linux-kernel - Re: [PATCH] arch/x86/xen: remove depends on CONFIG

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Date:	Mon, 25 Feb 2013 06:37:30 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
Cc:	Dongsheng Song <dongsheng.song@...il.com>,
	Kees Cook <keescook@...omium.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"virtualization@...ts.linux-foundation.org" 
	<virtualization@...ts.linux-foundation.org>,
	Mukesh Rathor <mukesh.rathor@...cle.com>
Subject: Re: [PATCH] arch/x86/xen: remove depends on CONFIG_EXPERIMENTAL

On Mon, Feb 25, 2013 at 12:39:27PM +0000, Stefano Stabellini wrote:
> On Sun, 24 Feb 2013, Greg Kroah-Hartman wrote:
> > 
> > You should not have unstable options in the kernel in the first place,
> > sorry.
>  
> With the premise that the removal of CONFIG_EXPERIMENTAL is not an issue
> for me personally or my work, I am going to give you my 2 cents on the
> matter, but feel free to ignore them :)
> 
> While I understand that CONFIG_EXPERIMENTAL has been abused, I feel that
> rejecting everything that is not fully stable and with external
> interfaces set in stones, might hinder the development of new features.

It's been this way for _years_ this isn't something new (the "you have
to get it right really quickly" problem).  See Documentation/ABI/ for
some words about how you can try to do this.

> After all, given how fast the kernel is moving nowadays,

No faster than it has in the past.

> maintaining a project out-of-tree until is completely ready for
> production can be very expensive. Merging the project earlier and
> completing the development upstream can bring better results.

Yes, but don't go changing user-visable apis when you do so.  That's
been a hard rule for a LONG time.

> But in these cases one wouldn't want to "market" the feature as stable
> yet, because it just isn't. If CONFIG_EXPERIMENTAL is going away, is
> there anything in the kernel that can be used to tag a feature as "I
> wouldn't use it in production if I were you"? Maybe just a comment in
> the kconfig description?

I know this is hard, I've had my own problems with it in the past.  You
don't know if you get an api right until you have a lot of users.  See
our previous "discussions" about this topic on lkml if you are curious
as to the eventual outcome of threads like this:

	Yes, it's hard, but that's kernel programming.

Sorry,

greg k-h
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