Re: [libvirt] [PATCH 1/2] conf: add debugcon-isa chardev guest interface

On Mon, Jan 28, 2019 at 11:26:57AM +0000, Daniel P. Berrangé wrote: I'm not sure if it's that simple, if you look at the QEMU commit <c9f398e53fedb88df243e32eb9bc50fda4ec44d0> that introduced isa-debugcon there are also changes notes and apparently there are other non-ISA variants of the debugcon which are not implemented in QEMU but they exists. From what I understand it's a special device to gather debug messages from various firmwares, not only SeaBIOS, but also OVMF for example. According to our documentation: ======================================================================== Due to hystorical reasons, the serial and console elements have partially overlapping scopes. In general, both elements are used to configure one or more serial consoles to be used for interacting with the guest. The main difference between the two is that serial is used for emulated, usually native, serial consoles, whereas console is used for paravirtualized ones. Both emulated and paravirtualized serial consoles have advantages and disadvantages: - emulated serial consoles are usually initialized much earlier than paravirtualized ones, so they can be used to control the bootloader and display both firmware and early boot messages; - on several platforms, there can only be a single emulated serial console per guest but paravirtualized consoles don't suffer from the same limitation. ======================================================================== Based on that and the fact that this is a debug console for firmwares I'm more inclined to model it as <serial>. I would suggest something like this: <serial type='...'> <target type='isa-serial'> <model type='debugcon'/> or <model type='isa-debugcon'/> </serial> As Dan mentioned first 'isa-serial' is duplicated as <channel> no matter the model of the 'isa-serial' target. In order to use 'isa-serial' target we would have add some code to make sure that we duplicate the <serial> device only if the 'mode' is not set or is set to 'isa-serial'. Or if we would go with the channel: <channel type='...'> <target type='debugcon'> </channel> In case of channel we don't have to model the BUS into the type since we can pick the address type based on architecture unless the isa-debugcon works also on other architectures and not only on x86. Pavel