Re: [Qemu-devel] [PATCH] virtio-serial: PCI device for simple host <-> guest communication

[Jamie Lokier]

Amit Shah wrote:
> > Plus, having a virtio serial device and a virtio console seems  
> > unfortunate to me.  Anyway we can unify the two?  Maybe make virtio  
> > serial support hvc with a feature flag or something instead of ttyS?
> 
> Yes, it's possible. I'll look into that once I reach a point where
> virtio-serial is ready to be merged. I'll also have to look at making
> sure existing guest kernels work with the new, unified device.

One of the most useful things about a serial port is that it's so easy
for basic OS components like debuggers and bootloaders and BIOSes to
use it, with very little code, and without having to do very complex
things like initialise and enumerate PCI buses etc., and without
interference by an OS so they are useful for things like kernel
debugging and reliable debugging output.

For this reason, virtually every real machine has a simple serial
port, even if it isn't exposed on an external connector.

Are virtio-serial/virtio-console very simple to drive from guest code,
without PCI enumeration, or do they require complex initialisation and
OS cooperation?

-- Jamie