Guest (Linux/Windows) <--> Host (Linux) stdout redirection

Let's start with the console app. There is an existing mechanism of virtio-serial ports and consoles over virtio serial.

On the host side, you can bind virtio-serial port to chardev that can even be stdout. Examples:

• https://stackoverflow.com/questions/68277557/qemu-virtio-virtconsole-devices-explained
• https://fedoraproject.org/wiki/Features/VirtioSerial

On the Windows guest side, you will need to write some app that redirects the console to the virtio-serial port. Examples of the port usage can be found in qemu-ga (guest agent): https://github.com/qemu/qemu/blob/master/qga/channel-win32.c#L283

On the Linux guest side, console ports will be available as /dev/hvc* or /dev/vpor* devices depending on the command line.

Regarding config from host to guest. It can be using the same or another virtio-serial port as well.