Re: virtio implementation?

[Rusty Russell <rusty-8n+1lVoiYb80n/F98K4Iww@public.gmane.org>]

On Tue, 2007-07-17 at 23:49 -0700, Dor Laor wrote:
> >On Tue, 2007-07-17 at 06:31 -0700, Dor Laor wrote:
> >> btw: Rusty - what do you think of virtio for the host?
> >
> >You mean backend?  For networking it makes a great deal of sense.  For
> >block it makes far less sense (COW, weird formats, etc).
> 
> I meant networking, but there are more components we can add to the
> host:
> 	- Block device can be directed into blkTap thus making the
> result both flexible and zero-copy.

	Let's avoid the term "zero-copy" since it usually indicates that the
people in the discussion can't count.  Let's further assume that kvm
changes to the lguest model where guest pages are user pages.

	AFAICT the only difference between a userspace host block driver and a
kernel host block driver is now the system call overhead, and the
difficulty of doing efficient write barriers from userspace.

> 	- backend for virtual bus that drivers virqs (or even event
> channels) into the guest

Well, kvm is going to need some method to inject interrupts, yes.
lguest already has one, but it's going to change (Carsten wants lguest
to adopt the same userspace interface as kvm).

I'm a little confused as to what we're actually trying to discuss, to be
honest.

Cheers,
Rusty.


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