indented second body line makes it obvious that this is still
|
|
a single-statement body.
|
|
</p>
|
|
|
|
<p>
|
|
To reiterate, don't do this:
|
|
</p>
|
|
|
|
<pre>
|
|
if (expr) // BAD: no braces around...
|
|
while (expr_2) { // ... a multi-line body
|
|
...
|
|
}
|
|
</pre>
|
|
|
|
<p>
|
|
Do this, instead:
|
|
</p>
|
|
|
|
<pre>
|
|
if (expr) {
|
|
while (expr_2) {
|
|
...
|
|
}
|
|
}
|
|
</pre>
|
|
|
|
<p>
|
|
However, there is one exception in the other direction, when even a
|
|
one-line block should have braces. That occurs when that one-line,
|
|
brace-less block is an <code>if</code> or <code>else</code>
|
|
block, and the counterpart block <b>does</b> use braces. In
|
|
that case, put braces around both blocks. Also, if
|
|
the <code>else</code> block is much shorter than
|
|
the <code>if</code> block, consider negating the
|
|
<code>if</code>-condition and swapping the bodies, putting the
|
|
short block first and making the longer, multi-line block be the
|
|
<code>else</code> block.
|
|
</p>
|
|
|
|
<pre>
|
|
if (expr) {
|
|
...
|
|
...
|
|
}
|
|
else
|
|
x = y; // BAD: braceless "else" with braced "then",
|
|
// and short block last
|
|
|
|
if (expr)
|
|
x = y; // BAD: braceless "if" with braced "else"
|
|
else {
|
|
...
|
|
...
|
|
}
|
|
</pre>
|
|
|
|
<p>
|
|
Keeping braces consistent and putting the short block first is
|
|
preferred, especially when the multi-line body is more than a
|
|
few lines long, because it is easier to read and grasp the semantics of
|
|
an if-then-else block when the simpler block occurs first, rather than
|
|
after the more involved block:
|
|
</p>
|
|
|
|
<pre>
|
|
if (!expr) {
|
|
x = y; // putting the smaller block first is more readable
|
|
} else {
|
|
...
|
|
...
|
|
}
|
|
</pre>
|
|
|
|
<p>
|
|
But if negating a complex condition is too ugly, then at least
|
|
add braces:
|
|
</p>
|
|
|
|
<pre>
|
|
if (complex expr not worth negating) {
|
|
...
|
|
...
|
|
} else {
|
|
x = y;
|
|
}
|
|
</pre>
|
|
|
|
<h2><a name="preprocessor">Preprocessor</a></h2>
|
|
|
|
<p>Macros defined with an ALL_CAPS name should generally be
|
|
assumed to be unsafe with regards to arguments with side-effects
|
|
(that is, MAX(a++, b--) might increment a or decrement b too
|
|
many or too few times). Exceptions to this rule are explicitly
|
|
documented for macros in viralloc.h and virstring.h.
|
|
</p>
|
|
|
|
<p>
|
|
For variadic macros, stick with C99 syntax:
|
|
</p>
|
|
<pre>
|
|
#define vshPrint(_ctl, ...) fprintf(stdout, __VA_ARGS__)
|
|
</pre>
|
|
|
|
<p>Use parenthesis when checking if a macro is defined, and use
|
|
indentation to track nesting:
|
|
</p>
|
|
<pre>
|
|
#if defined(HAVE_POSIX_FALLOCATE) && !defined(HAVE_FALLOCATE)
|
|
# define fallocate(a,ignored,b,c) posix_fallocate(a,b,c)
|
|
#endif
|
|
</pre>
|
|
|
|
<h2><a name="types">C types</a></h2>
|
|
|
|
<p>
|
|
Use the right type.
|
|
</p>
|
|
|
|
<h3>Scalars</h3>
|
|
|
|
<ul>
|
|
<li>If you're using <code>int</code> or <code>long</code>, odds are
|
|
good that there's a better type.</li>
|
|
<li>If a variable is counting something, be sure to declare it with an
|
|
unsigned type.</li>
|
|
<li>If it's memory-size-related, use <code>size_t</code> (use
|
|
<code>ssize_t</code> only if required).</li>
|
|
<li>If it's file-size related, use uintmax_t, or maybe <code>off_t</code>.</li>
|
|
<li>If it's file-offset related (i.e., signed), use <code>off_t</code>.</li>
|
|
<li>If it's just counting small numbers use <code>unsigned int</code>;
|
|
(on all but oddball embedded systems, you can assume that that
|
|
type is at least four bytes wide).</li>
|
|
<li>If a variable has boolean semantics, give it the <code>bool</code> type
|
|
and use the corresponding <code>true</code> and <code>false</code> macros.
