Hi all, This is a RFC-quality pass at kernel support for mapping multiple file logical blocks to the same physical block, more commonly known as reflinking. It is a single [block, refcount] tree to track the reference counts of extents of physical blocks. There's also a bunch of support code that provides the desired copy-on-write behavior, userland interfaces to reflink, query the status of, and un-reflink files. The patch set is based on the current (4.2) for-next branch plus Dave's rmap RFC patches. There are still a lot of bugs in this code; I'm not sure that I've gotten the locking and the transaction handling correct. Deadlocks and hangs due to the log being full are unfortunately common, but light exercise shows that it works well enough as a proof of concept. The ioctl interface to XFS reflink looks surprisingly like the btrfs ioctl interface <cough> -- you can reflink a file, reflink subranges of a file, or dedupe subranges of files. (Dedupe also checks file blocks, though I have a feeling it's racy.) To un-reflink a file, simply chattr +C it to mark it no-cow. xfs_fsr can be better at that, though. :) If you're going to start using this mess, you're going to want to pull my xfsprogs dev tree[1], which itself is also based on xfsprogs for-next and the userland rmap support bits. I've not had time to get reflink and rmap to work together. I've also prepared a bunch of xfstests[2] to exercise the userland interfaces. This is an extraordinary way to eat your data. Enjoy! Comments and questions are, as always, welcome. --D [1] https://github.com/djwong/xfsprogs/commits/for-next [2] https://github.com/djwong/xfstests/commits/master _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
