How can I expose qemu-guest-agent QMP capabilities to the qmp tcp server in qemu on the same TCP socket port?

[Stefano Cappa]

Hi,

I already posted this question on stackoverflow https://stackoverflow.com/questions/68162860/how-can-i-expose-qemu-guest-agent-qmp-capabilities-to-the-qmp-tcp-server-in-qemu but I didn't receive any answer.

I re-post the question here with some news.

I'm using qemu-system-x86_64 to run a vm exposing QMP commands via TCP connection in this way:

qemu-system-x86_64 \
-smp 4 -m 4096 \
-vga std \
-display vnc=:0 \
-netdev user,id=n0 \
-device e1000,netdev=n0 \
-usb -device usb-tablet \
-qmp tcp:localhost:8124,server,nowait \
-k en-us \
-boot d \
-hda /filesystem/filesystem.img
Everything is ok, because I can send QMP commands to qemu locally via TCP socket connection on port 8124.

Then I installed qemu-guest-agent on the vm (Ubuntu 21.04 desktop) and I created the virtio ports required by the quemu-guest-agent service in this way:

qemu-system-x86_64 \
-smp 4 -m 4096 \
-vga std \
-display vnc=:0 \
-netdev user,id=n0 \
-device e1000,netdev=n0 \
-chardev socket,path=/tmp/qga.sock,server,nowait,id=qga0 \
-device virtio-serial \
-device virtserialport,chardev=qga0,name=org.qemu.guest_agent.0 \
-usb -device usb-tablet \
-qmp tcp:localhost:8124,server,nowait \
-k en-us \
-boot d \
-hda /filesystem/filesystem.img

quemu-guest-agent systemd service is up and running as expected (obviously on a local socket, not via TCP).

Now I want to see qemu-guest-agent QMP capabilities via TCP socket connection. How can I achieve this?

Based on the official guide(https://wiki.qemu.org/Features/GuestAgent) I have to change chardev in this way -chardev qga_proxy,id=qga0 \ but it's not working. It seems an obsolete info in that guide, because this command is not supported today. It throws error: qemu-system-x86_64: -chardev qga_proxy,id=qga0: 'qga_proxy' is not a valid char driver name

Which is the correct way to expose guest-agent QMP commands through TCP socket?

At the moment, I found this solution:

qemu-system-x86_64 \
-smp 4 -m 4096 \
-vga std \
-display vnc=:0 \
-netdev user,id=n0 \
-device e1000,netdev=n0 \
-chardev socket,id=qga0,port=8125,host:localhost,server,nowait \
-device virtio-serial \
-device virtserialport,chardev=qga0,name=org.qemu.guest_agent.0 \
-usb -device usb-tablet \
-qmp tcp:localhost:8124,server,nowait \
-k en-us \
-boot d \
-hda /filesystem/filesystem.img

but it opens 2 different TCP sockets on 2 different ports (8124, 8125). Is there a better way?

"Poxying" guest agent capabilities via the same qmp connection on port 8124 seems the optimal solution in my use case. Is it possibile?

Thank you.