Implement a generic restriper for Btrfs filesystem

by Ilya Dryomov for The Linux Foundation

Btrfs currently has no support for changing between different raid levels, i.e. there is no way to change filesystem raid level (neither online nor offline) other than to re-create the entire filesystem. This project aims at implementing a generic restriper for Btrfs, which would allow online raid level changing for all types of block groups.