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582 lines
19 KiB
HTML
582 lines
19 KiB
HTML
<html>
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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. A command similar to this
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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></li>
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<li>Split large changes into a series of smaller patches, self-contained
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if possible, with an explanation of each patch and an explanation of how
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the sequence of patches fits together.</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 -Werror:</p>
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<pre>
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./configure --enable-compile-warnings=error
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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>
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The latter test checks for memory leaks.
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</p>
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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</pre>
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<p>
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Also, individual tests can be run from inside the 'tests/'
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directory, like:
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</p>
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<pre>
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./qemuxml2xmltest</pre>
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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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<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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<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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<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>
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Note that sometimes you'll have to post-process that output further, by
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piping it through "expand -i", 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.
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</p>
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<h2><a href="types">Preprocessor</a></h2>
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<p>
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For variadic macros, stick with C99 syntax:
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</p>
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<pre>
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#define vshPrint(_ctl, ...) fprintf(stdout, __VA_ARGS__)
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</pre>
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<p>Use parenthesis when checking if a macro is defined, and use
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indentation to track nesting:
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</p>
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<pre>
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#if defined(HAVE_POSIX_FALLOCATE) && !defined(HAVE_FALLOCATE)
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# define fallocate(a,ignored,b,c) posix_fallocate(a,b,c)
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#endif
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</pre>
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<h2><a href="types">C types</a></h2>
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<p>
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Use the right type.
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</p>
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<h3>Scalars</h3>
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<ul>
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<li>If you're using "int" or "long", odds are good that there's a better type.</li>
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<li>If a variable is counting something, be sure to declare it with an
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unsigned type.</li>
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<li>If it's memory-size-related, use size_t (use ssize_t only if required).</li>
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<li>If it's file-size related, use uintmax_t, or maybe off_t.</li>
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<li>If it's file-offset related (i.e., signed), use off_t.</li>
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<li>If it's just counting small numbers use "unsigned int";
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(on all but oddball embedded systems, you can assume that that
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type is at least four bytes wide).</li>
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<li>If a variable has boolean semantics, give it the "bool" type
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and use the corresponding "true" and "false" macros. It's ok
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to include <stdbool.h>, since libvirt's use of gnulib ensures
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that it exists and is usable.</li>
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<li>In the unusual event that you require a specific width, use a
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standard type like int32_t, uint32_t, uint64_t, etc.</li>
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<li>While using "bool" is good for readability, it comes with minor caveats:
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<ul>
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<li>Don't use "bool" in places where the type size must be constant across
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all systems, like public interfaces and on-the-wire protocols. Note
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that it would be possible (albeit wasteful) to use "bool" in libvirt's
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logical wire protocol, since XDR maps that to its lower-level bool_t
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type, which *is* fixed-size.</li>
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<li>Don't compare a bool variable against the literal, "true",
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since a value with a logical non-false value need not be "1".
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I.e., don't write "if (seen == true) ...". Rather, write "if (seen)...".</li>
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</ul>
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</li>
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</ul>
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<p>
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Of course, take all of the above with a grain of salt. If you're about
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to use some system interface that requires a type like size_t, pid_t or
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off_t, use matching types for any corresponding variables.
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</p>
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<p>
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Also, if you try to use e.g., "unsigned int" as a type, and that
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conflicts with the signedness of a related variable, sometimes
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it's best just to use the *wrong* type, if "pulling the thread"
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and fixing all related variables would be too invasive.
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</p>
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<p>
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Finally, while using descriptive types is important, be careful not to
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go overboard. If whatever you're doing causes warnings, or requires
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casts, then reconsider or ask for help.
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</p>
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<h3>Pointers</h3>
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<p>
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Ensure that all of your pointers are "const-correct".
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Unless a pointer is used to modify the pointed-to storage,
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give it the "const" attribute. That way, the reader knows
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up-front that this is a read-only pointer. Perhaps more
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importantly, if we're diligent about this, when you see a non-const
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pointer, you're guaranteed that it is used to modify the storage
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it points to, or it is aliased to another pointer that is.
