Am Dienstag 23 Juni 2009 16:16:13 schrieb Paul Brook: > > 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. You can argue that virtio-console is also packet based. The input buffer can accept up to 4K in one buffer and the console code can also submit larger chunks to virtio_console. > > 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 hazzle. > > 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. How can you know, that the userspace API only has trivial differences, if the question below is not answered? > > 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 different?). > > 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. You should care, because it might have an impact if two serial lines are really the right solution for the vmchannel. One thing that I forgot: You should be warned that hvc_console sometimes can be a real PITA. A while ago I tried to change virtio_console to support more than one console and hotplug and failed to find a proper solution that can handle all the subtle console/tty register/unregister combinations. You dont want to adopt new code to fit to hvc_console - leave it in virtio_console... -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
