backup superblocks

["BuraphaLinux Server" <buraphalinuxserver gmail com>]

Please reveal a way using the e2fsprogs tools to do this:

copy the known-good primary superblock to all backup superblocks

I accept unmounting the filesystem first.  This way I can add that
step to my shutdown scripts and avoid those new e2fscks on cleanly
unmounted filesystems that take many hours on my filesystems due to
feature flag mismatches.  I couldn't find any switch for tune2fs to
set flags on backup superblocks, it seems to only work on the primary
superblock.  I'm using e2fsprogs-1.40.6