[9fans] dynamic module loading and versioning

[Michael Baldwin <michael@cibernet.com>]

> the boundary is a bit blurred on inferno, because the explicitly
> module loading there is most commonly used to load what on other
> systems would be libraries.  but the result, at least as
> implemented, has a very different feel from the shared library hell
> on unix and windows.

Aren't some of the same maintenance and versioning headaches
associated with shared libraries still there with dynamic loading of
modules?  In Inferno, occasionally the Sys module changes (just to
pick a nasty one), and that can wreak similar havoc as incompatible
shared libraries unless you have a flag day.  I've pondered playing
with the PATH string in a module header to make this less burdensome,
but I haven't seen anyone actually do it or even talk to the issue
(OK, there aren't that (m)any users of Inferno to have people to ask,
I know).

It just seems that, if for some reason I go and change a function
signature in the String module, say, isn't it a similar headache as
shared libraries to keep all the programs that use the old and new
module running and happy at the same time?  I know merely adding
functions is still compatible, but sometimes incompatible changes
must be made (int->big for file sizes and offsets comes to mind).
And to keep old and new programs not just running but compiling is a
bit of a bitch.  Has anyone thought about or addressed these issues
in Inferno or another dynamic-loading system?  Any lessons that can
be learned and brought back to the unwashed world of shared libraries?