Instead of repeatedly trying to create an overview of the various layers involved with I/O operations within Linux on whatever white-board is in the vicinity, I decided to draw one up in Draw.io that I can then update as I learn more from this fascinating world. The drawing's smaller blocks within the layers are meant to give some guidance to what is handled where, so they are definitely not complete.

So for those interested (or those that know more of it than I ever will and prepared to help me out):

I hope it isn't too far from the truth.