|
|
It's ok to include <stdbool.h>, since libvirt's use of gnulib ensures
|
|
that it exists and is usable.</li>
|
|
<li>In the unusual event that you require a specific width, use a
|
|
standard type like <code>int32_t</code>, <code>uint32_t</code>,
|
|
<code>uint64_t</code>, etc.</li>
|
|
<li>While using <code>bool</code> is good for readability, it comes with
|
|
minor caveats:
|
|
<ul>
|
|
<li>Don't use <code>bool</code> in places where the type size must be constant across
|
|
all systems, like public interfaces and on-the-wire protocols. Note
|
|
that it would be possible (albeit wasteful) to use <code>bool</code> in libvirt's
|
|
logical wire protocol, since XDR maps that to its lower-level <code>bool_t</code>
|
|
type, which <b>is</b> fixed-size.</li>
|
|
<li>Don't compare a bool variable against the literal, <code>true</code>,
|
|
since a value with a logical non-false value need not be <code>1</code>.
|
|
I.e., don't write <code>if (seen == true) ...</code>. Rather,
|
|
write <code>if (seen)...</code>.</li>
|
|
</ul>
|
|
</li>
|
|
</ul>
|
|
|
|
<p>
|
|
Of course, take all of the above with a grain of salt. If you're about
|
|
to use some system interface that requires a type like <code>size_t</code>,
|
|
<code>pid_t</code> or <code>off_t</code>, use matching types for any
|
|
corresponding variables.
|
|
</p>
|
|
|
|
<p>
|
|
Also, if you try to use e.g., <code>unsigned int</code> as a type, and that
|
|
conflicts with the signedness of a related variable, sometimes
|
|
it's best just to use the <b>wrong</b> type, if <i>pulling the thread</i>
|
|
and fixing all related variables would be too invasive.
|
|
</p>
|
|
|
|
<p>
|
|
Finally, while using descriptive types is important, be careful not to
|
|
go overboard. If whatever you're doing causes warnings, or requires
|
|
casts, then reconsider or ask for help.
|
|
</p>
|
|
|
|
<h3>Pointers</h3>
|
|
|
|
<p>
|
|
Ensure that all of your pointers are <i>const-correct</i>.
|
|
Unless a pointer is used to modify the pointed-to storage,
|
|
give it the <code>const</code> attribute. That way, the reader knows
|
|
up-front that this is a read-only pointer. Perhaps more
|
|
importantly, if we're diligent about this, when you see a non-const
|
|
pointer, you're guaranteed that it is used to modify the storage
|
|
it points to, or it is aliased to another pointer that is.
|
|
</p>
|
|
|
|
<h2><a name="memalloc">Low level memory management</a></h2>
|
|
|
|
<p>
|
|
Use of the malloc/free/realloc/calloc APIs is deprecated in the libvirt
|
|
codebase, because they encourage a number of serious coding bugs and do
|
|
not enable compile time verification of checks for NULL. Instead of these
|
|
routines, use the macros from viralloc.h.
