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To: Mike Touloumtzis <miket@bluemug.com>
Cc: Jeff Garzik <jgarzik@mandrakesoft.com>, Alexander Viro <viro@math.psu.edu>,
        linux-kernel@vger.kernel.org, Linus Torvalds <torvalds@transmeta.com>,
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Subject: Re: [CFT] initramfs patch
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	<20010730140928.D20284@bluemug.com>
From: ebiederm@xmission.com (Eric W. Biederman)
Date: 31 Jul 2001 00:46:32 -0600
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Mike Touloumtzis <miket@bluemug.com> writes:

> On Mon, Jul 30, 2001 at 03:50:33PM -0500, Jeff Garzik wrote:
> > On Mon, 30 Jul 2001, Mike Touloumtzis wrote:
> > > 
> > > One thing that would make embedded systems developers very happy
> > > is the ability to map a romfs or cramfs filesystem directly from
> > > the kernel image, avoiding the extra copy necessitated by the cpio
> > > archive.  Are there problems with this approach?
> > 
> > Yes -- you need to at that point store initialized structures.  Store
> > the dcache in its unpacked state on the ROM image, etc.  That's the only
> > way to "map" a romfs directly.  Otherwise there is ALWAYS an unpacking
> > or translation step between filesystem image and in-memory image.
> > 
> > Mapping an in-memory image directly may seem like a good idea, but it is
> > really not.  ESPECIALLY for embedded folks.
> 
> I think you're misunderstanding what I propose.  I'm talking about
> having a device in /dev that would allow access to a filesystem
> image (cramfs or romfs) that would be embedded in the in-memory
> kernel image.

The current mtd drivers allow exactly this.  Having a filesystem on
your flash or rom device.  I don't think any filesystem that runs on
top of them currently supports XIP but the basic infrastructure is
there. 

Eric
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