linux-kernel - Re: [PATCH] Fix line too long warning

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Date:   Sun, 29 Oct 2017 21:34:57 +0300
From:   Yury Norov <ynorov@...iumnetworks.com>
To:     Joe Perches <joe@...ches.com>
Cc:     Kien Ha <kienha9922@...il.com>, linux-kernel@...r.kernel.org,
        devel@...verdev.osuosl.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] Fix line too long warning

On Sun, Oct 29, 2017 at 10:28:27AM -0700, Joe Perches wrote:
> On Sun, 2017-10-29 at 18:54 +0300, Yury Norov wrote:
> > At second, and most important, refer Documentation/process/coding-style.rst:
> > Now, some people will claim that having 8-character indentations makes
> > the code move too far to the right, and makes it hard to read on a 
> > 80-character terminal screen.  The answer to that is that if you need 
> > more than 3 levels of indentation, you're screwed anyway, and should fix
> > your program.
> > 
> > The real problem here is not "line too long", but "indentation level too
> > big" - 5. And it worth to address real problem.
> 
> Line length issues can be a combination of several factors:
> 
> o identifier length
> o quantity of dereferences
> o indentation depth
> o code complexity
> 
> 4 indentation depth levels are not a real issue.
> A significant percentage of lines in the kernel
> are 4 or more tab indent levels deep.
> 
> checkpatch suggests that 6 or more is the depth level
> that should cause real concern.
> 
> Here's a little breakdown of lines that start with
> a tab followed by a c90 keyword in the kernel
> 
> $ git grep -P "^\t+(if|for|do|while|\}|else|switch|return|case|break|continue|goto)\b" -- "*.[ch]" | \
>   cut -f2- -d":" | perl -p -e 's/(^\t+).*/\1/' | \
>   sort | uniq -c | sort -rn | \
>   awk '{total += $1; count[i++] = $1} END { for (j = 0; j < i; j++) { printf "%d\t%d\t%.2f%%\n", j + 1, count[j], count[j] / total * 100 }}'
> 1	1325462	52.19%
> 2	863007	33.98%
> 3	271844	10.70%
> 4	64009	2.52%
> 5	12502	0.49%
> 6	2199	0.09%
> 7	501	0.02%
> 8	166	0.01%
> 9	51	0.00%
> 10	20	0.00%
> 11	10	0.00%
> 12	4	0.00%
> 13	1	0.00%
> 
> I think it could reasonably be argued that the
> indentation depth warning (DEEP_INDENTATION)
> should start at 5 and not at 6.
> 
> ---
>  scripts/checkpatch.pl | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> index 6bdd43d5dec5..923e4ff09d24 100755
> --- a/scripts/checkpatch.pl
> +++ b/scripts/checkpatch.pl
> @@ -3353,7 +3353,7 @@ sub process {
>  
>  			my ($level, @ctx) = ctx_statement_level($linenr, $realcnt, 0);
>  
> -			if ($line =~ /^\+\t{6,}/) {
> +			if ($line =~ /^\+\t{5,}/) {
>  				WARN("DEEP_INDENTATION",
>  				     "Too many leading tabs - consider code refactoring\n" . $herecurr);
>  			}

There are 2 different subjects here - this specific function in staging
driver and general considerations.

Regarding the function, it has very simple structure, and so deep indentation
level is definitely a symptom of bad design.

Regarding general considerations, the kernel is very complex, and I admit
that indentations deeper than 3 are unavoidable in some cases.

But we have coding style that insists on 3, and this rule is (probably ?)
written by Linus, so... :-)

Nevertheless, your patch is the step toward right direction, so if you
need my ack,
Acked-by: Yury Norov <ynorov@...iumnetworks.com>