|
|
</p>
|
|
|
|
<ul>
|
|
<li><p>To allocate a single object:</p>
|
|
|
|
<pre>
|
|
virDomainPtr domain;
|
|
|
|
if (VIR_ALLOC(domain) < 0)
|
|
return NULL;
|
|
</pre>
|
|
</li>
|
|
|
|
<li><p>To allocate an array of objects:</p>
|
|
<pre>
|
|
virDomainPtr domains;
|
|
size_t ndomains = 10;
|
|
|
|
if (VIR_ALLOC_N(domains, ndomains) < 0)
|
|
return NULL;
|
|
</pre>
|
|
</li>
|
|
|
|
<li><p>To allocate an array of object pointers:</p>
|
|
<pre>
|
|
virDomainPtr *domains;
|
|
size_t ndomains = 10;
|
|
|
|
if (VIR_ALLOC_N(domains, ndomains) < 0)
|
|
return NULL;
|
|
</pre>
|
|
</li>
|
|
|
|
<li><p>To re-allocate the array of domains to be 1 element
|
|
longer (however, note that repeatedly expanding an array by 1
|
|
scales quadratically, so this is recommended only for smaller
|
|
arrays):</p>
|
|
<pre>
|
|
virDomainPtr domains;
|
|
size_t ndomains = 0;
|
|
|
|
if (VIR_EXPAND_N(domains, ndomains, 1) < 0)
|
|
return NULL;
|
|
domains[ndomains - 1] = domain;
|
|
</pre></li>
|
|
|
|
<li><p>To ensure an array has room to hold at least one more
|
|
element (this approach scales better, but requires tracking
|
|
allocation separately from usage)</p>
|
|
|
|
<pre>
|
|
virDomainPtr domains;
|
|
size_t ndomains = 0;
|
|
size_t ndomains_max = 0;
|
|
|
|
if (VIR_RESIZE_N(domains, ndomains_max, ndomains, 1) < 0)
|
|
return NULL;
|
|
domains[ndomains++] = domain;
|
|
</pre>
|
|
</li>
|
|
|
|
<li><p>To trim an array of domains from its allocated size down
|
|
to the actual used size:</p>
|
|
|
|
<pre>
|
|
virDomainPtr domains;
|
|
size_t ndomains = x;
|
|
size_t ndomains_max = y;
|
|
|
|
VIR_SHRINK_N(domains, ndomains_max, ndomains_max - ndomains);
|
|
</pre></li>
|
|
|
|
<li><p>To free an array of domains:</p>
|
|
<pre>
|
|
virDomainPtr domains;
|
|
size_t ndomains = x;
|
|
size_t ndomains_max = y;
|
|
size_t i;
|
|
|
|
for (i = 0; i < ndomains; i++)
|
|
VIR_FREE(domains[i]);
|
|
VIR_FREE(domains);
|
|
ndomains_max = ndomains = 0;
|
|
</pre>
|
|
</li>
|
|
</ul>
|
|
|
|
<h2><a name="file_handling">File handling</a></h2>
|
|
|
|
<p>
|
|
Usage of the <code>fdopen()</code>, <code>close()</code>, <code>fclose()</code>
|
|
APIs is deprecated in libvirt code base to help avoiding double-closing of files
|
|
or file descriptors, which is particularly dangerous in a multi-threaded
|
|
application. Instead of these APIs, use the macros from virfile.h
|
|
</p>
|
|
|
|
<ul>
|
|
<li><p>Open a file from a file descriptor:</p>
|
|
|
|
<pre>
|
|
if ((file = VIR_FDOPEN(fd, "r")) == NULL) {
|
|
virReportSystemError(errno, "%s",
|
|
_("failed to open file from file descriptor"));
|
|
return -1;
|
|
}
|
|
/* fd is now invalid; only access the file using file variable */
|
|
</pre></li>
|
|
|
|
<li><p>Close a file descriptor:</p>
|
|
<pre>
|
|
if (VIR_CLOSE(fd) < 0) {
|
|
virReportSystemError(errno, "%s", _("failed to close file"));
|
|
}
|
|
</pre></li>
|
|
|
|
<li><p>Close a file:</p>
|
|
|
|
<pre>
|
|
if (VIR_FCLOSE(file) < 0) {
|
|
virReportSystemError(errno, "%s", _("failed to close file"));
|
|
}
|
|
</pre></li>
|
|
|
|
<li><p>Close a file or file descriptor in an error path, without losing
|
|
the previous <code>errno</code> value:</p>
|
|
|
|
<pre>
|
|
VIR_FORCE_CLOSE(fd);
|
|
VIR_FORCE_FCLOSE(file);
|
|
</pre>
|
|
</li>
|
|
</ul>
|
|
|
|
<h2><a name="string_comparision">String comparisons</a></h2>
|
|
|
|
<p>
|
|
Do not use the strcmp, strncmp, etc functions directly. Instead use
|
|
one of the following semantically named macros
|
|
</p>
|
|
|
|
<ul>
