On Apr 8, 2020, at 8:58 PM, Thomas Paulsen <thomas.paulsen@firemail.de> wrote:

As was suggested on the list, I’ve reached out to Peter Weinberger to better
understand the time line of the File System Switch and the 8th edition network
f>ile system.

'Introduced with System V Release 3.0, the File System Switch (FSS) architecture introduced a framework under which multiple different filesystem types could coexist in parallel.'
https://www.oreilly.com/library/view/unix-filesystems-evolution/9780471456759/chap07-sec003.html

Thanks for that link!

The SysV R3 source floats around on the web. Its FSS is very different from what is in 8th edition.

In 8th edition the switch has 11 entries (i.e. a file system is an object with 11 virtual methods).

https://github.com/Alhadis/Research-Unix-v8/blob/master/v8/usr/sys/h/conf.h

I have never really studied R3 but at quick inspection the FSS there has 27 (!) entries and seems to be more a sys call switch.

In 10th edition it is still 11 entries, although some refactoring has taken place. Also later work from Research keeps it concise: the 9P protocol from Plan 9 has 14 messages.