https://bugzilla.redhat.com/show_bug.cgi?id=807905
Currently if you specify the blocksize parameter to mkfs-opts with a
btrfs filesystem, then it fails, because mkfs.btrfs interprets the -b
option as meaning filesystem size.
The first patch fixes this by disallowing blocksize (it cannot be
mapped meaningfully into btrfs parameters).
The second patch adds the full /sbin/mkfs.btrfs utility to the API.
We should eventually do the same for mke2fs.
Rich.