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Merge tag 'docs-5.13' of git://git.lwn.net/linux

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Pull documentation updates from Jonathan Corbet:
 "It's been a relatively busy cycle in docsland, though more than
  usually well contained to Documentation/ itself. Highlights include:

   - The Chinese translators have been busy and show no signs of
     stopping anytime soon. Italian has also caught up.

   - Aditya Srivastava has been working on improvements to the
     kernel-doc script.

   - Thorsten continues his work on reporting-issues.rst and related
     documentation around regression reporting.

   - Lots of documentation updates, typo fixes, etc. as usual"

* tag 'docs-5.13' of git://git.lwn.net/linux: (139 commits)
  docs/zh_CN: add openrisc translation to zh_CN index
  docs/zh_CN: add openrisc index.rst translation
  docs/zh_CN: add openrisc todo.rst translation
  docs/zh_CN: add openrisc openrisc_port.rst translation
  docs/zh_CN: add core api translation to zh_CN index
  docs/zh_CN: add core-api index.rst translation
  docs/zh_CN: add core-api irq index.rst translation
  docs/zh_CN: add core-api irq irqflags-tracing.rst translation
  docs/zh_CN: add core-api irq irq-domain.rst translation
  docs/zh_CN: add core-api irq irq-affinity.rst translation
  docs/zh_CN: add core-api irq concepts.rst translation
  docs: sphinx-pre-install: don't barf on beta Sphinx releases
  scripts: kernel-doc: improve parsing for kernel-doc comments syntax
  docs/zh_CN: two minor fixes in zh_CN/doc-guide/
  Documentation: dev-tools: Add Testing Overview
  docs/zh_CN: add translations in zh_CN/dev-tools/gcov
  docs: reporting-issues: make people CC the regressions list
  MAINTAINERS: add regressions mailing list
  doc:it_IT: align Italian documentation
  docs/zh_CN: sync reporting-issues.rst
  ...
This commit is contained in:
Linus Torvalds
2021-04-26 13:22:43 -07:00
parent 0c85556318 441ca977a8
commit 2f9ef0559e
133 changed files with 9858 additions and 2049 deletions
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Documentation/dev-tools/checkpatch.rst
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.. SPDX-License-Identifier: GPL-2.0-only
==========
Checkpatch
==========
Checkpatch (scripts/checkpatch.pl) is a perl script which checks for trivial
style violations in patches and optionally corrects them. Checkpatch can
also be run on file contexts and without the kernel tree.
Checkpatch is not always right. Your judgement takes precedence over checkpatch
messages. If your code looks better with the violations, then its probably
best left alone.
Options
=======
This section will describe the options checkpatch can be run with.
Usage::
./scripts/checkpatch.pl [OPTION]... [FILE]...
Available options:
- -q, --quiet
Enable quiet mode.
- -v, --verbose
Enable verbose mode. Additional verbose test descriptions are output
so as to provide information on why that particular message is shown.
- --no-tree
Run checkpatch without the kernel tree.
- --no-signoff
Disable the 'Signed-off-by' line check. The sign-off is a simple line at
the end of the explanation for the patch, which certifies that you wrote it
or otherwise have the right to pass it on as an open-source patch.
Example::
Signed-off-by: Random J Developer <random@developer.example.org>
Setting this flag effectively stops a message for a missing signed-off-by
line in a patch context.
- --patch
Treat FILE as a patch. This is the default option and need not be
explicitly specified.
- --emacs
Set output to emacs compile window format. This allows emacs users to jump
from the error in the compile window directly to the offending line in the
patch.
- --terse
Output only one line per report.
- --showfile
Show the diffed file position instead of the input file position.
- -g, --git
Treat FILE as a single commit or a git revision range.
Single commit with:
- <rev>
- <rev>^
- <rev>~n
Multiple commits with:
- <rev1>..<rev2>
- <rev1>...<rev2>
- <rev>-<count>
- -f, --file
Treat FILE as a regular source file. This option must be used when running
checkpatch on source files in the kernel.
