linux/Documentation/process/coding-style.rst

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clang-format: add configuration file clang-format is a tool to format C/C++/... code according to a set of rules and heuristics. Like most tools, it is not perfect nor covers every single case, but it is good enough to be helpful. In particular, it is useful for quickly re-formatting blocks of code automatically, for reviewing full files in order to spot coding style mistakes, typos and possible improvements. It is also handy for sorting ``#includes``, for aligning variables and macros, for reflowing text and other similar tasks. It also serves as a teaching tool/guide for newcomers. The tool itself has been already included in the repositories of popular Linux distributions for a long time. The rules in this file are intended for clang-format >= 4, which is easily available in most distributions. This commit adds the configuration file that contains the rules that the tool uses to know how to format the code according to the kernel coding style. This gives us several advantages: * clang-format works out of the box with reasonable defaults; avoiding that everyone has to re-do the configuration. * Everyone agrees (eventually) on what is the most useful default configuration for most of the kernel. * If it becomes commonplace among kernel developers, clang-format may feel compelled to support us better. They already recognize the Linux kernel and its style in their documentation and in one of the style sub-options. Some of clang-format's features relevant for the kernel are: * Uses clang's tooling support behind the scenes to parse and rewrite the code. It is not based on ad-hoc regexps. * Supports reasonably well the Linux kernel coding style. * Fast enough to be used at the press of a key. * There are already integrations (either built-in or third-party) for many common editors used by kernel developers (e.g. vim, emacs, Sublime, Atom...) that allow you to format an entire file or, more usefully, just your selection. * Able to parse unified diffs -- you can, for instance, reformat only the lines changed by a git commit. * Able to reflow text comments as well. * Widely supported and used by hundreds of developers in highly complex projects and organizations (e.g. the LLVM project itself, Chromium, WebKit, Google, Mozilla...). Therefore, it will be supported for a long time. See more information about the tool at: https://clang.llvm.org/docs/ClangFormat.html https://clang.llvm.org/docs/ClangFormatStyleOptions.html Link: http://lkml.kernel.org/r/20180318171632.qfkemw3mwbcukth6@gmail.com Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com> Cc: Randy Dunlap <rdunlap@infradead.org> Cc: Andy Whitcroft <apw@canonical.com> Cc: Joe Perches <joe@perches.com> Cc: Jonathan Corbet <corbet@lwn.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2018-04-10 16:32:40 -07:00
coding-style.rst: document BUG() and WARN() rules ("do not crash the kernel") Linus notes [1] that the introduction of new code that uses VM_BUG_ON() is just as bad as BUG_ON(), because it will crash the kernel on distributions that enable CONFIG_DEBUG_VM (like Fedora): VM_BUG_ON() has the exact same semantics as BUG_ON. It is literally no different, the only difference is "we can make the code smaller because these are less important". [2] This resulted in a more generic discussion about usage of BUG() and friends. While there might be corner cases that still deserve a BUG_ON(), most BUG_ON() cases should simply use WARN_ON_ONCE() and implement a recovery path if reasonable: The only possible case where BUG_ON can validly be used is "I have some fundamental data corruption and cannot possibly return an error". [2] As a very good approximation is the general rule: "absolutely no new BUG_ON() calls _ever_" [2] ... not even if something really shouldn't ever happen and is merely for documenting that an invariant always has to hold. However, there are sill exceptions where BUG_ON() may be used: If you have a "this is major internal corruption, there's no way we can continue", then BUG_ON() is appropriate. [3] There is only one good BUG_ON(): Now, that said, there is one very valid sub-form of BUG_ON(): BUILD_BUG_ON() is absolutely 100% fine. [2] While WARN will also crash the machine with panic_on_warn set, that's exactly to be expected: So we have two very different cases: the "virtual machine with good logging where a dead machine is fine" - use 'panic_on_warn'. And the actual real hardware with real drivers, running real loads by users. [4] The basic idea is that warnings will similarly get reported by users and be found during testing. However, in contrast to a BUG(), there is a way to actually influence the expected behavior (e.g., panic_on_warn) and to eventually keep the machine alive to extract some debug info. Ingo notes that not all WARN_ON_ONCE cases need recovery. If we don't ever expect this code to trigger in any case, recovery code is not really helpful. I'd prefer to keep all these warnings 'simple' - i.e. no attempted recovery & control flow, unless we ever expect these to trigger. [5] There have been different rules floating around that were never properly documented. Let's try to clarify. [1] https://lkml.kernel.org/r/CAHk-=wiEAH+ojSpAgx_Ep=NKPWHU8AdO3V56BXcCsU97oYJ1EA@mail.gmail.com [2] https://lore.kernel.org/r/CAHk-=wg40EAZofO16Eviaj7mfqDhZ2gVEbvfsMf6gYzspRjYvw@mail.gmail.com [3] https://lkml.kernel.org/r/CAHk-=wit-DmhMfQErY29JSPjFgebx_Ld+pnerc4J2Ag990WwAA@mail.gmail.com [4] https://lore.kernel.org/r/CAHk-=wgF7K2gSSpy=m_=K3Nov4zaceUX9puQf1TjkTJLA2XC_g@mail.gmail.com [5] https://lore.kernel.org/r/YwIW+mVeZoTOxn%2F4@gmail.com Reviewed-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: David Hildenbrand <david@redhat.com> Link: https://lore.kernel.org/r/20220923113426.52871-2-david@redhat.com Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2022-09-23 13:34:24 +02:00