Read port forwards from per-VM forwards.conf files

A QEMU config file section cannot hold more than one hostfwd entry, so
the forwards move out of the ini files into qemu/<vm>/forwards.conf, one
"LABEL HOST_PORT GUEST_PORT" rule per line. The new vmforwards.py parses
them, skips rules whose host port is taken and builds the -netdev
argument, which every launcher now passes instead of relying on a
netdev section in the ini or on -nic.

The ini files move to qemu/<vm>/config.ini and qemu/<vm>/<os>-<arch>.ini.
The *_SSH_PORT / *_RDP_PORT variables and --rdp-port / --ssh-port still
replace the host port of the SSH and RDP rules.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

run-ubuntu2604.py

@@ -3,13 +3,14 @@
 
 import os
 import platform
-import re
 import shutil
 import string
 import subprocess
 import sys
 from pathlib import Path
 
+import vmforwards
+
 script_dir = Path(__file__).resolve().parent
 env = os.environ.get
 
@@ -69,11 +70,13 @@ native_arch = normalize_arch(platform.machine())
 host_arch = normalize_arch(env("VM_IMAGE_ARCH") or native_arch)
 qemu_binary = "qemu-system-aarch64" if host_arch == "arm64" else "qemu-system-x86_64"
 qemu_config_template = Path(
-    env("UBUNTU_VM_QEMU_CONFIG") or script_dir / "qemu" / "ubuntu2604.ini")
+    env("UBUNTU_VM_QEMU_CONFIG") or script_dir / "qemu" / "ubuntu2604" / "config.ini")
 host_os = platform.system().lower()
 if host_os == "darwin" and host_arch == "amd64":
     die("amd64 guests are not supported on macOS hosts; use an arm64 image")
-qemu_platform_config = script_dir / "qemu" / f"ubuntu2604-{host_os}-{host_arch}.ini"
+qemu_platform_config = script_dir / "qemu" / "ubuntu2604" / f"{host_os}-{host_arch}.ini"
+forwards_file = Path(
+    env("UBUNTU_VM_FORWARDS") or script_dir / "qemu" / "ubuntu2604" / "forwards.conf")
 
 
 def pick_firmware(override, *candidates):
@@ -126,11 +129,13 @@ Usage: {Path(sys.argv[0]).name} [--daemon] [--download-only] [--state-dir DIR] [
 
 Start an Ubuntu 26.04 LTS cloud image virtual machine. A writable overlay is
 created in the state directory (default: vm/ubuntu2604/), so the downloaded
-base image is never modified. The VM hardware (memory, CPUs, SSH port forward,
-...) is defined in qemu/ubuntu2604.ini, which is rendered to qemu.ini in the
-state directory and loaded with QEMU's -readconfig, followed by
-qemu/ubuntu2604-<os>-<arch>.ini (os is linux or darwin, arch is amd64 or arm64). Later QEMU arguments override them, e.g.
+base image is never modified. The VM hardware (memory, CPUs, ...) is defined
+in qemu/ubuntu2604/config.ini, which is rendered to qemu.ini in the state directory
+and loaded with QEMU's -readconfig, followed by
+qemu/ubuntu2604/<os>-<arch>.ini (os is linux or darwin, arch is amd64 or arm64). Later QEMU arguments override them, e.g.
 `-- -m 4G -smp 4`.
+Host port forwards, one "LABEL HOST_PORT GUEST_PORT" rule per line, are
+read from qemu/ubuntu2604/forwards.conf.
 
 Options:
   --daemon         Run in the background while keeping the graphical window
@@ -150,7 +155,8 @@ Environment variables:
   UBUNTU_VM_UEFI_VARS      UEFI variable-store template path (auto-detected for the selected architecture)
   UBUNTU_VM_DISPLAY        QEMU display backend (default: cocoa on macOS, gtk elsewhere)
   UBUNTU_VM_QEMU_CONFIG    QEMU config template rendered into the state directory and
-                           passed to -readconfig (default: qemu/ubuntu2604.ini)
+                           passed to -readconfig (default: qemu/ubuntu2604/config.ini)
+  UBUNTU_VM_FORWARDS       Port forward file (default: qemu/ubuntu2604/forwards.conf)
 """)
 
 
@@ -266,24 +272,24 @@ except (KeyError, ValueError) as error:
     die(f"invalid placeholder in {qemu_config_template}: {error}")
 qemu_config.write_text(qemu_config_text)
 
+forwards = vmforwards.usable_forwards(vmforwards.load_forwards(forwards_file))
+
 qemu_args = [
     "-readconfig", str(qemu_config),
     "-readconfig", str(qemu_platform_config),
     # "max" is the host CPU under KVM/HVF and the fullest model under TCG.
     "-cpu", "max",
-    # The config file's [netdev] does not stop QEMU from adding its default
-    # NIC, a second user network without the SSH port forward.
+    # A config file section cannot hold two hostfwd entries, so the network
+    # that the NIC in the config file uses is defined here. -nic none stops
+    # QEMU from adding its default NIC as well.
+    "-netdev", vmforwards.netdev_argument(forwards),
     "-nic", "none",
     "-display", display_backend,
 ]
 
 print(f"Starting Ubuntu 26.04 ({host_arch}) from {qemu_config_template} "
       f"and {qemu_platform_config}.", flush=True)
-# The SSH port forward lives in the config file, e.g. hostfwd = "tcp::2225-:22".
-ssh_forward = re.search(r'hostfwd\s*=\s*"tcp:[^:"]*:(\d+)-[^:"]*:22"', qemu_config_text)
-if ssh_forward:
-    print(f"SSH is forwarded to localhost:{ssh_forward.group(1)}: "
-          f"ssh -p {ssh_forward.group(1)} guofang@localhost", flush=True)
+vmforwards.print_forwards(forwards)
 
 if daemonize:
     log_file.write_text("")