mirror of
https://gitlab.com/libvirt/libvirt.git
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a3e95abeb5
This documents the following whitespace rules
if(foo) // Bad
if (foo) // Good
int foo (int wizz) // Bad
int foo(int wizz) // Good
bar = foo (wizz); // Bad
bar = foo(wizz); // Good
typedef int (*foo) (int wizz); // Bad
typedef int (*foo)(int wizz); // Good
int foo( int wizz ); // Bad
int foo(int wizz); // Good
There is a syntax-check rule extension to validate all these rules.
Checking for 'function (...args...)' is quite difficult since it
needs to ignore valid usage with keywords like 'if (...test...)'
and while/for/switch. It must also ignore source comments and
quoted strings.
It is not possible todo this with a simple regex in the normal
syntax-check style. So a short Perl script is created instead
to analyse the source. In practice this works well enough. The
only thing it can't cope with is multi-line quoted strings of
the form
"start of string\
more lines\
more line\
the end"
but this can and should be written as
"start of string"
"more lines"
"more line"
"the end"
with this simple change, the bracket checking script does not
have any false positives across libvirt source, provided it
is only run against .c files. It is not practical to run it
against .h files, since those use whitespace extensively to
get alignment (though this is somewhat inconsistent and could
arguably be fixed).
The only limitation is that it cannot detect a violation where
the first arg starts with a '*', eg
foo(*wizz);
since this generates too many false positives on function
typedefs which can't be supressed efficiently.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
970 lines
30 KiB
HTML
970 lines
30 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>
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<p>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>Then, when you want to 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 installion 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>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>
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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
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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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</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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<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\+$\| \+\ze\t/
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</pre>
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<p>
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Or if you don't want to mess your ~/.vimrc up, you can save the above
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into a file called .lvimrc (not .vimrc) located at the root of libvirt
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source, then install a vim script from
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http://www.vim.org/scripts/script.php?script_id=1408,
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which will load the .lvimrc only when you edit libvirt code.
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</p>
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<h2><a name="formatting">Code formatting (especially for new code)</a></h2>
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<p>
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With new code, we can be even more strict.
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Please apply the following function (using GNU indent) to any new code.
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Note that this also gives you an idea of the type of spacing we prefer
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around operators and keywords:
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</p>
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<pre>
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indent-libvirt()
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{
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indent -bad -bap -bbb -bli4 -br -ce -brs -cs -i4 -l75 -lc75 \
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-sbi4 -psl -saf -sai -saw -sbi4 -ss -sc -cdw -cli4 -npcs -nbc \
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--no-tabs "$@"
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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 <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.
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</p>
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<p>
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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
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preferable to use <code>/* */</code> comments rather
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than <code>//</code>. Also, when declaring local variables, the
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prevailing style has been to declare them at the beginning of a
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scope, rather than immediately before use.
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</p>
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<h2><a name="bracket_spacing">Bracket spacing</a></h2>
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<p>
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The keywords <code>if</code>, <code>for</code>, <code>while</code>,
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and <code>switch</code> must have a single space following them
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before the opening bracket. eg
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</p>
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<pre>
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if(foo) // Bad
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if (foo) // Good
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</pre>
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<p>
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Function implementations must <strong>not</strong> have any whitespace
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between the function name and the opening bracket. eg
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</p>
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<pre>
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int foo (int wizz) // Bad
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int foo(int wizz) // Good
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</pre>
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<p>
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Function calls must <strong>not</strong> have any whitespace
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between the function name and the opening bracket. eg
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</p>
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<pre>
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bar = foo (wizz); // Bad
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bar = foo(wizz); // Good
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</pre>
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<p>
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Function typedefs must <strong>not</strong> have any whitespace
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between the closing bracket of the function name and opening
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bracket of the arg list. eg
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</p>
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<pre>
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typedef int (*foo) (int wizz); // Bad
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typedef int (*foo)(int wizz); // Good
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</pre>
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<p>
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There must not be any whitespace immediately following any
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opening bracket, or immediately prior to any closing bracket
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</p>
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<pre>
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int foo( int wizz ); // Bad
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int foo(int wizz); // Good
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</pre>
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<h2><a name="curly_braces">Curly braces</a></h2>
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<p>
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Omit the curly braces around an <code>if</code>, <code>while</code>,
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<code>for</code> etc. body only
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when that body occupies a single line. In every other case we require
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the braces. This ensures that it is trivially easy to identify a
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single-<i>statement</i> loop: each has only one <i>line</i> in its body.
