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

[Christoph Hellwig <hch@infradead.org>]

On Wed, Jun 06, 2007 at 06:15:04PM +0200, Carsten Otte wrote:
> The clear advantage of using cramfs on embedded platforms over using the
> ext2 stuff is, that one can choose per-file whether it should be
> compressed or xip.
> The real key is, to put both our ext2 stuff and the cramfs xip on a 
> common infrastructure. They should use the same file operations and 
> adress space operations for xip files rather then replicating each 
> others bugs.
> If cramfs shall be kept simple, it might be time to fork that file 
> system. I don't see that need arise from the proposed solution. It can 
> become clean and sane with a little work on it. Look at the xip 
> extensions for ext2 for example, they don't bloat the filesystem too much.

ext2 is a multi-purpose block based filesystem and you add support for
another bit of storage.  cramfs is very specialized to storing read-only
compressed data on block devices.  The embedded people already use them
on flash which is a little dumb, but now we add even more cludge for
a non-block based access.

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.