On Tue, 2022-11-15 at 14:13 +1100, Andy Bui wrote: > On Mon, Nov 14, 2022 at 09:43:48AM -0800, Amit Shah wrote: > > > > On Sat, 2022-11-12 at 23:45 +1100, Andy Bui wrote: > > > The virtIO spec does not specify a need for a value when nominating a > > > port as a console port, yet the virtio_console driver requires the value > > > to be 1. > > > > > > Besides being a check that's not specified by the virtIO spec, I don't > > > see anywhere else in the kernel the value is used when the corresponding > > > event is VIRTIO_CONSOLE_CONSOLE_PORT. As an example QEMU also currently > > > only passes in value=1 when nominating a console port. > > > > The original virtio-console driver just had the one port, and it was, > > as the name suggests, was a console port. When we converted this > > console driver to a generic serial driver, the first port was kept as > > the console port to not break old drivers or hypervisors. I'm afraid > > we'll have to keep this bit of backward compatibility forever. > > > > I think I might be misunderstanding the exact usage of the cpkt value. > Is error'ing and not continuing with the console port nomination the intended > behaviour when value != 1? I'm guessing that there are some hypervisors out > there that set value to something not 1 and we don't want those ports to be > the console ports? I've not looked at the code in quite a bit - please bear with me as I refresh my memory. I think the backward compat concern I have here is that a really old hypervisor - one that doesn't do virtio-serial-ports yet, will not have any other messages sent from the host, but the original console setup messages. The is_serial_port() check looks for whether hvc is initialized. It's possible hvc may not have been initialized when some control message comes in. > If this is correct I think a warning should be emitted here? Not setting the > value to 1 can exhibit undefined behaviour (at least when interpreting the > virtIO spec) and it would help hypervisor developers. Did you actually run into some issue here? Amit _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
