Convert from ext2/3/4 filesystem to btrfs or rollback
btrfs-convert [options] <device>
btrfs-convert is used to convert existed ext2/3/4 to btrfs filesystem, and the original filesystem image is accessible as from separate subvolume named ext2_saved as file image.
Disable data checksum.
Ignore xattrs and ACLs.
Disable packing of small files.
Roll back to ext2fs.
set filesystem label during conversion.
use label from the converted filesystem.
btrfs-convert will return 0 if no error happened. If any problems happened, 1 will be returned.