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</p>
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<p>
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Omitting braces with a single-line body is fine:
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</p>
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<pre>
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while (expr) // one-line body -> omitting curly braces is ok
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single_line_stmt();
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</pre>
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<p>
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However, the moment your loop/if/else body extends onto a second
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line, for whatever reason (even if it's just an added comment), then
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you should add braces. Otherwise, it would be too easy to insert a
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statement just before that comment (without adding braces), thinking
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it is already a multi-statement loop:
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</p>
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<pre>
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while (true) // BAD! multi-line body with no braces
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/* comment... */
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single_line_stmt();
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</pre>
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<p>
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Do this instead:
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</p>
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<pre>
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while (true) { // Always put braces around a multi-line body.
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/* comment... */
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single_line_stmt();
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}
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</pre>
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<p>
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There is one exception: when the second body line is not at the same
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indentation level as the first body line:
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</p>
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<pre>
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if (expr)
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die("a diagnostic that would make this line"
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" extend past the 80-column limit"));
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</pre>
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<p>
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It is safe to omit the braces in the code above, since the
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further-indented second body line makes it obvious that this is still
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a single-statement body.
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</p>
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<p>
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To reiterate, don't do this:
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</p>
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<pre>
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if (expr) // BAD: no braces around...
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while (expr_2) { // ... a multi-line body
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...
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}
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</pre>
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<p>
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Do this, instead:
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</p>
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<pre>
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if (expr) {
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while (expr_2) {
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...
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}
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}
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</pre>
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<p>
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However, there is one exception in the other direction, when even a
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one-line block should have braces. That occurs when that one-line,
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brace-less block is an <code>if</code> or <code>else</code>
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block, and the counterpart block <b>does</b> use braces. In
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that case, put braces around both blocks. Also, if
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the <code>else</code> block is much shorter than
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the <code>if</code> block, consider negating the
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<code>if</code>-condition and swapping the bodies, putting the
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short block first and making the longer, multi-line block be the
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<code>else</code> block.
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</p>
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<pre>
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if (expr) {
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...
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...
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}
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else
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x = y; // BAD: braceless "else" with braced "then",
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// and short block last
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if (expr)
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x = y; // BAD: braceless "if" with braced "else"
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else {
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...
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...
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}
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</pre>
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<p>
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Keeping braces consistent and putting the short block first is
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preferred, especially when the multi-line body is more than a
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few lines long, because it is easier to read and grasp the semantics of
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an if-then-else block when the simpler block occurs first, rather than
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after the more involved block:
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</p>
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<pre>
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if (!expr) {
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x = y; // putting the smaller block first is more readable
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} else {
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...
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...
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}
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</pre>
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<p>
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But if negating a complex condition is too ugly, then at least
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add braces:
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</p>
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<pre>
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if (complex expr not worth negating) {
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...
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...
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} else {
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x = y;
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}
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</pre>
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<h2><a name="preprocessor">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 name="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 <code>int</code> or <code>long</code>, odds are
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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 <code>size_t</code> (use
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<code>ssize_t</code> only if required).</li>
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<li>If it's file-size related, use uintmax_t, or maybe <code>off_t</code>.</li>
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<li>If it's file-offset related (i.e., signed), use <code>off_t</code>.</li>
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<li>If it's just counting small numbers use <code>unsigned int</code>;
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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 <code>bool</code> type
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and use the corresponding <code>true</code> and <code>false</code> macros.
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It's ok 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 <code>int32_t</code>, <code>uint32_t</code>,
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<code>uint64_t</code>, etc.</li>
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<li>While using <code>bool</code> is good for readability, it comes with
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minor caveats:
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<ul>
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<li>Don't use <code>bool</code> 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 <code>bool</code> in libvirt's
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logical wire protocol, since XDR maps that to its lower-level <code>bool_t</code>
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type, which <b>is</b> fixed-size.</li>
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<li>Don't compare a bool variable against the literal, <code>true</code>,
|
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since a value with a logical non-false value need not be <code>1</code>.
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I.e., don't write <code>if (seen == true) ...</code>. Rather,
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write <code>if (seen)...</code>.</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 <code>size_t</code>,
|
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<code>pid_t</code> or <code>off_t</code>, use matching types for any
|
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corresponding variables.
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</p>
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<p>
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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>
|
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and fixing all related variables would be too invasive.
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</p>
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|
|
|
<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 memory.h.
|
|
</p>
|
|
|
|
<ul>
|
|
<li><p>To allocate a single object:</p>
|
|
|
|
<pre>
|
|
virDomainPtr domain;
|
|
|
|
if (VIR_ALLOC(domain) < 0) {
|
|
virReportOOMError();
|
|
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) {
|
|
virReportOOMError();
|
|
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) {
|
|
virReportOOMError();
|
|
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) {
|
|
virReportOOMError();
|
|
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) {
|
|
virReportOOMError();
|
|
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>
|
|
|
|
<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 HAVE_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 or
|
|
libvirt/virterror.h. It is included by "internal.h" already and there
|
|
are some special reasons why you cannot include these files
|
|
explicitly.
|
|
</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>
|