Re: [Xen-devel] mini-guest io emulation

[Grzegorz Milos <gm281@xxxxxxxxx>]

As Ian mentioned some work needs to be done to make mini-os work on 64 
bit platform but the current 32 bit version of mini-os already has:
- simple scheduler (RR like)
- memory allocator (buddy allocator, and ported xmalloc build on top of 
buddy)
- xenbus implementation
I've implemented all of it last year. Obviously if we start using it for 
I/O emulation it will have to be tested more extensively, but it seemed 
to work just when I used it for my trusted domain builder.
As Aravindh mentioned it his email, we've recently added 64-bit page 
table builder, which means that the memory allocator should now work on 
64bit platform as well.
There are still a few things on TODO list we've created with Aravindh 
but I think it should be much easier to resolve those then strip Linux 
down. And I do agree with Jacob, mini-os could be useful for many other 
things then just I/O emulation.
Cheers
Gregor

> > For the "mini guest", I think it could be much easier if we
> > substantially strip down xenlinux rather than adding (eventually) a lot
> > of stuff to the current mini-os, mainly because we need probably a
> > multi-threaded run-time environment, scheduler, memory allocator, event
> > handling, drivers such as xenbus/netfront/blkfront, etc. At least, I
> > think we can use xenlinux as the development platform. For example,
> > implement the qemu-dm as a driver adding the infrastructure required
> > (e.g. small in-kernel glibc).
> It seems to me the main reason we needs threads and scheduling is to
> interact with Xenstore. A page allocator can't be that hard to
> implement. I wonder if the Xenstore API could be simplified in a way
> that does not require threading, thus making the job of implementing
> drivers in a min-os a bit simpler?
>
> My feeling is that even a stripped down Linux would take some work to
> maintain, at least if we wish to remove the need for hotplug scripts
> for driver backends and the like from the miniLinux.
>
> I have little interest in hvm guests, but having a functional mini-os
> with an extensible, perhaps oskit- or TinyOS-like, structure would be
> a huge win in a number of other situations as well. If I can I would
> like to help. If the mini-os ever gets functional, I suppose it would
> help to include it in the regression tests, to prevent the bit-rot it
> is currently suffering from.
>
> Jacob
>
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