Subject: Re: [PATCH 12/28] virtio: console: Buffer data that comes in from the host

From: Rusty Russell <[email-masked]>
Date: Wed, 16 Dec 2009 09:25:34 +1030

On Tue, 15 Dec 2009 09:15:19 pm Amit Shah wrote:
> On (Tue) Dec 08 2009 [11:46:10], Rusty Russell wrote:
> > On Fri, 4 Dec 2009 09:32:46 pm Amit Shah wrote:
> > > On (Thu) Dec 03 2009 [09:13:25], Amit Shah wrote:
> > > > On (Thu) Dec 03 2009 [09:24:23], Rusty Russell wrote:
> > > > > On Wed, 2 Dec 2009 07:54:06 pm Amit Shah wrote:
> > > > > > On (Wed) Dec 02 2009 [14:14:20], Rusty Russell wrote:
> > > > > > > On Sat, 28 Nov 2009 05:20:35 pm Amit Shah wrote:
> > > > > > > > The console could be flooded with data from the host; handle
> > > > > > > > this situation by buffering the data.
> > > > > > > 
> > > > > > > All this complexity makes me really wonder if we should just
> > > > > > > have the host say the max # ports it will ever use, and just do this
> > > > > > > really dumbly.  Yes, it's a limitation, but it'd be much simpler.
> > > > > > 
> > > > > > As in make sure the max nr ports is less than 255 and have per-port vqs?
> > > > > > And then the buffering will be done inside the vqs themselves?
> > > > > 
> > > > > Well < 128 (two vqs per port).  The config would say (with a feature bit)
> > > > > how many vq pairs there are.
> > > > 
> > > > Sure. This was how the previous versions behaved as well.
> > > 
> > > I forgot one detail:
> > > 
> > > http://www.mail-archive.com/[email-masked]/msg06079.html
> > > 
> > > Some API changes are needed to pre-declare the number of vqs and the
> > > selectively enable them as ports get added.
> > 
> > Couldn't we make it that all vqs *exist*, they're just unused unless the
> > bitmap (or whatever) indicates?
> 
> Yes, but the current interface makes that a bit difficult: find_vqs
> needs the entire array for the callbacks. So if instead of find_vqs, we
> could have two functions,
> 
>  ret =  init_vqs(vdev, nr_vqs);
>  for (i = 0; i < nr_vqs; i += 2)
> 	enable_vqs(vdev, i, 2, callbacks, names);
> 
> this would be simplified and we can also then enabling and disabling vqs
> as ports get hot plugged / unplugged.

No, I was thinking we find_vqs them all.  We just don't put any buffers in
the unused ones.

Cheers,
Rusty.