- --subjective, --strict
Enable stricter tests in checkpatch. By default the tests emitted as CHECK
do not activate by default. Use this flag to activate the CHECK tests.
- --list-types
Every message emitted by checkpatch has an associated TYPE. Add this flag
to display all the types in checkpatch.
Note that when this flag is active, checkpatch does not read the input FILE,
and no message is emitted. Only a list of types in checkpatch is output.
- --types TYPE(,TYPE2...)
Only display messages with the given types.
Example::
./scripts/checkpatch.pl mypatch.patch --types EMAIL_SUBJECT,BRACES
- --ignore TYPE(,TYPE2...)
Checkpatch will not emit messages for the specified types.
Example::
./scripts/checkpatch.pl mypatch.patch --ignore EMAIL_SUBJECT,BRACES
- --show-types
By default checkpatch doesn't display the type associated with the messages.
Set this flag to show the message type in the output.
- --max-line-length=n
Set the max line length (default 100). If a line exceeds the specified
length, a LONG_LINE message is emitted.
The message level is different for patch and file contexts. For patches,
a WARNING is emitted. While a milder CHECK is emitted for files. So for
file contexts, the --strict flag must also be enabled.
- --min-conf-desc-length=n
Set the Kconfig entry minimum description length, if shorter, warn.
- --tab-size=n
Set the number of spaces for tab (default 8).
- --root=PATH
PATH to the kernel tree root.
This option must be specified when invoking checkpatch from outside
the kernel root.
- --no-summary
Suppress the per file summary.
- --mailback
Only produce a report in case of Warnings or Errors. Milder Checks are
excluded from this.
- --summary-file
Include the filename in summary.
- --debug KEY=[0|1]
Turn on/off debugging of KEY, where KEY is one of 'values', 'possible',
'type', and 'attr' (default is all off).
- --fix
This is an EXPERIMENTAL feature. If correctable errors exists, a file
<inputfile>.EXPERIMENTAL-checkpatch-fixes is created which has the
automatically fixable errors corrected.
- --fix-inplace
EXPERIMENTAL - Similar to --fix but input file is overwritten with fixes.
DO NOT USE this flag unless you are absolutely sure and you have a backup
in place.
- --ignore-perl-version
Override checking of perl version. Runtime errors maybe encountered after
enabling this flag if the perl version does not meet the minimum specified.
- --codespell
Use the codespell dictionary for checking spelling errors.
- --codespellfile
Use the specified codespell file.
Default is '/usr/share/codespell/dictionary.txt'.
- --typedefsfile
Read additional types from this file.
- --color[=WHEN]
Use colors 'always', 'never', or only when output is a terminal ('auto').
Default is 'auto'.
- --kconfig-prefix=WORD
Use WORD as a prefix for Kconfig symbols (default is `CONFIG_`).
- -h, --help, --version
Display the help text.
Message Levels
==============
Messages in checkpatch are divided into three levels. The levels of messages
in checkpatch denote the severity of the error. They are:
- ERROR
This is the most strict level. Messages of type ERROR must be taken
seriously as they denote things that are very likely to be wrong.
- WARNING
This is the next stricter level. Messages of type WARNING requires a
more careful review. But it is milder than an ERROR.
- CHECK
This is the mildest level. These are things which may require some thought.
Type Descriptions
=================
This section contains a description of all the message types in checkpatch.
.. Types in this section are also parsed by checkpatch.
.. The types are grouped into subsections based on use.
Allocation style
----------------
**ALLOC_ARRAY_ARGS**
The first argument for kcalloc or kmalloc_array should be the
number of elements. sizeof() as the first argument is generally
wrong.
See: https://www.kernel.org/doc/html/latest/core-api/memory-allocation.html
**ALLOC_SIZEOF_STRUCT**
The allocation style is bad. In general for family of
allocation functions using sizeof() to get memory size,
constructs like::
p = alloc(sizeof(struct foo), ...)
should be::
p = alloc(sizeof(*p), ...)
