From: "James Harper" <james@ejbdigital.com.au>
Rsync integration
Not claimed - no patches yet - Not in kernel yet
Now that we have code to efficiently find newly updated files, we need to tie it into tools such as rsync and dirvish. (For bonus points, we can even allow rsync to use btrfs's builtin checksums and, when a file has changed, tell rsync _which blocks_ inside that file have changed. Would need to work with the rsync developers on that one.)
Update rsync to preserve NOCOW file status.
Means: Make rsync work like btrfs send/receive;-) and put filesystem specific code in it. I am not sure whether this is a great idea. Most of the time you will have the same filesystem on both ends. Then you can use zfs/btrfs etc. tools. Or rsync if it's not a COW system. It is more "code polluting" than it's worth I think. And if btrfs send/receive isn't stable there is a good chance to implement an unstable rsync as well. [Slightly polemic: Later assume that rsync is running on btrfs and make it a requirement;-) (See Unix desktops which became Linux/systemd/upstart/udev/dbus/hald.. only.)] Regards Peter