Re: [PATCH 3/6] virtio: console: Switch to using a port bitmap for port discovery

[Amit Shah <amit.shah@redhat.com>]

On (Mon) Mar 22 2010 [14:16:32], Michael S. Tsirkin wrote:
> > > > I can't certainly predict how many ports might be needed, but I think
> > > > we'll have other ways of communication if we need > 200 ports.
> > > 
> > > If, say, 32 bytes are sufficient, let's just reserve a fixed size
> > > array and everything will be simpler?
> > 
> > Yes, 32 bytes means 256 ports. Should be OK; if not, one could add more
> > such devices and get more ports. But if I have to choose between fixing
> > the number of ports in the config space vs using the control queue for
> > the bitmap, I'll go for the latter. That's assuming we really really
> > don't want to use the config space for storing the bitmap.
> 
> I guess with control queue we also simply use message per port
> state change - would that be simpler than a bitmap?

Yes, that's how hot-unplug is done currently (before this patchset).
I'll cook up a similar version like you suggest for adding ports as
well.

> > > > > > +	port_bit = ffs(*map);
> > > > > > +	port_bit--; /* ffs returns bit location */
> 
> simple u32 port_bit = ffs(*map) - 1; not clear enough?

Well yeah; I'll just open-code it.

		Amit
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