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Re: [Qemu-devel] virtio-serial: A guest <-> host interface for simple co
Re: [Qemu-devel] virtio-serial: A guest <-> host interface for simple communication
Tue, 23 Jun 2009 15:16:13 +0100
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On Tuesday 23 June 2009, Christian Bornträger wrote:
> Am Dienstag 23 Juni 2009 14:55:52 schrieb Paul Brook:
> > > Here are two patches. One implements a virtio-serial device in qemu
> > > and the other is the driver for a guest kernel.
> > So I'll ask again. Why is this separate from virtio-console?
> I did some work on virtio-console, since kvm on s390 does not provide any
> other. I dont think we should mix two different types of devices into one
> driver. The only thing that these drivers have in common, is the fact that
> there are two virtqueues, piping data (single bytes or larger chunks). So
> you could make the same argument with the first virtio_net driver (the one
> before GSO) - which is obviously wrong. The common part of the transport is
> already factored out to virtio_ring and the transports.
virtio-net is packet based, not stream based.
> In addition there are two ABIs involved: a userspace ABI (/dev/hvc0) and a
> guest/host ABI for this console. (and virtio was not meant to be a KVM-only
> interface, that we can change all the time). David A. Wheeler's 'SLOCCount'
> gives me 141 lines of code for virtio_console.c. I am quite confident that
> the saving we could achieve by merging these two drivers is not worth the
AFAICS the functionality provided is exactly the same. The host API is
identical, and the guest userspace API only has trivial differences (which
could be eliminated with a simple udev rule). By my reading virtio-serial
makes virtio-console entirely redundant.
> Discussion about merging the console code into this distracts from the main
> problem: To get the interface and functionality right before it becomes an
> ABI (is it /dev/ttyS, network like or is it something completely
Ah, now that's a different question. I don't know what the requirements are
for the higher level vmchannel interface. However I also don't care.
Re: [Qemu-devel] virtio-serial: A guest <-> host interface for simple communication, Jamie Lokier, 2009/06/24