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

[Christoph Hellwig <hch@infradead.org>]

On Thu, Jun 07, 2007 at 02:11:44PM -0700, Jared Hulbert wrote:
> >that even more important doesn't require pulling in
> >the whole block layer which is especially important for embedded
> >devices at the lower end of the scala.
> 
> Good point.  That is a big oversight.  Though I would prefer to handle
> that in the same fs rather than fork.

If if were actually talking about complex filesystem I'd agree.  But
the cramfs xip patch posted here touches about 2/3 of the number of
lines that cramfs has in total.  And cramfs is not exactly the best
base to start with..

> >I still think it'd be even better to just
> >hook xip support into jffs or logfs because they give you a full
> >featured flash filesystem for all needs without the complexity
> >of strictly partitioning between xip-capable and write parts
> >of your storage.
> 
> This is nirvana.   But it is not the goal of the patches in question.
> In fact there are several use cases that don't need and don't value
> the writeability and don't need therefore the overhead.  It is a long
> term goal never the less.

With the filemap_xip.c helpers adding xip support to any filesystem
is pretty trivial for the highlevel filesystem operations.  The only
interesting bit is the lowlevel code (the get_xip_page method and
the others Carsten mentioned), but we need to do these lowlevel
code in a generic and proper way anyway.

I'll try to hack up an xip prototype for jffs2 next week.