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Re: [Libvir] RFC: Supporting serial & parallel ports for QEMU (and improving Xen)



On Wed, May 30, 2007 at 11:18:46AM -0400, Daniel Veillard wrote:
> On Mon, May 21, 2007 at 08:18:42PM +0100, Daniel P. Berrange wrote:
> > On Mon, May 21, 2007 at 10:58:02AM +0200, Gerd Hoffmann wrote:
> > >   Hi,
> > > 
> > > >The question as ever is how to represent this in XML. For serial ports 
> > > >we'll
> > > >stick with '<console>', while parallel ports we might as well use a better
> > > >named  '<parallel>'.
> > > 
> > > Hmm, I'd prefer to use '<serial>', much less confusing in the long run. 
> > > And maybe alias '<console>' to '<serial port=0>' for compatibility.
> > 
> > There is actually one compelling reason to do this - the Xen paravirt 
> > console really isn't a true serial port. It is just a dumb text console
> > driver, so perhaps it is better to distinguish <console> from <serial>
> > with this scenario. We already use <console> for HVM too though - so
> > perhaps we should say
> > 
> >   - <parallel> - parallel ports
> >   - <serial>  - serial ports
> >   - <console>  - first text based virtual console channel
> > 
> > So, paravirt Xen would only ever have a <console> element. With fullyvirt
> > Xen the first <serial> port element would also be exposed as a <console>
> > element.
> 
>   Sounds nice to me.
> 
> > > >Next up, I think should use a 'type' attribute on this
> > > >element to determine the main way ot connecting the device, and then more
> > > >type specific attributes or sub-elements as needed. If 'type' was not 
> > > >specified then use a default of 'pty', since that gives compatability with
> > > >existing practice.
> > > 
> > > Also enumerate them somehow, so you can configure multiple of them.
> > 
> > Good point, better to have an explicit 'port' number attribute than
> > to rely on implict ordering of the devices in the XML, since there's
> > no other attribute in them giving uniqueness (cf device, or MAC in
> > disk or network).
> > 
> > > >NB, whereever there are IP addresses, hostnames can be used too, hence I
> > > >call the attriute 'addr' instead of 'ip'
> > > 
> > > s/addr/host/ + s/port/service/ to make clear that non-numeric stuff is 
> > > accepted for both?
> > >
> > > <serial type='udp' port='0'>
> > >   <sendto host='loghost' service='syslog'>
> > > </serial>
> > 
> > Sounds reasonable.
> 
>   BTW what's the status ? wondering :-)

Lots of difficult bits, but I'm starting to get onto coding it. QEMU for
example doesn't have a a good way to tell you what tty it allocated so
you have to parse stdout to olook for 'char device directed to /dev/pts/4'
which is mildly evil. That said, we already do that evilness to figure
out the monitor tty, and it should be reliable once I figure out the right
algorithm :-)

Dan.
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