Re: type=ioemu? (was: Re: NetBSD in an HVM instance can't see outside world)

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Thu, Sep 04, 2008 at 12:53:33PM +0200, Johan Ihren wrote:
> >>vif = [ 'mac=00:16:3d:00:00:13, bridge=bridge0, type=ioemu' ]
> >
> >This should create a tap interface in the dom0, in addition to the  
> >usual
> >xvif. Please check that the tap interface is up, and was added to  
> >bridge0
> 
> Exactly what does the "type=ioemu" stuff mean? And why is the tap  

It emulates a real networking adapter (e.g. a ne2000, or a realtek)
in the domU, instead of presenting a PV interface

> needed for networking? And what does it do in this context (i.e. I  
> know that a tap is a virtual Ethernet in the DOM0, but at least for PV  
> the xvif is all that's needed).

The emulation is done by the qemu-dm process; is uses the tap interface
to pass ethernet packets to the dom0

> 
> Googling reveals lots of Linux references of unclear relevance to  
> NetBSD/Xen so I'm a bit confused.
> 
> And, while on the subject of ioemu, I see things like:
> 
> >disk = [ 'file:/xen/windows/winxp.img,ioemu:hda,w', 'phy:/dev/ 
> >cd0a,ioemu:hdb:cdrom,r' ]
> 
> So how is that different from not using the "ioemu:" part in front of  
> the VDEV (i.e. "hda" here)?

with ioemu, qemu-dm will emulate a PIIX IDE controller. Without it you'd
have to use PV drivers in the guest.

-- 
Manuel Bouyer, LIP6, Universite Paris VI.           
Manuel.Bouyer%lip6.fr@localhost
     NetBSD: 26 ans d'experience feront toujours la difference
--