linux-kernel - Re: [patch 2/2] Documentation/process: Add tip tree handbook

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Message-ID: <20181108083051.GI20032@gmail.com>
Date:   Thu, 8 Nov 2018 09:30:51 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        John Stultz <john.stultz@...aro.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Andy Lutomirski <luto@...nel.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Will Deacon <will.deacon@....com>,
        Mark Brown <broonie@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [patch 2/2] Documentation/process: Add tip tree handbook


* Thomas Gleixner <tglx@...utronix.de> wrote:

> +Line breaks
> +^^^^^^^^^^^
> +
> +Restricting line length to 80 characters makes deeply indented code hard to
> +read.  Consider breaking out code into helper functions to avoid excessive
> +line breaking.
> +
> +The 80 character rule is not a strict rule, so please use common sense when
> +breaking lines. Especially format strings should never be broken up.

Might make sense to explain that:

  + The reason for that rule is that if for example we have this printk line:
  +
  +		if (uh_oh()) {
  +			pr_info("Something really bad happened, danger"
  +				"danger, blue smoke reported!\n");
  +		}
  +
  + People would see this message in the syslog:
  +
  +   Thu Nov  8 09:22:33: Something really bad happened, dangerdanger, blue smoke reported!
  +
  + And chances are that in sheer panic they'd type the most distinctive 
  + part of that text as a search pattern for the kernel source tree:
  +
  +   $ git grep -i 'dangerdanger'
  +   $
  +
  + ... and they'd get absolutely no match on that string due to the 
  + col80 broken format string, and confusion and frustration would rise, 
  + in addition to growing amounts of blue smoke.
  +
  + We don't want that, so just write out the single line:

  +		if (uh_oh())
  +			pr_info("Something really bad happened, danger danger, blue smoke reported!\n");
  +
  + Also note two other advantages of writing it like this:
  +
  +  - We saved two curly braces.
  +  - We also added a proper space to 'danger danger' which was the original intended message.

?

> +
> +When splitting function declarations or function calls, then please align
> +the first argument in the second line with the first argument in the first
> +line::
> +
> +  static int long_function_name(struct foobar *barfoo, unsigned int id,
> +  				unsigned int offset)
> +  {
> +
> +  	if (!id) {
> +		ret = longer_function_name(barfoo, DEFAULT_BARFOO_ID,
> +					   offset);

BTW., in this particular case I think small violations of col80 rule are 
even more readable, i.e.:

> +		ret = longer_function_name(barfoo, DEFAULT_BARFOO_ID, offset);

And note that in this example we used 78 colums so we didn't even violate 
the col80 rule. ;-)

Thanks,

	Ingo