Lacking .gitmodules file

[alxest]

When you type git submodule init, it gives me:
fatal: No url found for submodule path 'driver/linux' in .gitmodules.
This is because .gitmodules should contain the information about submodules, but it is lacking.
(e.g. https://github.com/kaist-cp/hafnium-verification/blob/hfo2/.gitmodules)
The information is lost in this commit: 4965f1b