Documentation/process/4.Coding.rst

6 While there is much to be said for a solid and community-oriented design
19 ---------
25 :ref:`Documentation/process/coding-style.rst <codingstyle>`.  For much of
38 strangely-formatted code.
43 giving up a degree of control in a number of ways - including control over
49 as a way of getting their name into the kernel changelogs - or both.  But
59 80-column limit, for example), just do it.
61 Note that you can also use the ``clang-format`` tool to help you with
62 these rules, to quickly re-format parts of your code automatically,
66 See the file :ref:`Documentation/process/clang-format.rst <clangformat>`
85 implements this extra argument has been broken in some subtle way which was
86 never noticed - because it has never been used.  Or, when the need for
92 Abstraction layers which hide access to hardware - often to allow the bulk
93 of a driver to be used with multiple operating systems - are especially
118 Conditionally-compiled code can be confined to functions which, if the code
139 That, in turn, creates pressure on the processor's memory caches, which can
175 however, this document is being written on a dual-core laptop.  Even on
176 single-processor systems, work being done to improve responsiveness will
216 user-space ABI.  Once an interface has been exported to user space, it must
217 be supported indefinitely.  This fact makes the creation of user-space
221 user-space interfaces is always required.
225 -------------------
227 For now, at least, the writing of error-free code remains an ideal that few
245 kernel with "make KCFLAGS=-W" to get the full set.
247 The kernel provides several configuration options which turn on debugging
250 testing purposes.  In particular, you should turn on:
252  - FRAME_WARN to get warnings for stack frames larger than a given amount.
256  - DEBUG_OBJECTS will add code to track the lifetime of various objects
262  - DEBUG_SLAB can find a variety of memory allocation and use errors; it
265  - DEBUG_SPINLOCK, DEBUG_ATOMIC_SLEEP, and DEBUG_MUTEXES will find a
282 in an automated manner ahead of time.  Code with any sort of non-trivial
289 are, probably, completely untested.  Untested code tends to be broken code;
290 you could be much more confident of your code if all those error-handling
299 Documentation/fault-injection/fault-injection.rst for more information on
304 user-space and kernel-space addresses, mixture of big-endian and
305 small-endian quantities, the passing of integer values where a set of bit
316 :ref:`Documentation/dev-tools/coccinelle.rst <devtools_coccinelle>`
331 -------------
347 Any code which adds a new user-space interface - including new sysfs or
348 /proc files - should include documentation of that interface which enables
349 user-space developers to know what they are working with.  See
353 The file :ref:`Documentation/admin-guide/kernel-parameters.rst
354 <kernelparameters>` describes all of the kernel's boot-time parameters.
362 specially-formatted comments; these comments can be extracted and formatted
363 in a number of ways by the "kernel-doc" script.  If you are working within
365 them, as appropriate, for externally-available functions.  Even in areas
370 :ref:`Documentation/doc-guide/ <doc_guide>`.
376 for verbosely-commented code.  The code should, itself, be readable, with
383 Non-obvious dependencies between separate bits of code should be pointed
389 --------------------
391 The binary interface provided by the kernel to user space cannot be broken
394 the need arises.  If you find yourself having to work around a kernel API,
402 necessary.  This kind of change should also be broken out into a separate
407 which is broken by the change.  For a widely-used function, this duty can
408 lead to literally hundreds or thousands of changes - many of which are
412 wide-ranging API changes.
416 This will help you to be sure that you have found all in-tree uses of that
417 interface.  It will also alert developers of out-of-tree code that there is
418 a change that they need to respond to.  Supporting out-of-tree code is not
420 not have to make life harder for out-of-tree developers than it needs to