The following patches were made over Linus's tree. They allow users to configure the max number of ublk devices. We are currently converting users from tcmu to ublk so the 64 device limit is too small, because we have setups that have 512-1k devices. For the second patch, I've tested up to 4K devices, but was not sure if we wanted to continue to have an artificical limit or code it so the limit is based on the code. I did the latter thinking tcmu is used in some clouds and they will want to convert to ublk like we are, and they probably have larger limits than we do.