See: https://www.kernel.org/doc/html/latest/process/coding-style.html#allocating-memory
**ALLOC_WITH_MULTIPLY**
Prefer kmalloc_array/kcalloc over kmalloc/kzalloc with a
sizeof multiply.
See: https://www.kernel.org/doc/html/latest/core-api/memory-allocation.html
API usage
---------
**ARCH_DEFINES**
Architecture specific defines should be avoided wherever
possible.
**ARCH_INCLUDE_LINUX**
Whenever asm/file.h is included and linux/file.h exists, a
conversion can be made when linux/file.h includes asm/file.h.
However this is not always the case (See signal.h).
This message type is emitted only for includes from arch/.
**AVOID_BUG**
BUG() or BUG_ON() should be avoided totally.
Use WARN() and WARN_ON() instead, and handle the "impossible"
error condition as gracefully as possible.
See: https://www.kernel.org/doc/html/latest/process/deprecated.html#bug-and-bug-on
**CONSIDER_KSTRTO**
The simple_strtol(), simple_strtoll(), simple_strtoul(), and
simple_strtoull() functions explicitly ignore overflows, which
may lead to unexpected results in callers. The respective kstrtol(),
kstrtoll(), kstrtoul(), and kstrtoull() functions tend to be the
correct replacements.
See: https://www.kernel.org/doc/html/latest/process/deprecated.html#simple-strtol-simple-strtoll-simple-strtoul-simple-strtoull
**LOCKDEP**
The lockdep_no_validate class was added as a temporary measure to
prevent warnings on conversion of device->sem to device->mutex.
It should not be used for any other purpose.
See: https://lore.kernel.org/lkml/1268959062.9440.467.camel@laptop/
**MALFORMED_INCLUDE**
The #include statement has a malformed path. This has happened
because the author has included a double slash "//" in the pathname
accidentally.
**USE_LOCKDEP**
lockdep_assert_held() annotations should be preferred over
assertions based on spin_is_locked()
See: https://www.kernel.org/doc/html/latest/locking/lockdep-design.html#annotations
**UAPI_INCLUDE**
No #include statements in include/uapi should use a uapi/ path.
Comment style
-------------
**BLOCK_COMMENT_STYLE**
The comment style is incorrect. The preferred style for multi-
line comments is::
/*
* This is the preferred style
* for multi line comments.
*/
The networking comment style is a bit different, with the first line
not empty like the former::
/* This is the preferred comment style
* for files in net/ and drivers/net/
*/
See: https://www.kernel.org/doc/html/latest/process/coding-style.html#commenting
**C99_COMMENTS**
C99 style single line comments (//) should not be used.
Prefer the block comment style instead.
See: https://www.kernel.org/doc/html/latest/process/coding-style.html#commenting
Commit message
--------------
**BAD_SIGN_OFF**
The signed-off-by line does not fall in line with the standards
specified by the community.
See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#developer-s-certificate-of-origin-1-1
**BAD_STABLE_ADDRESS_STYLE**
The email format for stable is incorrect.
Some valid options for stable address are::
1. stable@vger.kernel.org
2. stable@kernel.org
For adding version info, the following comment style should be used::
stable@vger.kernel.org # version info
**COMMIT_COMMENT_SYMBOL**
Commit log lines starting with a '#' are ignored by git as
comments. To solve this problem addition of a single space
infront of the log line is enough.
**COMMIT_MESSAGE**
The patch is missing a commit description. A brief
description of the changes made by the patch should be added.
See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#describe-your-changes
**MISSING_SIGN_OFF**
The patch is missing a Signed-off-by line. A signed-off-by
line should be added according to Developer's certificate of
Origin.
See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#sign-your-work-the-developer-s-certificate-of-origin
**NO_AUTHOR_SIGN_OFF**
The author of the patch has not signed off the patch. It is
required that a simple sign off line should be present at the
end of explanation of the patch to denote that the author has
written it or otherwise has the rights to pass it on as an open
source patch.
