Seems to be broken in all archs and current kernels

[root@dhcpd156 /root]# lsmod
Module                  Size  Used by
loop                   14016   0  (autoclean)

[root@dhcpd156 /root]# losetup -e des /dev/loop0 /file
Password: 
Init (up to 16 hex digits): 
ioctl: LOOP_SET_STATUS: Invalid argument
[root@dhcpd156 /root]# 

-e des requires the crypto patch to the kernel, which we don't ship for
historical reasons. We might, if someone cares enough to put it on the
$nextversion featurelist.