On Sat, Dec 30, 2006 at 10:12:47AM -0500, Steven M. Bellovin wrote:
> On Fri, 29 Dec 2006 22:09:35 -0600
> david l goodrich <dlg@dorkzilla.org> wrote:
> 
> > On Fri, Dec 29, 2006 at 11:02:56PM -0500, Steven M. Bellovin wrote:
> > > I'm trying to build a dom0 system (4.0beta2) with a serial console.
> > > The standard XEN3-DOM0 doesn't include a com port; however, it 
> > > includes XEN2_DOM0, which defines ISA com ports.  My machine is (and
> > > should be) ACPI, which is supported by the XEN3-DOM0 config file.
> > > Accordingly, I added 
> > > 
> > ...
> > > 
> > > I don't know why com0 is failing, unless perhaps it's because
> > > there's a cable going to it.  com1 is just a header on the
> > > motherboard.
> > 
> > All I added to XEN2_DOM0 was this:
> > com0   at isa? port 0x3f8 irq 4        # Standard PC serial port
> > 
> > and com0 worked fine for me. 
> 
> I tried adding it to my config file that #includes XEN3_DOM0; com0
> doesn't show up at probe time.  However -- and for reasons I don't
> understand -- configuring ttys to turn on /dev/console rather
> than /dev/tty00 is working properly, in that it's speaking to the com0
> serial port.  (In a message exchange a few months ago, tjls had
> suggested the opposite -- that doesn't work here.)
> 
> Anyway -- the system is functional and speaking on com0, which is what
> I want.  I'm just mystified as to *how*, unless even for dom0 it's
> being funneled through to the hypervisor which knows from grub to talk
> to the serial port.

Yes, that's exactly what's happening: com0 is used as console by
the hypervisor, and dom0 is talking to it via the xencons driver.
You can't have com0 driven by both the hypervisor and dom0 ...

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