See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#sign-your-work-the-developer-s-certificate-of-origin
**DIFF_IN_COMMIT_MSG**
Avoid having diff content in commit message.
This causes problems when one tries to apply a file containing both
the changelog and the diff because patch(1) tries to apply the diff
which it found in the changelog.
See: https://lore.kernel.org/lkml/20150611134006.9df79a893e3636019ad2759e@linux-foundation.org/
**GERRIT_CHANGE_ID**
To be picked up by gerrit, the footer of the commit message might
have a Change-Id like::
Change-Id: Ic8aaa0728a43936cd4c6e1ed590e01ba8f0fbf5b
Signed-off-by: A. U. Thor <author@example.com>
The Change-Id line must be removed before submitting.
**GIT_COMMIT_ID**
The proper way to reference a commit id is:
commit <12+ chars of sha1> ("<title line>")
An example may be::
Commit e21d2170f36602ae2708 ("video: remove unnecessary
platform_set_drvdata()") removed the unnecessary
platform_set_drvdata(), but left the variable "dev" unused,
delete it.
See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#describe-your-changes
Comparison style
----------------
**ASSIGN_IN_IF**
Do not use assignments in if condition.
Example::
if ((foo = bar(...)) < BAZ) {
should be written as::
foo = bar(...);
if (foo < BAZ) {
**BOOL_COMPARISON**
Comparisons of A to true and false are better written
as A and !A.
See: https://lore.kernel.org/lkml/1365563834.27174.12.camel@joe-AO722/
**COMPARISON_TO_NULL**
Comparisons to NULL in the form (foo == NULL) or (foo != NULL)
are better written as (!foo) and (foo).
**CONSTANT_COMPARISON**
Comparisons with a constant or upper case identifier on the left
side of the test should be avoided.
Macros, Attributes and Symbols
------------------------------
**ARRAY_SIZE**
The ARRAY_SIZE(foo) macro should be preferred over
sizeof(foo)/sizeof(foo[0]) for finding number of elements in an
array.
The macro is defined in include/linux/kernel.h::
#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
**AVOID_EXTERNS**
Function prototypes don't need to be declared extern in .h
files. It's assumed by the compiler and is unnecessary.
**AVOID_L_PREFIX**
Local symbol names that are prefixed with `.L` should be avoided,
as this has special meaning for the assembler; a symbol entry will
not be emitted into the symbol table. This can prevent `objtool`
from generating correct unwind info.
Symbols with STB_LOCAL binding may still be used, and `.L` prefixed
local symbol names are still generally usable within a function,
but `.L` prefixed local symbol names should not be used to denote
the beginning or end of code regions via
`SYM_CODE_START_LOCAL`/`SYM_CODE_END`
**BIT_MACRO**
Defines like: 1 << <digit> could be BIT(digit).
The BIT() macro is defined in include/linux/bitops.h::
#define BIT(nr) (1UL << (nr))
**CONST_READ_MOSTLY**
When a variable is tagged with the __read_mostly annotation, it is a
signal to the compiler that accesses to the variable will be mostly
reads and rarely(but NOT never) a write.
const __read_mostly does not make any sense as const data is already
read-only. The __read_mostly annotation thus should be removed.
**DATE_TIME**
It is generally desirable that building the same source code with
the same set of tools is reproducible, i.e. the output is always
exactly the same.
The kernel does *not* use the ``__DATE__`` and ``__TIME__`` macros,
and enables warnings if they are used as they can lead to
non-deterministic builds.
See: https://www.kernel.org/doc/html/latest/kbuild/reproducible-builds.html#timestamps
**DEFINE_ARCH_HAS**
The ARCH_HAS_xyz and ARCH_HAVE_xyz patterns are wrong.
For big conceptual features use Kconfig symbols instead. And for
smaller things where we have compatibility fallback functions but
want architectures able to override them with optimized ones, we
should either use weak functions (appropriate for some cases), or
the symbol that protects them should be the same symbol we use.
