linux-kernel - Re: [PATCH] checkpatch/coding-style: Allow 100 column lines

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Message-Id: <F5AE90A2-1661-4B8E-A884-C3CBAB0F603F@dilger.ca>
Date:   Sat, 30 May 2020 16:14:01 -0600
From:   Andreas Dilger <adilger@...ger.ca>
To:     Joe Perches <joe@...ches.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        David Laight <David.Laight@...lab.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        David Howells <dhowells@...hat.com>,
        Christoph Hellwig <hch@....de>,
        Al Viro <viro@...iv.linux.org.uk>, Ian Kent <raven@...maw.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        NetFilter <netfilter-devel@...r.kernel.org>
Subject: Re: [PATCH] checkpatch/coding-style: Allow 100 column lines

On May 29, 2020, at 5:12 PM, Joe Perches <joe@...ches.com> wrote:
> 
> Change the maximum allowed line length to 100 from 80.

What is the benefit/motivation for changing this?  The vast majority
of files are wrapped at 80 columns, and if some files start being
wrapped at 100 columns they will either display poorly on 80-column
terminals, or a lot of dead space will show in 100-column terminals.

> Miscellanea:
> 
> o to avoid unnecessary whitespace changes in files,
>  checkpatch will no longer emit a warning about line length
>  when scanning files unless --strict is also used
> o Add a bit to coding-style about alignment to open parenthesis
> 
> Signed-off-by: Joe Perches <joe@...ches.com>
> ---
> Documentation/process/coding-style.rst | 25 ++++++++++++++++---------
> scripts/checkpatch.pl                  | 14 +++++++++-----
> 2 files changed, 25 insertions(+), 14 deletions(-)
> 
> diff --git a/Documentation/process/coding-style.rst b/Documentation/process/coding-style.rst
> index acb2f1b36350..55b148e9c6b8 100644
> --- a/Documentation/process/coding-style.rst
> +++ b/Documentation/process/coding-style.rst
> @@ -84,15 +84,22 @@ Get a decent editor and don't leave whitespace at the end of lines.
> Coding style is all about readability and maintainability using commonly
> available tools.
> 
> -The limit on the length of lines is 80 columns and this is a strongly
> -preferred limit.
> -
> -Statements longer than 80 columns will be broken into sensible chunks, unless
> -exceeding 80 columns significantly increases readability and does not hide
> -information. Descendants are always substantially shorter than the parent and
> -are placed substantially to the right. The same applies to function headers
> -with a long argument list. However, never break user-visible strings such as
> -printk messages, because that breaks the ability to grep for them.
> +The preferred limit on the length of a single line is 80 columns.
> +
> +Statements longer than 80 columns should be broken into sensible chunks,
> +unless exceeding 80 columns significantly increases readability and does
> +not hide information.
> +
> +Statements may be up to 100 columns when appropriate.
> +
> +Descendants are always substantially shorter than the parent and are
> +are placed substantially to the right.  A very commonly used style
> +is to align descendants to a function open parenthesis.
> +
> +These same rules are applied to function headers with a long argument list.
> +
> +However, never break user-visible strings such as printk messages because
> +that breaks the ability to grep for them.
> 
> 
> 3) Placing Braces and Spaces
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> index dd750241958b..5f00df2c3f59 100755
> --- a/scripts/checkpatch.pl
> +++ b/scripts/checkpatch.pl
> @@ -53,7 +53,7 @@ my %ignore_type = ();
> my @ignore = ();
> my $help = 0;
> my $configuration_file = ".checkpatch.conf";
> -my $max_line_length = 80;
> +my $max_line_length = 100;
> my $ignore_perl_version = 0;
> my $minimum_perl_version = 5.10.0;
> my $min_conf_desc_length = 4;
> @@ -99,9 +99,11 @@ Options:
>   --types TYPE(,TYPE2...)    show only these comma separated message types
>   --ignore TYPE(,TYPE2...)   ignore various comma separated message types
>   --show-types               show the specific message type in the output
> -  --max-line-length=n        set the maximum line length, if exceeded, warn
> +  --max-line-length=n        set the maximum line length, (default $max_line_length)
> +                             if exceeded, warn on patches
> +                             requires --strict for use with --file
>   --min-conf-desc-length=n   set the min description length, if shorter, warn
> -  --tab-size=n               set the number of spaces for tab (default 8)
> +  --tab-size=n               set the number of spaces for tab (default $tabsize)
>   --root=PATH                PATH to the kernel tree root
>   --no-summary               suppress the per-file summary
>   --mailback                 only produce a report in case of warnings/errors
> @@ -3282,8 +3284,10 @@ sub process {
> 
> 			if ($msg_type ne "" &&
> 			    (show_type("LONG_LINE") || show_type($msg_type))) {
> -				WARN($msg_type,
> -				     "line over $max_line_length characters\n" . $herecurr);
> +				my $msg_level = \&WARN;
> +				$msg_level = \&CHK if ($file);
> +				&{$msg_level}($msg_type,
> +					      "line length of $length exceeds $max_line_length columns\n" . $herecurr);
> 			}
> 		}
> 
> 


Cheers, Andreas






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