[RFC] Splitting CacheFS into general manager and cache backend bits

[David Howells <dhowells@redhat.com>]

I've whipped up a patch to split CacheFS into two:

 (1) FS-Cache

     This is a general cache manager that the interested netfs's talk to. It
     is supplied with a number of cache backends over which it distributes the
     operations from the netfs's.

 (2) CacheFS

     This is then made into a cache backend. The act of mounting a block
     device as cachefs causes the space contained therein to be made available
     through FS-Cache.

To give you a clearer idea of what I'm thinking, this diagram might help:

	+---------+
	|         |                        +-----------+
	|   NFS   |--+                     |           |
	|         |  |                 +-->|  CacheFS  |
	+---------+  |   +----------+  |   | /dev/hda5 |
	             |   |          |  |   +-----------+
	+---------+  +-->|          |  |
	|         |      |          |--+   +-------------+
	|   AFS   |----->| FS-Cache |      |             |
	|         |      |          |----->| Cache Files |
	+---------+  +-->|          |      | /var/cache  |
	             |   |          |--+   +-------------+
	+---------+  |   +----------+  |
	|         |  |                 |   +-------------+
	|  ISOFS  |--+                 |   |             |
	|         |                    +-->| ReiserCache |
	+---------+                        | /           |
	                                   +-------------+

So, for example, you might have a block device mounted with CacheFS as one of
your backends, the traditional bunch of cache files as another backend and
some sort of Reiser4 plug-in as a third backend.

A netfs only has to be modified to take account of FS-Cache. It then shouldn't
need to be modified further to support each different type of cache.

David