See: https://lore.kernel.org/lkml/CA+55aFycQ9XJvEOsiM3txHL5bjUc8CeKWJNR_H+MiicaddB42Q@mail.gmail.com/
**INIT_ATTRIBUTE**
Const init definitions should use __initconst instead of
__initdata.
Similarly init definitions without const require a separate
use of const.
**INLINE_LOCATION**
The inline keyword should sit between storage class and type.
For example, the following segment::
inline static int example_function(void)
{
...
}
should be::
static inline int example_function(void)
{
...
}
**MULTISTATEMENT_MACRO_USE_DO_WHILE**
Macros with multiple statements should be enclosed in a
do - while block. Same should also be the case for macros
starting with `if` to avoid logic defects::
#define macrofun(a, b, c) \
do { \
if (a == 5) \
do_this(b, c); \
} while (0)
See: https://www.kernel.org/doc/html/latest/process/coding-style.html#macros-enums-and-rtl
**WEAK_DECLARATION**
Using weak declarations like __attribute__((weak)) or __weak
can have unintended link defects. Avoid using them.
Functions and Variables
-----------------------
**CAMELCASE**
Avoid CamelCase Identifiers.
See: https://www.kernel.org/doc/html/latest/process/coding-style.html#naming
**FUNCTION_WITHOUT_ARGS**
Function declarations without arguments like::
int foo()
should be::
int foo(void)
**GLOBAL_INITIALISERS**
Global variables should not be initialized explicitly to
0 (or NULL, false, etc.). Your compiler (or rather your
loader, which is responsible for zeroing out the relevant
sections) automatically does it for you.
**INITIALISED_STATIC**
Static variables should not be initialized explicitly to zero.
Your compiler (or rather your loader) automatically does
it for you.
**RETURN_PARENTHESES**
return is not a function and as such doesn't need parentheses::
return (bar);
can simply be::
return bar;
Spacing and Brackets
--------------------
**ASSIGNMENT_CONTINUATIONS**
Assignment operators should not be written at the start of a
line but should follow the operand at the previous line.
**BRACES**
The placement of braces is stylistically incorrect.
The preferred way is to put the opening brace last on the line,
and put the closing brace first::
if (x is true) {
we do y
}
This applies for all non-functional blocks.
However, there is one special case, namely functions: they have the
opening brace at the beginning of the next line, thus::
int function(int x)
{
body of function
}
See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces
**BRACKET_SPACE**
Whitespace before opening bracket '[' is prohibited.
There are some exceptions:
1. With a type on the left::
;int [] a;
2. At the beginning of a line for slice initialisers::
[0...10] = 5,
3. Inside a curly brace::
= { [0...10] = 5 }
**CODE_INDENT**
Code indent should use tabs instead of spaces.
Outside of comments, documentation and Kconfig,
spaces are never used for indentation.
See: https://www.kernel.org/doc/html/latest/process/coding-style.html#indentation
**CONCATENATED_STRING**
Concatenated elements should have a space in between.
Example::
printk(KERN_INFO"bar");
should be::
printk(KERN_INFO "bar");
**ELSE_AFTER_BRACE**
`else {` should follow the closing block `}` on the same line.
See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces
**LINE_SPACING**
Vertical space is wasted given the limited number of lines an
editor window can display when multiple blank lines are used.
See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces
**OPEN_BRACE**
The opening brace should be following the function definitions on the
next line. For any non-functional block it should be on the same line
as the last construct.
See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces
**POINTER_LOCATION**
When using pointer data or a function that returns a pointer type,
the preferred use of * is adjacent to the data name or function name
and not adjacent to the type name.
Examples::
char *linux_banner;
unsigned long long memparse(char *ptr, char **retptr);
char *match_strdup(substring_t *s);
See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces
**SPACING**
Whitespace style used in the kernel sources is described in kernel docs.
