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

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Message-Id: <201012141840.27529.rob@landley.net>
Date:	Tue, 14 Dec 2010 18:40:25 -0600
From:	Rob Landley <rob@...dley.net>
To:	Jason Lunz <lunz@....org>
Cc:	Artem Bityutskiy <dedekind1@...il.com>,
	"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
Subject: Re: [PATCH] mtd: allow mtd and jffs2 when ARCH=um

On Tuesday 14 December 2010 15:23:49 Jason Lunz wrote:
> On one hand you've got uml, which simply doesn't have mmio. On the other
> there's mtd, which began as a method for accessing hardware devices that
> are often accessed using mmio. But then the mtd subsystem developed
> emulations of that hardware that are software based and thus don't
> require mmio. It's mainly these emulated backends I'm interested in
> exposing.
>
> Nothing is going to change so that it makes sense to have any real
> mmio-using hardware driver run on uml. The question you raise is, are
> there other classes of driver with a software-only subset that can be
> exposed on uml? And if so, would adding stub implementations of
> readb/writeb and friends actually be enough to make those work? I'm not
> aware of any, so at present I don't think the argument for implementing
> this in uml arch code is very strong. Or in other words, I don't think a
> "general solution" would be very general.

For what it's worth, QEMU had replaced all my use cases for UML in the past 
few years.  If I wanted to play with loopback mounting jffs2 I'd build a kernel 
to run under QEMU, and have that emulate the flash.

Rob
-- 
GPLv3: as worthy a successor as The Phantom Menace, as timely as Duke Nukem 
Forever, and as welcome as New Coke.
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