Re: todo

[Chris Wright <chrisw@sous-sol.org>]

* Jeremy Fitzhardinge (jeremy@goop.org) wrote:
> Chris Wright wrote:
> > Consistently wrap paravirt ops callsites
> > 	"ugh" - mingo
> 
> Had a thought.  What if we do a kind of reverse/two-way module linkage? 
> Somehow compile each pv-op implementation like a module, and then link
> the appropriate one in at boot time.

This is very similar to something Steve was chatting with me about
this morning.  The idea he was tossing around was something a bit like
an initrd that a load_module analog could link up.  In a sense, it's
similar to the VMI ROM, with the exceptions that the ABI is just created
by the compiler from a normal mutable kernel API and it's linkage with
symbols available on both sides.

> Tricky parts: it would need two-way unresolved references between kernel
> and module, and it would need to be able to run very early in the
> kernel's life.

This is the tricky part, and where Steve and I left off.

> It would also limit us to plain old calls rather than
> any inlining (though that could be done separately).
> 
> On the upside, it removes pv_ops, and it might simplify the question of
> how normal module exports work, since by that time they would just be
> normal kernel functions.  All the calls would be normal direct calls
> rather than indirect.  And it would allow us to free the memory for the
> unused pv-ops backends.

I suspect we could free the unused backends already.  It also has one
negative side-effect, which is promoting external module code that links
with the kernel.  IOW, there's much less incentive to get code merged
if it's just a matter of linking.

thanks,
-chris