From: Alan Cox <alan@redhat.com>

The block layer checks for -EINVAL from block layer driver ioctls.  This is
wrong - ENOTTY is unknown and some drivers correctly use this.  I suspect
for an internal ioctl 2.7 should change to -ENOIOCTLCMD and bitch about old
style returns

This is conservative fix for the 2.6 case, it keeps the bogus -EINVAL to
avoid breaking stuff