Re: [Qemu-devel] Re: virtio-serial: An interface for host-guest communication

[Amit Shah]

On (Thu) Aug 20 2009 [20:08:02], Amit Shah wrote:
> On (Thu) Aug 20 2009 [15:25:09], Daniel P. Berrange wrote:
> > On Thu, Aug 20, 2009 at 07:12:41PM +0530, Amit Shah wrote:
> > > 
> > > I've now seen some more code here and to me it looks like virtioconsole
> > > is not used on any of the guests that qemu supports. The virtio_console
> > > kernel module only works with lguest and s390 currently. There is one
> > > feature and some config values supported by the kernel module but not in
> > > qemu.
> > > 
> > > So it looks as if we have virtio-console merged but no one uses it. Is
> > > this right?
> > 
> > Nope. Grab a Fedora 11 live CD, and boot with
> > 
> >   # qemu-kvm -virtioconsole stdio -cdrom Fedora-11-i686-Live.iso  -m 500
> > 
> > Once it completes booting & logs into gnome, open a terminal and run
> > as root
> > 
> >    agetty /dev/hvc0 9600 vt100  
> > 
> > You'll get a login prompt on the host machine now.
> > 
> > What appears to not be working, is early kernel boot messages. eg, I
> > ought to be able todo
> 
> Oh; ok. So the console device is exposed only in the userspace; it's not
> used for the early boot messages and not registered early-on. That's
> only done for lguest and s390.

which, by the way, doesn't change what I wrote above: since it's not
used for earlyboot messages anyway it's not really used as a 'console'
in its real sense and so we could just replace it with the newer version
which makes it much easier for it to work with the kernel driver. Else
supporting older qemu with newer kernel driver will be difficult (if not
impossible).

> >   # qemu-kvm -virtioconsole stdio -kernel vmlinuz -initrd initrd.img \
> >       -append "console=hvc0"  -m 500
> > 
> > and see the kernel boot messages, but this doesn't work with Fedora
> > kernels at least. Not tried upstream, or looked to see if this is just
> > an oversight in the Kconfig use for Fedora kernels.

                Amit