I've written a new version of FS-Cache and CacheFS. It's not quite complete
yet, but I thought I'd wave it in front of you.
What's changed:
(*) FS-Cache/general:
- Readpages now supported.
- Caches are now "tagged" for easier selection from multiple caches.
- Entries in one index need not have keys of the same size.
- Netfs interface simplification - page tokens no longer exist.
- Cookie definitions now belong to cookies not their parents.
- Data objects now have definitions.
- Objects can have arbitrary types other than index and data file.
- Any object can have child objects.
- Any non-index object can have data.
- Cookies aren't allocated for any uncached non-index object.
- Operations on negative cookie are dealt with in inline wrapper funcs.
- Netfs must set file size on data object before accessing pages.
(*) CacheFS:
- Now based on a single metadata tree.
- No discrete indexes.
- Journalling much simplified: wandering tree algorithm used.
- Full filesystem integrity _and_ data integrity.
- More space available for cache.
- Object entries consume one sector (512 bytes) each.
- Object entries can hold up to ~400 bytes of key and aux data.
- Objects can hold pages with index values up to 2^32 or 2^64.
- Netfs aux object information updated on disk in passing on write page.
See the patched documentation for more specific information.
What remains to be done / future developments:
(*) FS-Cache/general:
- Userspace control operations (pioctl?):
- Object pinning.
- Object space reservation.
- Object retirement.
- Allocate page(s) with no read.
- Write multiple pages.
- Use kobjects for cache tags so they can be accessed through sysfs.
- Lots of testing.
(*) CacheFS:
- Autowander timer (currently only wanders on allocator underrun, sync or
unmount).
- Tree scanner:
- Object culling to make space.
- Orphaned object deletion.
- Issuing ENOBUFS if no space can be made available.
- Use CacheFS mount as filesystem, perhaps for /tmp or ccache?
(*) CacheFiles facility (caching through files on already mounted filesystem).
The patches can be downloaded from here:
(*) http://people.redhat.com/~dhowells/cachefs/signcmp-fix-2612mm1-10.diff
Fix a signed/unsigned comparison to prevent -Wsign-compare from
complaining all over the place.
(*) http://people.redhat.com/~dhowells/cachefs/fscache-bits-2612mm1-10.diff
Some changes to the core code to enable the new stuff.
(*) http://people.redhat.com/~dhowells/cachefs/fscache-docs-2612mm1-10.diff
Updated documentation.
(*) http://people.redhat.com/~dhowells/cachefs/fscache-core-2612mm1-10.diff
FS-Cache changes.
(*) http://people.redhat.com/~dhowells/cachefs/fscache-cachefs-2612mm1-10.diff
CacheFS changes.
(*) http://people.redhat.com/~dhowells/cachefs/fscache-afs-2612mm1-10.diff
Cached AFS changes.
(*) http://people.redhat.com/~dhowells/cachefs/fscache-nfs-2612mm1-10.diff
Cached NFS changes.
These were made against 2.6.12-mm1.
And there's a debugging utility as well:
http://people.redhat.com/~dhowells/cachefs/dump-cachefs.c
This can be used to examine a block device containing a cache.
David