See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces
**SWITCH_CASE_INDENT_LEVEL**
switch should be at the same indent as case.
Example::
switch (suffix) {
case 'G':
case 'g':
mem <<= 30;
break;
case 'M':
case 'm':
mem <<= 20;
break;
case 'K':
case 'k':
mem <<= 10;
/* fall through */
default:
break;
}
See: https://www.kernel.org/doc/html/latest/process/coding-style.html#indentation
**TRAILING_WHITESPACE**
Trailing whitespace should always be removed.
Some editors highlight the trailing whitespace and cause visual
distractions when editing files.
See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces
**WHILE_AFTER_BRACE**
while should follow the closing bracket on the same line::
do {
...
} while(something);
See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces
Others
------
**CONFIG_DESCRIPTION**
Kconfig symbols should have a help text which fully describes
it.
**CORRUPTED_PATCH**
The patch seems to be corrupted or lines are wrapped.
Please regenerate the patch file before sending it to the maintainer.
**DOS_LINE_ENDINGS**
For DOS-formatted patches, there are extra ^M symbols at the end of
the line. These should be removed.
**EXECUTE_PERMISSIONS**
There is no reason for source files to be executable. The executable
bit can be removed safely.
**NON_OCTAL_PERMISSIONS**
Permission bits should use 4 digit octal permissions (like 0700 or 0444).
Avoid using any other base like decimal.
**NOT_UNIFIED_DIFF**
The patch file does not appear to be in unified-diff format. Please
regenerate the patch file before sending it to the maintainer.
**PRINTF_0XDECIMAL**
Prefixing 0x with decimal output is defective and should be corrected.
**TRAILING_STATEMENTS**
Trailing statements (for example after any conditional) should be
on the next line.
Like::
if (x == y) break;
should be::
if (x == y)
break;
Documentation/dev-tools/gcov.rst
+6 -2
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@@ -124,6 +124,8 @@ box for setups where kernels are built and run on the same machine. In
cases where the kernel runs on a separate machine, special preparations
must be made, depending on where the gcov tool is used:
.. _gcov-test:
a) gcov is run on the TEST machine
The gcov tool version on the test machine must be compatible with the
@@ -143,6 +145,8 @@ a) gcov is run on the TEST machine
machine. If any of the path components is symbolic link, the actual
directory needs to be used instead (due to make's CURDIR handling).
.. _gcov-build:
b) gcov is run on the BUILD machine
The following files need to be copied after each test case from test
@@ -211,7 +215,7 @@ Appendix A: gather_on_build.sh
------------------------------
Sample script to gather coverage meta files on the build machine
(see 6a):
(see :ref:`Separated build and test machines a. <gcov-test>`):
.. code-block:: sh
@@ -244,7 +248,7 @@ Appendix B: gather_on_test.sh
-----------------------------
Sample script to gather coverage data files on the test machine
(see 6b):
(see :ref:`Separated build and test machines b. <gcov-build>`):
.. code-block:: sh
Documentation/dev-tools/index.rst
+5
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@@ -7,6 +7,9 @@ be used to work on the kernel. For now, the documents have been pulled
together without any significant effort to integrate them into a coherent
whole; patches welcome!
A brief overview of testing-specific tools can be found in
Documentation/dev-tools/testing-overview.rst
.. class:: toc-title
Table of contents
@@ -14,6 +17,8 @@ whole; patches welcome!
.. toctree::
:maxdepth: 2
testing-overview
checkpatch
coccinelle
sparse
kcov
Documentation/dev-tools/testing-overview.rst
+117
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@@ -0,0 +1,117 @@
.. SPDX-License-Identifier: GPL-2.0
====================
Kernel Testing Guide
====================
There are a number of different tools for testing the Linux kernel, so knowing
when to use each of them can be a challenge. This document provides a rough
overview of their differences, and how they fit together.
Writing and Running Tests
=========================
The bulk of kernel tests are written using either the kselftest or KUnit
frameworks. These both provide infrastructure to help make running tests and
groups of tests easier, as well as providing helpers to aid in writing new
tests.