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</p>
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<h2><a name="memalloc">Low level memory management</a></h2>
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<p>
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Use of the malloc/free/realloc/calloc APIs is deprecated in the libvirt
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codebase, because they encourage a number of serious coding bugs and do
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not enable compile time verification of checks for NULL. Instead of these
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routines, use the macros from memory.h
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</p>
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<ul>
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<li><p>eg to allocate a single object:</p>
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<pre>
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virDomainPtr domain;
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if (VIR_ALLOC(domain) < 0) {
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virReportOOMError();
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return NULL;
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}
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</pre></li>
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<li><p>eg to allocate an array of objects</p>
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<pre>
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virDomainPtr domains;
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int ndomains = 10;
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if (VIR_ALLOC_N(domains, ndomains) < 0) {
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virReportOOMError();
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return NULL;
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}
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</pre></li>
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<li><p>eg to allocate an array of object pointers</p>
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<pre>
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virDomainPtr *domains;
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int ndomains = 10;
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if (VIR_ALLOC_N(domains, ndomains) < 0) {
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virReportOOMError();
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return NULL;
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}
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</pre></li>
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<li><p>eg to re-allocate the array of domains to be longer</p>
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<pre>
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ndomains = 20
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if (VIR_REALLOC_N(domains, ndomains) < 0) {
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virReportOOMError();
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return NULL;
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}
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</pre></li>
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<li><p>eg to free the domain</p>
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<pre>
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VIR_FREE(domain);
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</pre></li>
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</ul>
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<h2><a name="string_comparision">String comparisons</a></h2>
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<p>
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Do not use the strcmp, strncmp, etc functions directly. Instead use
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one of the following semantically named macros
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</p>
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<ul>
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<li><p>For strict equality:</p>
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<pre>
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STREQ(a,b)
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STRNEQ(a,b)
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</pre>
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</li>
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<li><p>For case insensitive equality:</p>
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<pre>
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STRCASEEQ(a,b)
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STRCASENEQ(a,b)
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</pre>
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</li>
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<li><p>For strict equality of a substring:</p>
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<pre>
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STREQLEN(a,b,n)
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STRNEQLEN(a,b,n)
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</pre>
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</li>
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<li><p>For case insensitive equality of a substring:</p>
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<pre>
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STRCASEEQLEN(a,b,n)
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STRCASENEQLEN(a,b,n)
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</pre>
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</li>
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<li><p>For strict equality of a prefix:</p>
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<pre>
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STRPREFIX(a,b)
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</pre>
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</li>
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</ul>
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<h2><a name="string_copying">String copying</a></h2>
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<p>
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Do not use the strncpy function. According to the man page, it
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does <b>not</b> guarantee a NULL-terminated buffer, which makes
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it extremely dangerous to use. Instead, use one of the
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functionally equivalent functions:
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</p>
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<pre>virStrncpy(char *dest, const char *src, size_t n, size_t destbytes)</pre>
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<p>
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The first three arguments have the same meaning as for strncpy;
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namely the destination, source, and number of bytes to copy,
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respectively. The last argument is the number of bytes
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available in the destination string; if a copy of the source
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string (including a \0) will not fit into the destination, no
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bytes are copied and the routine returns NULL. Otherwise, n
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bytes from the source are copied into the destination and a
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trailing \0 is appended.
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</p>
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<pre>virStrcpy(char *dest, const char *src, size_t destbytes)</pre>
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<p>
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Use this variant if you know you want to copy the entire src
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string into dest. Note that this is a macro, so arguments could
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be evaluated more than once. This is equivalent to
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virStrncpy(dest, src, strlen(src), destbytes)
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</p>
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<pre>virStrcpyStatic(char *dest, const char *src)</pre>
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<p>
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Use this variant if you know you want to copy the entire src
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string into dest *and* you know that your destination string is
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a static string (i.e. that sizeof(dest) returns something
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meaningful). Note that this is a macro, so arguments could be
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evaluated more than once. This is equivalent to
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virStrncpy(dest, src, strlen(src), sizeof(dest)).
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</p>
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<h2><a name="strbuf">Variable length string buffer</a></h2>
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<p>
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If there is a need for complex string concatenations, avoid using
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the usual sequence of malloc/strcpy/strcat/snprintf functions and
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make use of the virBuffer API described in buf.h
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</p>
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<p>eg typical usage is as follows:</p>
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<pre>
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char *
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somefunction(...) {
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virBuffer buf = VIR_BUFFER_INITIALIZER;
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...
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virBufferAddLit(&buf, "<domain>\n");
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virBufferVSprint(&buf, " <memory>%d</memory>\n", memory);
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...
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virBufferAddLit(&buf, "</domain>\n");
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...
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if (virBufferError(&buf)) {
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virBufferFreeAndReset(&buf);
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virReportOOMError();
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return NULL;
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}
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return virBufferContentAndReset(&buf);
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}
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</pre>
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<h2><a name="includes">Include files</a></h2>
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<p>
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There are now quite a large number of include files, both libvirt
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internal and external, and system includes. To manage all this
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complexity it's best to stick to the following general plan for all
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*.c source files:
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</p>
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<pre>
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/*
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* Copyright notice
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* ....
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* ....
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* ....
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*
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*/
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#include <config.h> Must come first in every file.
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#include <stdio.h> Any system includes you need.
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#include <string.h>
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#include <limits.h>
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#if HAVE_NUMACTL Some system includes aren't supported
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# include <numa.h> everywhere so need these #if guards.
