fix: Dynamically create netdev arguments to correctly include commas

[John15321]

Fix excessive comma in -netdev argument

Fix the previous change, where an excessive comma was added to the -netdev argument when no port forwards were passed:

-netdev user,id=eth0,,hostfwd=tcp::2222-:22...

By dynamically creating the argument to correctly include commas.

How to use

$  ./flatcar_production_qemu.sh -M 6144 -f 25565:25565 -f 25575:25575 -f 2223:2223  -- -display curses

Testing done

Correctly starts up the machine and forwards the SSH port to 2222:

$ ./flatcar_production_qemu.sh -M 6144 -- -display curses

Correctly starts up the machine and forwards the SSH port and all of the mentioned ports in the argument:

./flatcar_production_qemu.sh -M 6144 -f 25565:25565 -f 25575:25575 -f 2223:2223  -- -display curses

• Changelog entries added in the respective changelog/ directory (user-facing change, bug fix, security fix, update)
• Inspected CI output for image differences: /boot and /usr size, packages, list files for any missing binaries, kernel modules, config files, kernel modules, etc.

[chewi]

This is fine, but another way to do it is:

-netdev user,id=eth0${QEMU_FORWARDED_PORTS:+,}${QEMU_FORWARDED_PORTS},hostfwd=tcp::"${SSH_PORT}"-:22,hostname="${VM_NAME}"

[tormath1]

Looks good, thanks for the quick fix. :)

[tormath1]

This can be moved to bugfixes section.

[John15321]

This is fine, but another way to do it is:

-netdev user,id=eth0${QEMU_FORWARDED_PORTS:+,}${QEMU_FORWARDED_PORTS},hostfwd=tcp::"${SSH_PORT}"-:22,hostname="${VM_NAME}"

I deleted this part:

# Construct the -netdev user argument dynamically
NETDEV_USER_ARGS="id=eth0,hostfwd=tcp::${SSH_PORT}-:22,hostname=${VM_NAME}"
if [ -n "${QEMU_FORWARDED_PORTS}" ]; then
    NETDEV_USER_ARGS="${NETDEV_USER_ARGS},${QEMU_FORWARDED_PORTS}"
fi

And replace the -netdev call with:

case "${VM_BOARD}" in
    amd64-usr)
        qemu-system-x86_64 \
            -name "$VM_NAME" \
            -m ${VM_MEMORY} \
            -netdev user,id=eth0${QEMU_FORWARDED_PORTS+,}${QEMU_FORWARDED_PORTS},hostfwd=tcp::"${SSH_PORT}"-:22,hostname="${VM_NAME}" \
            -device virtio-net-pci,netdev=eth0 \
            -object rng-random,filename=/dev/urandom,id=rng0 -device virtio-rng-pci,rng=rng0 \
            "$@"
        ;;
    arm64-usr)
        qemu-system-aarch64 \
            -name "$VM_NAME" \
            -m ${VM_MEMORY} \
            -netdev user,id=eth0${QEMU_FORWARDED_PORTS+,}${QEMU_FORWARDED_PORTS},hostfwd=tcp::"${SSH_PORT}"-:22,hostname="${VM_NAME}" \
            -device virtio-net-device,netdev=eth0 \
            -object rng-random,filename=/dev/urandom,id=rng0 -device virtio-rng-pci,rng=rng0 \
            "$@"
        ;;
    *) die "Unsupported arch" ;;
esac

Im not sure if Im doing something wrong here but Im getting double commas here:

./flatcar_production_qemu.sh -- -display curses
qemu-system-x86_64: -netdev user,id=eth0,,hostfwd=tcp::2222-:22,hostname=flatcar_production_qemu-4215-0-0-nightly-20250114-2100: Parameter 'id' expects an identifier
Identifiers consist of letters, digits, '-', '.', '_', starting with a letter.

[chewi]

That's my fault. I edited my comment after a few moments to add a :. Without that, it still inserts the comma when the variable is set but blank.

[github-actions]

Build action triggered: https://github.com/flatcar/scripts/actions/runs/12827137845

[John15321]

That's my fault. I edited my comment after a few moments to add a :. Without that, it still inserts the comma when the variable is set but blank.

Oh, got it, thanks! Now its working perfectly 😄

[John15321]

Thanks for the tip Chewi! I updated the PR with his changes, and ran the same commands as in the PR test description and everything seems to be working 😄

[tormath1]

LGTM. Feel free to rebase / squash your commits. Too bad we missed that at the review, maybe we should add a test case for those helpers.

This has to be backported on the alpha maintenance branch too.

[John15321]

LGTM. Feel free to rebase / squash your commits. Too bad we missed that at the review, maybe we should add a test case for those helpers.

This has to be backported on the alpha maintenance branch too.

Done, sorry I forgot to use your tip for squashing will try that next time😜

Also yeah, my fault I missed that during testing somehow. How would you guys go about creating a test for something like that?

[chewi]

I'm not sure where it would fit in our test infrastructure. I think it would be important to actually run QEMU so that you know whether the invocation is valid. Perhaps it could be started headless in the background and then terminated after a few seconds. You could then check whether the exit status was successful.

[chewi]

You wouldn't even need a real disk image because it doesn't matter whether it actually boots or not. You might need real firmware for it to start though.

[tormath1]

Cherry-picked to:

• flatcar-4214