linux-kernel - Re: [PATCH 2.6.21] cramfs: add cramfs Linear XIP

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Message-ID: <20070607193844.GB17144@infradead.org>
Date:	Thu, 7 Jun 2007 20:38:44 +0100
From:	Christoph Hellwig <hch@...radead.org>
To:	carsteno@...ibm.com
Cc:	Christoph Hellwig <hch@...radead.org>,
	Jared Hulbert <jaredeh@...il.com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	richard.griffiths@...driver.com,
	Richard Griffiths <res07ml0@...izon.net>,
	Linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2.6.21] cramfs: add cramfs Linear XIP

On Thu, Jun 07, 2007 at 07:07:54PM +0200, Carsten Otte wrote:
> I've had a few beer long discussion with Joern Engel and David 
> Woodhouse on this one. To cut a long discussion short: the current XIP 
> infrastructure is not sufficient to be used on top of mtd. We'd need 
> some extenstions:
> - on get_xip_page() we'd need to state if we want the reference 
> read-only or read+write
> - we need a put_xip_page() to return references
> - and finally we need a callback for the referece, so that the mtd 
> driver can ask to get its reference back (in order to unmap from 
> userland when erasing a block)

And we'll need that even when using cramfs.  There's not way we'd
merge a hack where the user has to specify a physical address on
the mount command line.

> While I fully agree, that a flash filesystem using xip would be very 
> desireable, the proposed cramfs extension is a totaly different beast 
> that has its own value to me: the ability to select per file whether 
> xip or compression is more efficient.

You'd of course want all that for a full flash filesystem aswell.
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