Description of problem:  The summary says it all.  I know what the man
page says; it's just that hanging isn't an acceptable response. The
script should test for block loopback support and produce a useful
error message if it's not there.  Mkinitrd is a hidden step for
installing a kernel and if one has removed block loopback support in
building a custom kernel, it may not be until months later that one
finds it impossible to install a new kernel after hours of compilation
with no indication of what the problem is.  And it wouldn't hurt to
put a warning comment in the kernel configuration script so this
apparently useless feature won't be removed so easily.