|
|
<li><p>For strict equality:</p>
|
|
<pre>
|
|
STREQ(a,b)
|
|
STRNEQ(a,b)
|
|
</pre>
|
|
</li>
|
|
|
|
<li><p>For case insensitive equality:</p>
|
|
<pre>
|
|
STRCASEEQ(a,b)
|
|
STRCASENEQ(a,b)
|
|
</pre>
|
|
</li>
|
|
|
|
<li><p>For strict equality of a substring:</p>
|
|
<pre>
|
|
STREQLEN(a,b,n)
|
|
STRNEQLEN(a,b,n)
|
|
</pre>
|
|
</li>
|
|
|
|
<li><p>For case insensitive equality of a substring:</p>
|
|
<pre>
|
|
STRCASEEQLEN(a,b,n)
|
|
STRCASENEQLEN(a,b,n)
|
|
</pre>
|
|
</li>
|
|
|
|
<li><p>For strict equality of a prefix:</p>
|
|
<pre>
|
|
STRPREFIX(a,b)
|
|
</pre>
|
|
</li>
|
|
<li><p>To avoid having to check if a or b are NULL:</p>
|
|
<pre>
|
|
STREQ_NULLABLE(a, b)
|
|
STRNEQ_NULLABLE(a, b)
|
|
</pre>
|
|
</li>
|
|
</ul>
|
|
|
|
|
|
<h2><a name="string_copying">String copying</a></h2>
|
|
|
|
<p>
|
|
Do not use the strncpy function. According to the man page, it
|
|
does <b>not</b> guarantee a NULL-terminated buffer, which makes
|
|
it extremely dangerous to use. Instead, use one of the
|
|
functionally equivalent functions:
|
|
</p>
|
|
|
|
<pre>
|
|
virStrncpy(char *dest, const char *src, size_t n, size_t destbytes)
|
|
</pre>
|
|
<p>
|
|
The first three arguments have the same meaning as for strncpy;
|
|
namely the destination, source, and number of bytes to copy,
|
|
respectively. The last argument is the number of bytes
|
|
available in the destination string; if a copy of the source
|
|
string (including a \0) will not fit into the destination, no
|
|
bytes are copied and the routine returns NULL. Otherwise, n
|
|
bytes from the source are copied into the destination and a
|
|
trailing \0 is appended.
|
|
</p>
|
|
|
|
<pre>
|
|
virStrcpy(char *dest, const char *src, size_t destbytes)
|
|
</pre>
|
|
<p>
|
|
Use this variant if you know you want to copy the entire src
|
|
string into dest. Note that this is a macro, so arguments could
|
|
be evaluated more than once. This is equivalent to
|
|
virStrncpy(dest, src, strlen(src), destbytes)
|
|
</p>
|
|
|
|
<pre>
|
|
virStrcpyStatic(char *dest, const char *src)
|
|
</pre>
|
|
<p>
|
|
Use this variant if you know you want to copy the entire src
|
|
string into dest <b>and</b> you know that your destination string is
|
|
a static string (i.e. that sizeof(dest) returns something
|
|
meaningful). Note that this is a macro, so arguments could be
|
|
evaluated more than once. This is equivalent to
|
|
virStrncpy(dest, src, strlen(src), sizeof(dest)).
|
|
</p>
|
|
|
|
<pre>
|
|
VIR_STRDUP(char *dst, const char *src);
|
|
VIR_STRNDUP(char *dst, const char *src, size_t n);
|
|
</pre>
|
|
<p>
|
|
You should avoid using strdup or strndup directly as they do not report
|
|
out-of-memory error, and do not allow a NULL source. Use
|
|
VIR_STRDUP or VIR_STRNDUP macros instead, which return 0 for
|
|
NULL source, 1 for successful copy, and -1 for allocation
|
|
failure with the error already reported. In very
|
|
specific cases, when you don't want to report the out-of-memory error, you
|
|
can use VIR_STRDUP_QUIET or VIR_STRNDUP_QUIET, but such usage is very rare
|
|
and usually considered a flaw.
|
|
</p>
|
|
|
|
<h2><a name="strbuf">Variable length string buffer</a></h2>
|
|
|
|
<p>
|
|
If there is a need for complex string concatenations, avoid using
|
|
the usual sequence of malloc/strcpy/strcat/snprintf functions and
|
|
make use of the virBuffer API described in buf.h
|
|
</p>
|
|
|
|
<p>Typical usage is as follows:</p>
|
|
|
|
<pre>
|
|
char *
|
|
somefunction(...)
