linux-kernel - Re: [PATCH] mtd: allow mtd and jffs2 when ARCH=um

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Message-ID: <1292356893.29257.1.camel@koala>
Date:	Tue, 14 Dec 2010 22:01:33 +0200
From:	Artem Bityutskiy <dedekind1@...il.com>
To:	Jason Lunz <lunz@....org>
Cc:	richard -rw- weinberger <richard.weinberger@...il.com>,
	Sam Ravnborg <sam@...nborg.org>,
	David Woodhouse <dwmw2@...radead.org>,
	atom ota <atomota@...epyhammer.com>,
	user-mode-linux-devel@...ts.sourceforge.net,
	Jeff Dike <jdike@...toit.com>,
	lkml <linux-kernel@...r.kernel.org>,
	linux-mtd@...ts.infradead.org, Rob Landley <rob@...dley.net>
Subject: Re: [PATCH] mtd: allow mtd and jffs2 when ARCH=um

On Tue, 2010-12-14 at 11:51 -0800, Jason Lunz wrote:
> On Tue, Dec 14, 2010 at 06:24:38PM +0200, Artem Bityutskiy wrote:
> > But I think your solution is a bit dirty, because it adds a great deal
> > of little 'if HAS_IOMEM' and '#ifdef CONFIG_HAS_IOMEM' to many places.
> > This is error-prone.
> 
> The intent of that patch was to allow as much of the mtd subsystem to
> compile as possible. My thinking was to try and rectify the fact that
> uml has gone without mtd (and hence jffs2) support for years even though
> much of it works just fine. I think the entire subsystem being marked
> BROKEN in kconfig kept anyone from experimenting with it.
> 
> The patch I sent was actually a reaction to feedback I got from Sam
> Ravnborg on my last attempt (um, three years ago :/ ) in which he
> suggested pushing down the ifdefs closer to their points of use. But I
> agree, the minimal version has a much smaller footprint.
> 
> The version below still meets the goal of allowing jffs2-on-block2mtd
> usage under uml but is much smaller because only the mtd core is
> included. Compile-tested on i386, x86_64, um/i386, and um/x86_64.
> 
> > Instead, you should solve this problem in UML code. I do not know how,
> > but may be you can add readb/writeb there which actually do nothing or
> > print a scary warning, or do BUG(), and let things which use them just
> > fail run-time.
> 
> Something like this could work, but it would be error-prone for anyone
> else who attempts using iomem-requiring drivers on uml. Instead of
> getting obvious compile failures we'd have broken drivers that BUG() or
> emit scary warnings. That doesn't seem to me like an improvement.

This problem does not seem to be mtd-specific, right? So my point was
that it would be nicer to come up with a general solution.

-- 
Best Regards,
Artem Bityutskiy (Битюцкий Артём)

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