systemd: Tagging /dev/virtio-ports/* for systemd

[Lennart Poettering]

On Wed, 06.07.11 10:22, Daniel P. Berrange (berrange at redhat.com) wrote:

> > So, I am a bit confused now after reading this:
> > 
> > http://fedoraproject.org/wiki/Features/VirtioSerial
> > 
> > How does /dev/hvcxxx relate to these virtio ports?
> > 
> > hvc ports are tagged "systemd" anyway in udev, so if this is the same
> > thing, why do we have to tag the virtio ports too?
> > 
> > Can you explain how hvc and virtio relate to each other and under which
> > kernel device names they show up in udev and how they correspond?
> 
> In QEMU, there is one PCI device "virtio-serial-pci". In QEMU's view this
> device is a bus to which we then attach zero or more 'virtconsole' or
> 'virtserialport' devices.
> 
> The 'virtconsole' device is a paravirt text console, which appears as
> /dev/hvcNNN in the guest. These are intended for interactive login and
> would be expected to run a mingetty/agetty process.

Hmm, but Unix does not really distuingish between serial ports and
ttys. So what precisely is the difference in behaviour when I have
opened a /dev/hvcXX and a /dev/vportXXX? What happens if start a getty
on /dev/vportXXX? And why couldn't I use /dev/hvcXXX for fast data
transfer, too?

Or is the only difference on the host side? i.e. the destinction between
access via pty and access via sockets?

Lennart

-- 
Lennart Poettering - Red Hat, Inc.