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#endif
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#include "internal.h" Include this first, after system includes.
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#include "util.h" Any libvirt internal header files.
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#include "buf.h"
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static myInternalFunc () The actual code.
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{
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...
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</pre>
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<p>
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Of particular note: *DO NOT* include libvirt/libvirt.h or
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libvirt/virterror.h. It is included by "internal.h" already and there
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are some special reasons why you cannot include these files
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explicitly.
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</p>
|
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|
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<h2><a name="printf">Printf-style functions</a></h2>
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<p>
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Whenever you add a new printf-style function, i.e., one with a format
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string argument and following "..." in its prototype, be sure to use
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gcc's printf attribute directive in the prototype. For example, here's
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the one for virAsprintf, in util.h:
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</p>
|
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|
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<pre>
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int virAsprintf(char **strp, const char *fmt, ...)
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ATTRIBUTE_FORMAT(printf, 2, 3);
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</pre>
|
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<p>
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This makes it so gcc's -Wformat and -Wformat-security options can do
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their jobs and cross-check format strings with the number and types
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of arguments.
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</p>
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|
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<h2><a name="goto">Use of goto</a></h2>
|
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|
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<p>
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The use of goto is not forbidden, and goto is widely used
|
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throughout libvirt. While the uncontrolled use of goto will
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quickly lead to unmaintainable code, there is a place for it in
|
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well structured code where its use increases readability and
|
|
maintainability. In general, if goto is used for error
|
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recovery, it's likely to be ok, otherwise, be cautious or avoid
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it all together.
|
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</p>
|
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<p>
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The typical use of goto is to jump to cleanup code in the case
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of a long list of actions, any of which may fail and cause the
|
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entire operation to fail. In this case, a function will have a
|
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single label at the end of the function. It's almost always ok
|
|
to use this style. In particular, if the cleanup code only
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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
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|
allocated (yes they have to have been initialized to NULL).
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This is much simpler and clearer than having multiple labels.
|
|
</p>
|
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|
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<p>
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There are a couple of signs that a particular use of goto is not
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ok:
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</p>
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<ul>
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<li>You're using multiple labels. If you find yourself using
|
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multiple labels, you're strongly encouraged to rework your code
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to eliminate all but one of them.</li>
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<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
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|
going to be more understandable by others. One well-known
|
|
exception to this rule is restarting an i/o operation following
|
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EINTR.</li>
|
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<li>The goto jumps down to an arbitrary place in the middle of a
|
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function followed by further potentially failing calls. You
|
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should almost certainly be using a conditional and a block
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instead of a goto. Perhaps some of your function's logic would
|
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be better pulled out into a helper function.</li>
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</ul>
|
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|
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<p>
|
|
Although libvirt does not encourage the Linux kernel wind/unwind
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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>
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|
</p>
|
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|
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<p>
|
|
When using goto, please use one of these standard labels if it
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|
makes sense:
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</p>
|
|
|
|
<pre>
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error: A path only taken upon return with an error code
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cleanup: A path taken upon return with success code + optional error
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no_memory: A path only taken upon return with an OOM error code
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retry: If needing to jump upwards (eg retry on EINTR)</pre>
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<h2><a name="committers">Libvirt committer guidelines</a></h2>
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<p>
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The AUTHORS files indicates the list of people with commit access right
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who can actually merge the patches.
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</p>
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<p>
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The general rule for committing a patch is to make sure
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it has been reviewed
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properly in the mailing-list first, usually if a couple of people gave an
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ACK or +1 to a patch and nobody raised an objection on the list it should
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be good to go. If the patch touches a part of the code where you're not
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the main maintainer, or where you do not have a very clear idea of
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how things work, it's better
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to wait for a more authoritative feedback though. Before committing, please
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also rebuild locally, run 'make check syntax-check', and make sure you
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don't raise errors. Try to look for warnings too; for example,
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configure with
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</p>
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<pre>
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--enable-compile-warnings=error
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</pre>
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<p>
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which adds -Werror to compile flags, so no warnings get missed
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</p>
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|
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|
<p>
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An exception to 'review and approval on the list first' is fixing failures
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to build:
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</p>
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<ul>
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<li>if a recently committed patch breaks compilation on a platform
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or for a given driver, then it's fine to commit a minimal fix
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directly without getting the review feedback first</li>
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|
<li>if make check or make syntax-check breaks, if there is
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an obvious fix, it's fine to commit immediately.
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The patch should still be sent to the list (or tell what the fix was if
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|
trivial), and 'make check syntax-check' should pass too, before committing
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anything</li>
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<li>
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fixes for documentation and code comments can be managed
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|
in the same way, but still make sure they get reviewed if non-trivial.
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</li>
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|
</ul>
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</body>
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</html>
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