linux-kernel - Re: [ANNOUNCE] GSoC project: Improving kconfig using a SAT solver

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Message-ID: <alpine.DEB.2.01.1005172258360.27232@asgard.lang.hm>
Date:	Mon, 17 May 2010 23:03:10 -0700 (PDT)
From:	david@...g.hm
To:	James Bottomley <James.Bottomley@...senPartnership.com>
cc:	Vegard Nossum <vegard.nossum@...il.com>,
	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	linux-kbuild@...r.kernel.org, Bart Massey <bart@...pdx.edu>,
	Michal Marek <mmarek@...e.cz>,
	Greg Kroah-Hartman <greg@...ah.com>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [ANNOUNCE] GSoC project: Improving kconfig using a SAT solver

On Mon, 17 May 2010, James Bottomley wrote:

> On Mon, 2010-05-17 at 16:21 +0200, Vegard Nossum wrote:
>> On 17 May 2010 15:21, James Bottomley
>>
>> Even if the problem is different from zypper's, it is also here
>> possible to get an unsatisfiable instance. You are right that, yes,
>> the kconfig files on their own should always be satisfiable. But
>> that's before the user has made any choices at all. An example of an
>> unsatisfiable instance would be one where the user demands that 1.
>> some USB driver is enabled, while 2. USB support in general is
>> disabled.
>
> Actually, these are two separate problems.  The first is basic
> consistency within the Kconfig subsytstem (something that select
> currently damages for us).  The second is what to present to the user,
> which is where the inception of the select problem came from.  A user
> doesn't really want to know that USB device X depends on usb storage,
> SCSI and a raft of other things ... they just want it to configure a
> kernel that supports their device.  In particular, we don't want to
> present every possible option to users and then try to work out a
> solution, we really need guided configuration (which, in some measure,
> is what we have today: if you don't select general USB, you won't see
> any USB drivers.  Or more importantly, if you select an Adaptec SCSI
> card, we just enable whichever transport library it needs).

There are two modes people can be in when configuring a kernel.

1. I want to configure a kernel to support my hardware, enable anything 
else needed to make it work.

2. I really care about having a small kernel, don't enable anything I have 
disabled (but help me figure out why something I want isn't available)

I don't think that hiding hardware from the user is ever the best thing to 
do. for approach #1 you obviously don't want to hide anything, but even 
for approach #2, someone may not realize that by disabling one option they 
are making it impossible to support something, and as someone who spent a 
bunch of time hunting through config to find options that I ended up 
finding were not available without enabling something else, I much prefer 
to see the option, but see it disabled rather than not being sure if it 
should be there, or somewhere else in the config.

David Lang
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