Re: [PATCH 2.6.21] cramfs: add cramfs Linear XIP

[Jared Hulbert]

> 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)

Yes. And one more thing.  We can't assume every page in a file is XIP or not.

However, I still can't get even the existing get_xip_page() to work
for me so we are getting ahead of ourselves;)  Looking back on this
thread I realize I haven't confirmed if my cramfs_get_xip_page() gets
a page struct.  I assume that is my problem?  The UML find_iomem()
probably returns psuedo iomem with page structs.  While ioremap() does
not return with page struct backed memory.
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