|
|
{
|
|
virBuffer buf = VIR_BUFFER_INITIALIZER;
|
|
|
|
...
|
|
|
|
virBufferAddLit(&buf, "<domain>\n");
|
|
virBufferAsprintf(&buf, " <memory>%d</memory>\n", memory);
|
|
...
|
|
virBufferAddLit(&buf, "</domain>\n");
|
|
|
|
...
|
|
|
|
if (virBufferError(&buf)) {
|
|
virBufferFreeAndReset(&buf);
|
|
virReportOOMError();
|
|
return NULL;
|
|
}
|
|
|
|
return virBufferContentAndReset(&buf);
|
|
}
|
|
</pre>
|
|
|
|
|
|
<h2><a name="includes">Include files</a></h2>
|
|
|
|
<p>
|
|
There are now quite a large number of include files, both libvirt
|
|
internal and external, and system includes. To manage all this
|
|
complexity it's best to stick to the following general plan for all
|
|
*.c source files:
|
|
</p>
|
|
|
|
<pre>
|
|
/*
|
|
* Copyright notice
|
|
* ....
|
|
* ....
|
|
* ....
|
|
*
|
|
*/
|
|
|
|
#include <config.h> Must come first in every file.
|
|
|
|
#include <stdio.h> Any system includes you need.
|
|
#include <string.h>
|
|
#include <limits.h>
|
|
|
|
#if WITH_NUMACTL Some system includes aren't supported
|
|
# include <numa.h> everywhere so need these #if guards.
|
|
#endif
|
|
|
|
#include "internal.h" Include this first, after system includes.
|
|
|
|
#include "util.h" Any libvirt internal header files.
|
|
#include "buf.h"
|
|
|
|
static int
|
|
myInternalFunc() The actual code.
|
|
{
|
|
...
|
|
</pre>
|
|
|
|
<p>
|
|
Of particular note: <b>Do not</b> include libvirt/libvirt.h,
|
|
libvirt/virterror.h, libvirt/libvirt-qemu.h, or libvirt/libvirt-lxc.h.
|
|
They are included by "internal.h" already and there are some special reasons
|
|
why you cannot include these files explicitly. One of the special cases,
|
|
"libvirt/libvirt.h" is included prior to "internal.h" in "remote_protocol.x",
|
|
to avoid exposing *_LAST enum elements.
|
|
</p>
|
|
|
|
|
|
<h2><a name="printf">Printf-style functions</a></h2>
|
|
|
|
<p>
|
|
Whenever you add a new printf-style function, i.e., one with a format
|
|
string argument and following "..." in its prototype, be sure to use
|
|
gcc's printf attribute directive in the prototype. For example, here's
|
|
the one for virAsprintf, in util.h:
|
|
</p>
|
|
|
|
<pre>
|
|
int virAsprintf(char **strp, const char *fmt, ...)
|
|
ATTRIBUTE_FORMAT(printf, 2, 3);
|
|
</pre>
|
|
|
|
<p>
|
|
This makes it so gcc's -Wformat and -Wformat-security options can do
|
|
their jobs and cross-check format strings with the number and types
|
|
of arguments.
|
|
</p>
|
|
|
|
<p>
|
|
When printing to a string, consider using virBuffer for
|
|
incremental allocations, virAsprintf for a one-shot allocation,
|
|
and snprintf for fixed-width buffers. Do not use sprintf, even
|
|
if you can prove the buffer won't overflow, since gnulib does
|
|
not provide the same portability guarantees for sprintf as it
|
|
does for snprintf.
|
|
</p>
|
|
|
|
<h2><a name="goto">Use of goto</a></h2>
|
|
|
|
<p>
|
|
The use of goto is not forbidden, and goto is widely used
|
|
throughout libvirt. While the uncontrolled use of goto will
|
|
quickly lead to unmaintainable code, there is a place for it in
|
|
well structured code where its use increases readability and
|
|
maintainability. In general, if goto is used for error
|
|
recovery, it's likely to be ok, otherwise, be cautious or avoid
|
|
it all together.
