linux-kernel - Re: [PATCHv2 2/3] x86, ptdump: Simplify page flag evaluation code

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Message-ID: <CA+rthh9HRMg0E3gE11F+KSdyMpjYC6d=gZhcu5-1TDqMfAw3Uw@mail.gmail.com>
Date:	Thu, 25 Sep 2014 21:27:23 +0200
From:	Mathias Krause <minipli@...glemail.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Arjan van de Ven <arjan@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	x86-ml <x86@...nel.org>
Subject: Re: [PATCHv2 2/3] x86, ptdump: Simplify page flag evaluation code

On 24 September 2014 09:45, Ingo Molnar <mingo@...nel.org> wrote:
> * Mathias Krause <minipli@...glemail.com> wrote:
>> On 21 September 2014 21:49, Arjan van de Ven <arjan@...ux.intel.com> wrote:
>> > On 9/21/2014 8:26 AM, Mathias Krause wrote:
>> >>
>> >> -               if (pr & _PAGE_PCD)
>> >> -                       pt_dump_cont_printf(m, dmsg, "PCD ");
>> >> -               else
>> >> -                       pt_dump_cont_printf(m, dmsg, "    ");
>> >> +               pt_dump_cont(m, dmsg, "%-4s", pr & _PAGE_USER ? "USR" :
>> >> "");
>> >
>> >
>> > while you have some nice cleanups in your patch, I can't say I consider this
>> > an improvement.
>> > Yes the C standard allows ? to be used like this
>> > but no, I don't think it improves readability in general.
>>
>> Not in general, but in this case, it does, IMHO.
>>
>> > (I think for me the main exception is NULL pointer cases, but this is not
>> > one of these)
>>
>> Apparently such a pattern (using the question mark operator combined
>> with a bit test to choose string constants) is used quite often in the
>> linux kernel as a simple grep tells me (probably catches a few false
>> positives but still a representative number):
>
> Both can be used (although I too find the original version easier
> to read), and it's usually the taste/opinion of the original
> author whose choice we prefer.

So I should start writing more code from the scratch than changing
others... ;)

But concerning this patch, are you interested in the following other
pieces:
- changing the macros from being a compound statement expression to
  the common 'do .. while(0)' pattern
- use of pr_info()/pr_cont() instead of printk(KERN_INFO/KERN_CONT)
- use of format strings in pt_dump_cont_printf() calls
- removing the trailing blank before '\n' in the "... # entries
  skipped ..." message
...or should I just drop patch 2 altogether?


Thanks,
Mathias
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