.. SPDX-License-Identifier: GPL-2.0-only ==========Checkpatch========== Checkpatch (scripts/checkpatch.pl) is a perl script which checks for trivialstyle violations in patches and optionally corrects them.  Checkpatch canalso be run on file contexts and without the kernel tree. Checkpatch is not always right. Your judgement takes precedence over checkpatchmessages.  If your code looks better with the violations, then its probablybest 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 messagesin 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   **CONSTANT_CONVERSION**    Use of __constant_<foo> form is discouraged for the following functions::       __constant_cpu_to_be[x]      __constant_cpu_to_le[x]      __constant_be[x]_to_cpu      __constant_le[x]_to_cpu      __constant_htons      __constant_ntohs     Using any of these outside of include/uapi/ is not preferred as using the    function without __constant_ is identical when the argument is a    constant.     In big endian systems, the macros like __constant_cpu_to_be32(x) and    cpu_to_be32(x) expand to the same expression::       #define __constant_cpu_to_be32(x) ((__force __be32)(__u32)(x))      #define __cpu_to_be32(x)          ((__force __be32)(__u32)(x))     In little endian systems, the macros __constant_cpu_to_be32(x) and    cpu_to_be32(x) expand to __constant_swab32 and __swab32.  __swab32    has a __builtin_constant_p check::       #define __swab32(x)				\        (__builtin_constant_p((__u32)(x)) ?	\        ___constant_swab32(x) :			\        __fswab32(x))     So ultimately they have a special case for constants.    Similar is the case with all of the macros in the list.  Thus    using the __constant_... forms are unnecessarily verbose and    not preferred outside of include/uapi.     See: https://lore.kernel.org/lkml/1400106425.12666.6.camel@joe-AO725/   **DEPRECATED_API**    Usage of a deprecated RCU API is detected.  It is recommended to replace    old flavourful RCU APIs by their new vanilla-RCU counterparts.     The full list of available RCU APIs can be viewed from the kernel docs.     See: https://www.kernel.org/doc/html/latest/RCU/whatisRCU.html#full-list-of-rcu-apis   **DEPRECATED_VARIABLE**    EXTRA_{A,C,CPP,LD}FLAGS are deprecated and should be replaced by the new    flags added via commit f77bf01425b1 ("kbuild: introduce ccflags-y,    asflags-y and ldflags-y").     The following conversion scheme maybe used::       EXTRA_AFLAGS    ->  asflags-y      EXTRA_CFLAGS    ->  ccflags-y      EXTRA_CPPFLAGS  ->  cppflags-y      EXTRA_LDFLAGS   ->  ldflags-y     See:       1. https://lore.kernel.org/lkml/20070930191054.GA15876@uranus.ravnborg.org/      2. https://lore.kernel.org/lkml/1313384834-24433-12-git-send-email-lacombar@gmail.com/      3. https://www.kernel.org/doc/html/latest/kbuild/makefiles.html#compilation-flags   **DEVICE_ATTR_FUNCTIONS**    The function names used in DEVICE_ATTR is unusual.    Typically, the store and show functions are used with <attr>_store and    <attr>_show, where <attr> is a named attribute variable of the device.     Consider the following examples::       static DEVICE_ATTR(type, 0444, type_show, NULL);      static DEVICE_ATTR(power, 0644, power_show, power_store);     The function names should preferably follow the above pattern.     See: https://www.kernel.org/doc/html/latest/driver-api/driver-model/device.html#attributes   **DEVICE_ATTR_RO**    The DEVICE_ATTR_RO(name) helper macro can be used instead of    DEVICE_ATTR(name, 0444, name_show, NULL);     Note that the macro automatically appends _show to the named    attribute variable of the device for the show method.     See: https://www.kernel.org/doc/html/latest/driver-api/driver-model/device.html#attributes   **DEVICE_ATTR_RW**    The DEVICE_ATTR_RW(name) helper macro can be used instead of    DEVICE_ATTR(name, 0644, name_show, name_store);     Note that the macro automatically appends _show and _store to the    named attribute variable of the device for the show and store methods.     See: https://www.kernel.org/doc/html/latest/driver-api/driver-model/device.html#attributes   **DEVICE_ATTR_WO**    The DEVICE_AATR_WO(name) helper macro can be used instead of    DEVICE_ATTR(name, 0200, NULL, name_store);     Note that the macro automatically appends _store to the    named attribute variable of the device for the store method.     See: https://www.kernel.org/doc/html/latest/driver-api/driver-model/device.html#attributes   **DUPLICATED_SYSCTL_CONST**    Commit d91bff3011cf ("proc/sysctl: add shared variables for range    check") added some shared const variables to be used instead of a local    copy in each source file.     Consider replacing the sysctl range checking value with the shared    one in include/linux/sysctl.h.  The following conversion scheme may    be used::       &zero     ->  SYSCTL_ZERO      &one      ->  SYSCTL_ONE      &int_max  ->  SYSCTL_INT_MAX     See:       1. https://lore.kernel.org/lkml/20190430180111.10688-1-mcroce@redhat.com/      2. https://lore.kernel.org/lkml/20190531131422.14970-1-mcroce@redhat.com/   **ENOSYS**    ENOSYS means that a nonexistent system call was called.    Earlier, it was wrongly used for things like invalid operations on    otherwise valid syscalls.  This should be avoided in new code.     See: https://lore.kernel.org/lkml/5eb299021dec23c1a48fa7d9f2c8b794e967766d.1408730669.git.luto@amacapital.net/   **ENOTSUPP**    ENOTSUPP is not a standard error code and should be avoided in new patches.    EOPNOTSUPP should be used instead.     See: https://lore.kernel.org/netdev/20200510182252.GA411829@lunn.ch/   **EXPORT_SYMBOL**    EXPORT_SYMBOL should immediately follow the symbol to be exported.   **IN_ATOMIC**    in_atomic() is not for driver use so any such use is reported as an ERROR.    Also in_atomic() is often used to determine if sleeping is permitted,    but it is not reliable in this use model.  Therefore its use is    strongly discouraged.     However, in_atomic() is ok for core kernel use.     See: https://lore.kernel.org/lkml/20080320201723.b87b3732.akpm@linux-foundation.org/   **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.   **USLEEP_RANGE**    usleep_range() should be preferred over udelay(). The proper way of    using usleep_range() is mentioned in the kernel docs.     See: https://www.kernel.org/doc/html/latest/timers/timers-howto.html#delays-information-on-the-various-kernel-delay-sleep-mechanisms  Comments--------   **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. 

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