Re: [PATCH 2.6.21] cramfs: add cramfs Linear XIP
From: Carsten Otte
Date: Thu Jun 07 2007 - 13:08:12 EST
Christoph Hellwig wrote:
The right way to architect xip for flash-based devices is to implement
a generic get_xip_page for mtd-based devices and integrate that into
an existing flash filesystem or write a simple new flash filesystem
tailored to that use case.
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)
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.
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