If you're looking to verify the behaviour of the Kernel — particularly specific
parts of the kernel — then you'll want to use KUnit or kselftest.
The Difference Between KUnit and kselftest
------------------------------------------
KUnit (Documentation/dev-tools/kunit/index.rst) is an entirely in-kernel system
for "white box" testing: because test code is part of the kernel, it can access
internal structures and functions which aren't exposed to userspace.
KUnit tests therefore are best written against small, self-contained parts
of the kernel, which can be tested in isolation. This aligns well with the
concept of 'unit' testing.
For example, a KUnit test might test an individual kernel function (or even a
single codepath through a function, such as an error handling case), rather
than a feature as a whole.
This also makes KUnit tests very fast to build and run, allowing them to be
run frequently as part of the development process.
There is a KUnit test style guide which may give further pointers in
Documentation/dev-tools/kunit/style.rst
kselftest (Documentation/dev-tools/kselftest.rst), on the other hand, is
largely implemented in userspace, and tests are normal userspace scripts or
programs.
This makes it easier to write more complicated tests, or tests which need to
manipulate the overall system state more (e.g., spawning processes, etc.).
However, it's not possible to call kernel functions directly from kselftest.
This means that only kernel functionality which is exposed to userspace somehow
(e.g. by a syscall, device, filesystem, etc.) can be tested with kselftest. To
work around this, some tests include a companion kernel module which exposes
more information or functionality. If a test runs mostly or entirely within the
kernel, however, KUnit may be the more appropriate tool.
kselftest is therefore suited well to tests of whole features, as these will
expose an interface to userspace, which can be tested, but not implementation
details. This aligns well with 'system' or 'end-to-end' testing.
For example, all new system calls should be accompanied by kselftest tests.
Code Coverage Tools
===================
The Linux Kernel supports two different code coverage measurement tools. These
can be used to verify that a test is executing particular functions or lines
of code. This is useful for determining how much of the kernel is being tested,
and for finding corner-cases which are not covered by the appropriate test.
:doc:`gcov` is GCC's coverage testing tool, which can be used with the kernel
to get global or per-module coverage. Unlike KCOV, it does not record per-task
coverage. Coverage data can be read from debugfs, and interpreted using the
usual gcov tooling.
:doc:`kcov` is a feature which can be built in to the kernel to allow
capturing coverage on a per-task level. It's therefore useful for fuzzing and
other situations where information about code executed during, for example, a
single syscall is useful.
Dynamic Analysis Tools
======================
The kernel also supports a number of dynamic analysis tools, which attempt to
detect classes of issues when they occur in a running kernel. These typically
each look for a different class of bugs, such as invalid memory accesses,
concurrency issues such as data races, or other undefined behaviour like
integer overflows.
Some of these tools are listed below:
* kmemleak detects possible memory leaks. See
Documentation/dev-tools/kmemleak.rst
* KASAN detects invalid memory accesses such as out-of-bounds and
use-after-free errors. See Documentation/dev-tools/kasan.rst
* UBSAN detects behaviour that is undefined by the C standard, like integer
overflows. See Documentation/dev-tools/ubsan.rst
* KCSAN detects data races. See Documentation/dev-tools/kcsan.rst
* KFENCE is a low-overhead detector of memory issues, which is much faster than
KASAN and can be used in production. See Documentation/dev-tools/kfence.rst
* lockdep is a locking correctness validator. See
Documentation/locking/lockdep-design.rst
* There are several other pieces of debug instrumentation in the kernel, many
of which can be found in lib/Kconfig.debug
These tools tend to test the kernel as a whole, and do not "pass" like
kselftest or KUnit tests. They can be combined with KUnit or kselftest by
running tests on a kernel with these tools enabled: you can then be sure
that none of these errors are occurring during the test.
Some of these tools integrate with KUnit or kselftest and will
automatically fail tests if an issue is detected.