JNC wrote:
> Is there a document for 2.11 which explains in detail why they did that? I
> suspect it's actually a little more complicated than just "more address
> space".
...
> ... Switching overlays took a certain amount of
> overhead (since mapping registers had to be re-loaded); if all the networking
> code ran in supervisor mode, the supervisor mode mapping registers could be
> loaded with the right thing and just left.
That's my understanding... It allows mbufs to be mapped only
in supervisor mode...
Yea. that's a much better explanation than my glossed over 'more address
space'. It's both to get more text space (overlays weren't infinite, and being a
separate image allowed more selective communication across the interface
boundary) and to provide some separation and allow for more data to be
around easily (the BSD kernel didn't overlay data, which is technically possible
on PDP-11, but the linker didn't support it).
https://minnie.tuhs.org/PUPS/Setup/2.11bsd_setup.html says:
The networking in 2.11BSD, runs in supervisor mode, separate
from the mainstream kernel. There is room without overlaying to
hold both a SL/IP and ethernet driver. This is a major win, as
it allows the networking to maintain its mbufs in normal data
space, among other things. The networking portion of the kernel
resides in ``/netnix'', and is loaded after the kernel is
running. Since the kernel only looks for the file ``/netnix'',
it will not run if it is unable to load ``/netnix'' , sites
should build and keep a non-networking kernel in ``/'' at all
times, as a backup. NOTE: The ``/unix'' and ``/netnix''
imagines must have been created at the same time, do not
attempt to use mismatched images. The ability to have boot tell
the kernel which network image to load is on the wish list (had
to have something take the place of wishing for disklabels
;-)).
https://wfjm.github.io/home/ouxr/ shows the code path for the socket(2) syscall
Oh, that's nice.
Warner