linux-kernel - Re: [PATCH v4] printk: Add monotonic, boottime, and realtime timestamps

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Message-Id: <20170807203639.GY3730@linux.vnet.ibm.com>
Date:   Mon, 7 Aug 2017 13:36:39 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Prarit Bhargava <prarit@...hat.com>
Cc:     John Stultz <john.stultz@...aro.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Mark Salyzyn <salyzyn@...roid.com>,
        Jonathan Corbet <corbet@....net>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Christoffer Dall <cdall@...aro.org>,
        Deepa Dinamani <deepa.kernel@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        Joel Fernandes <joelaf@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Nicholas Piggin <npiggin@...il.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Olof Johansson <olof@...om.net>,
        Josh Poimboeuf <jpoimboe@...hat.com>, linux-doc@...r.kernel.org
Subject: Re: [PATCH v4] printk: Add monotonic, boottime, and realtime
 timestamps

On Mon, Aug 07, 2017 at 04:06:09PM -0400, Prarit Bhargava wrote:
> 
> 
> On 08/07/2017 02:47 PM, John Stultz wrote:
> > On Mon, Aug 7, 2017 at 11:04 AM, Prarit Bhargava <prarit@...hat.com> wrote:
> >> On 08/07/2017 12:52 PM, John Stultz wrote:
> >>> Still not quite following why you're updating all the defconfigs. I'd
> >>> make sure the Kconfig default settings are right, and leave updating
> >>> the defconfig to arch/device maintainers. It adds a lot of noise to
> >>> the patch.
> >>
> >> Hmm ... I thought it was up to the patch submitter to make sure that
> >> 'make defconfig' still worked?  Are you sure I can leave that broken?
> >>
> >> /me *really* doesn't want to get yelled at by every arch maintainer.
> > 
> > No. Don't break systems, but at the same time, can't you use the
> > default value in Kconfig to set it properly so the old defconfig
> > settings don't really matter?
> > 
> > Apologies if I've not followed the issue properly, but it is odd, as
> > I'm not sure I can think of a patch I've seen before that had so much
> > defconfig noise in it.  Again, I've not looked into it closely, so it
> > may just be my own ignorance, but it makes me suspect there is a
> > better way.
> > 
> 
> peterz?  Want to offer a suggestion?  The issue is that I'm changing a bool
> config option to an int and that impacts all the arch's defconfigs.  John points
> out that this is a lot of churn and we're both wondering if there's a better way
> to do the configs.

The usual approach is to keep the old bool Kconfig option, and add another
int Kconfig option that depends on the original one.  The tests for
the int value get a bit more complex, but one way to handle this is to
define a cpp macro something like the following:

#ifdef CONFIG_OLD_OPTION
#define CPP_NEW_OPTION 0
#else
#define CPP_NEW_OPTION CONFIG_NEW_OPTION
#endif

Then use CPP_NEW_OPTION, where zero means disabled and other numbers
select the available options.

Adjust to suit depending on what values mean what.

Another approach is to make the range of the new Kconfig option
depend on the old option:

config NEW_OPTION
	int "your description here"
	range 1 5 if OLD_OPTION
	range 0 0 if !OLD_OPTION
	default 0
	help
	  your help here

Again, adjust to suit depending on what values mean what.

							Thanx, Paul