|
|
</p>
|
|
|
|
<p>
|
|
The typical use of goto is to jump to cleanup code in the case
|
|
of a long list of actions, any of which may fail and cause the
|
|
entire operation to fail. In this case, a function will have a
|
|
single label at the end of the function. It's almost always ok
|
|
to use this style. In particular, if the cleanup code only
|
|
involves free'ing memory, then having multiple labels is
|
|
overkill. VIR_FREE() and every function named XXXFree() in
|
|
libvirt is required to handle NULL as its arg. Thus you can
|
|
safely call free on all the variables even if they were not yet
|
|
allocated (yes they have to have been initialized to NULL).
|
|
This is much simpler and clearer than having multiple labels.
|
|
</p>
|
|
|
|
<p>
|
|
There are a couple of signs that a particular use of goto is not
|
|
ok:
|
|
</p>
|
|
|
|
<ul>
|
|
<li>You're using multiple labels. If you find yourself using
|
|
multiple labels, you're strongly encouraged to rework your code
|
|
to eliminate all but one of them.</li>
|
|
<li>The goto jumps back up to a point above the current line of
|
|
code being executed. Please use some combination of looping
|
|
constructs to re-execute code instead; it's almost certainly
|
|
going to be more understandable by others. One well-known
|
|
exception to this rule is restarting an i/o operation following
|
|
EINTR.</li>
|
|
<li>The goto jumps down to an arbitrary place in the middle of a
|
|
function followed by further potentially failing calls. You
|
|
should almost certainly be using a conditional and a block
|
|
instead of a goto. Perhaps some of your function's logic would
|
|
be better pulled out into a helper function.</li>
|
|
</ul>
|
|
|
|
<p>
|
|
Although libvirt does not encourage the Linux kernel wind/unwind
|
|
style of multiple labels, there's a good general discussion of
|
|
the issue archived at
|
|
<a href="http://kerneltrap.org/node/553/2131">KernelTrap</a>
|
|
</p>
|
|
|
|
<p>
|
|
When using goto, please use one of these standard labels if it
|
|
makes sense:
|
|
</p>
|
|
|
|
<pre>
|
|
error: A path only taken upon return with an error code
|
|
cleanup: A path taken upon return with success code + optional error
|
|
no_memory: A path only taken upon return with an OOM error code
|
|
retry: If needing to jump upwards (e.g., retry on EINTR)
|
|
</pre>
|
|
|
|
|
|
|
|
<h2><a name="committers">Libvirt committer guidelines</a></h2>
|
|
|
|
<p>
|
|
The AUTHORS files indicates the list of people with commit access right
|
|
who can actually merge the patches.
|
|
</p>
|
|
|
|
<p>
|
|
The general rule for committing a patch is to make sure
|
|
it has been reviewed
|
|
properly in the mailing-list first, usually if a couple of people gave an
|
|
ACK or +1 to a patch and nobody raised an objection on the list it should
|
|
be good to go. If the patch touches a part of the code where you're not
|
|
the main maintainer, or where you do not have a very clear idea of
|
|
how things work, it's better
|
|
to wait for a more authoritative feedback though. Before committing, please
|
|
also rebuild locally, run 'make check syntax-check', and make sure you
|
|
don't raise errors. Try to look for warnings too; for example,
|
|
configure with
|
|
</p>
|
|
<pre>
|
|
--enable-compile-warnings=error
|
|
</pre>
|
|
<p>
|
|
which adds -Werror to compile flags, so no warnings get missed
|
|
</p>
|
|
|
|
<p>
|
|
An exception to 'review and approval on the list first' is fixing failures
|
|
to build:
|
|
</p>
|
|
<ul>
|
|
<li>if a recently committed patch breaks compilation on a platform
|
|
or for a given driver, then it's fine to commit a minimal fix
|
|
directly without getting the review feedback first</li>
|
|
<li>if make check or make syntax-check breaks, if there is
|
|
an obvious fix, it's fine to commit immediately.
|
|
The patch should still be sent to the list (or tell what the fix was if
|
|
trivial), and 'make check syntax-check' should pass too, before committing
|
|
anything</li>
|
|
<li>
|
|
fixes for documentation and code comments can be managed
|
|
in the same way, but still make sure they get reviewed if non-trivial.
|
|
</li>
|
|
</ul>
|
|
</body>
|
|
</html>
|