On Sat, Mar 20, 2021 at 7:33 PM Lukas Bulwahn [off-list ref] wrote:

Dwaipayan, see my comments below inline.

Fix those minor issues, give the report to somebody else for another
review (and get some more comments), and then I think we are all good
to publish this.

Sure I will fix them. How are we going to publish it? We just share the link it
is hosted on or something else?

Lukas

quoted

---
title: "Linux Kernel checkpatch.pl mentorship"
date: 2021-03-06T02:05:17+05:30
draft: false
---

## Checkpatch - What is it?
[checkpatch.pl](https://github.com/torvalds/linux/blob/master/scripts/checkpatch.pl) is a trivial style checker for patches sent to the linux kernel.

Why is it needed you say?</br>
I did an analysis on checkpatch warnings on about 50k commits from v5.4.</br>
(Find the full report {{% link checkpatch_out_50k.txt %}}here{{% /link %}})

The top errors were then generated via the following shell command:
```/bin/bash
cat checkpatch_out_50k.txt | grep -oP "(?:WARNING|ERROR|CHECK):(\w+)" \
| sort | uniq -c | sort -nr  | head -n6

Count of errors | Error Types | Error
----------------|-------------|------
41999 | <span style="color:green">CHECK</span> | CAMELCASE
13629 | <span style="color:green">CHECK</span> | PARENTHESIS_ALIGNMENT
11491 | <span style="color:orange">WARNING</span> | LONG_LINE
8106 | <span style="color:green">CHECK</span> | SPACING
6825 | <span style="color:orange">WARNING</span> | LEADING_SPACE
4394 | <span style="color:green">CHECK</span> | OPEN_ENDED_LINE

Hmm...The no. of stylistically incorrect bits still continue to exist and

Drop the Hmm... or replace it by "As we can see,"

Replace no. by number. (It is not good to abbreviate here.)

Okay will do.

quoted

are still merged into the kernel code. To make the kernel code more
stylistically coherent, we can:

quoted

- Create cleanup patches for the existing code
- Make sure new patches are stylistically consistent

Both of these are where checkpatch comes handy.

## Checkpatch in the patch submission process

Before sending out the patches to the mailing list, it is recommended to
run checkpatch over the patches.

In general, a Kernel developer would:

quoted

- Create the patch with his proposed changes.
- Build check the patch, run additional tools like checkstack, sparse etc.

maybe add "check for compiler warnings",
checkstack does not exist anymore.

Oops the documentation seems to be outdated then.
https://www.kernel.org/doc/html/latest/process/submit-checklist.html
point no. 10
Will correct

such as sparse and coccinelle

quoted

quoted

- Run checkpatch.pl over the patches to eliminate all trivial style violations.
- Send out the patch to the maintainers and mailing list.

The only catch here is that checkpatch is not always right. It is just a dumb
perl script. If the code looks better with checkpatch errors, let it be.

This is fine to say for the author or as direct advice to a developer, here
I would phrase more neutral.

quoted

## Drawbacks of checkpatch

Checkpatch is only a static trivial style checker. It does not have the
capabilities of a full c based parser like [clang-format](https://www.kernel.org/doc/html/latest/process/clang-format.html). In this sense it is limited in

write instead
"a tool using a full-fledged C parser, such as clang-format"

quoted

what it can do. Still, it is highly valuable as a style checker tool and can
ease the work of maintainers and increase the chances of the patch being accepted
by the community.

## What did we do to improve it?

Over the first 3 months of my mentorship period, I primarily focused on

s/3/three/

(write out numbers up to twelve).

quoted

eliminating false-positives from checkpatch as well as adding new rules.

s/false-positives/false positives/

quoted

Consider the following patch commit log:

#include asm/bitsperlong.h avoid further potential userspace pollution
by moving the #define of SHIFT_PER_LONG to bitops.h which is not
exported to userspace.

A kernel developer in 2020 would not see any checkpatch warning.

A kernel developer in 2021 would see the following warning:
```\bin\bash
WARNING: Commit log lines starting with '#' are dropped by git as comments
#82:
#include asm/bitsperlong.h avoid further potential userspace pollution

During the last 3 months I worked on two major features:

s/3/three/

quoted

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- Addition of a verbose mode to checkpatch
- Addition of an external documentation to checkpatch

For the documentation we decided to document all checkpatch message types,
their meanings and how to resolve them. This is still a work in progress.
Contributions are definitely welcome :-P.

Drop the :-P ; you are serious, we want to see contributions from others.

quoted

### Verbose Mode

This was one of the new additions we did to checkpatch.

One can run checkpatch like this:

```/bin/bash
./scripts/checkpatch.pl -v test.patch

All verbose descriptions can be seen by pairing the verbose option
with --list-types:

```/bin/bash
./scripts/checkpatch.pl --list-types -v

### Checkpatch Documentation

The checkpatch documentation can be viewed from the kernel root
at `Documentation/dev-tools/checkpatch.rst`.

simply:
 The checkpatch documentation is at `Documentation/dev-tools/checkpatch.rst`
 in the kernel repository.

quoted

To build the documentation make sure you have configured sphynx
either in the system or in a python virtualenv. Next the kernel
doc can be built using:

```/bin/bash
make htmldocs

## How to contribute to the documentation?

The documentation is still a work in progress. Feel free to send
the patches to the kernel-doc mailing list, and add me (Dwaipayan
Ray <dwaipayanray1@gmail.com>) and Lukas (Lukas Bulwahn <lukas.bulwahn@gmail.com>) for reviewing it.

The documentation is writted in rst syntax. Refer
[here](http://openalea.gforge.inria.fr/doc/openalea/doc/_build/html/source/sphinx/rest_syntax.html) for a quick guide.

Before sending out the mail, please always:

s/writted/written/
s/mail/patch/

quoted

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- checkpatch.pl your changes
- build check your patch (in this case check the generated html docs)
- spell check your patch (this can be easily done through checkpatch
  using --codespell flag if you already have the codespell dictionary)

## Acknowledgements

During my mentorship period I learned a lot from my mentors.
I would like to thank Lukas for his constant support as my mentor,
Joe for his guidance with checkpatch and everyone in the community for being such
amazing people.

quoted

The kernel contribution process may look old but it works. This is due to the dedication of everyone in the community, which I am glad to be a part of.

I think you need to explain that this is something you learned in this
mentorship, and that newcomers might think at first, but where you
have been surprised.

Yes sure I will be elaborating a bit on these. I feel that I should be able
to motivate others to enter this process.

Thanks for the review Lukas. I will be making the necessary changes.

Thanks & Regards,
Dwaipayan.
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