feat(ubridge): probe iol_bridge's TAP-port support

Whether an IOU port can terminate on a persistent TAP (iol_bridge
add_nio_tap) is a capability of its own: the tap module and that command
land independently, so a build may have one without the other. Probed on
a scratch IOL bridge with a scratch TAP — one add/delete cycle, no
iol_bridge start needed (attaching a NIO works on a stopped bridge) —
cached by binary identity, with the scratch bridge id above the per-node
id space the fabric locks (513..1024) so a probe cannot collide with a
running node. Any failure, including an old build's "Unknown command",
means unknown: IOU stays on the relay datapath.

Reported through /capabilities as ubridge_iol_tap, next to ubridge_tap.

tests/api/routes/compute/test_capabilities.py

@@ -29,7 +29,7 @@ pytestmark = pytest.mark.asyncio
 
 
 async def _no_tap_probe():
-    """The tap probe spawns uBridge — stub it out for payload assertions."""
+    """The probes spawn uBridge — stub them out for payload assertions."""
 
     return None
 
@@ -42,6 +42,7 @@ class TestCapabilitiesRoutes:
 
         monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_tc_capabilities", no_probe)
         monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_tap_support", _no_tap_probe)
+        monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_iol_tap_support", _no_tap_probe)
         response = await compute_client.get(app.url_path_for("compute:get_capabilities"))
         assert response.status_code == status.HTTP_200_OK
         assert response.json() == {
@@ -67,6 +68,7 @@ class TestCapabilitiesRoutes:
             "disk_size": psutil.disk_usage(get_default_project_directory()).total,
             "ubridge_tc": None,
             "ubridge_tap": None,
+            "ubridge_iol_tap": None,
         }
 
     async def test_get_on_gns3vm(self, app: FastAPI, compute_client: AsyncClient, on_gns3vm, monkeypatch) -> None:
@@ -76,6 +78,7 @@ class TestCapabilitiesRoutes:
 
         monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_tc_capabilities", no_probe)
         monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_tap_support", _no_tap_probe)
+        monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_iol_tap_support", _no_tap_probe)
         response = await compute_client.get(app.url_path_for("compute:get_capabilities"))
         assert response.status_code == status.HTTP_200_OK
         assert response.json() == {
@@ -101,6 +104,7 @@ class TestCapabilitiesRoutes:
             "disk_size": psutil.disk_usage(get_default_project_directory()).total,
             "ubridge_tc": None,
             "ubridge_tap": None,
+            "ubridge_iol_tap": None,
         }
 
     async def test_get_reports_ubridge_tc(self, app: FastAPI, compute_client: AsyncClient, monkeypatch) -> None:
@@ -110,6 +114,7 @@ class TestCapabilitiesRoutes:
 
         monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_tc_capabilities", fake_probe)
         monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_tap_support", _no_tap_probe)
+        monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_iol_tap_support", _no_tap_probe)
         response = await compute_client.get(app.url_path_for("compute:get_capabilities"))
         assert response.status_code == status.HTTP_200_OK
         assert response.json()["ubridge_tc"] == {
@@ -129,6 +134,22 @@ class TestCapabilitiesRoutes:
             return True
 
         monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_tap_support", fake_tap_probe)
+        monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_iol_tap_support", _no_tap_probe)
         response = await compute_client.get(app.url_path_for("compute:get_capabilities"))
         assert response.status_code == status.HTTP_200_OK
         assert response.json()["ubridge_tap"] is True
+
+    async def test_get_reports_ubridge_iol_tap(self, app: FastAPI, compute_client: AsyncClient, monkeypatch) -> None:
+        """
+        The IOL-port TAP capability is what makes an IOU node kernel-eligible,
+        so it travels with the other compute capabilities.
+        """
+
+        async def fake_iol_tap_probe():
+            return True
+
+        monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_iol_tap_support", fake_iol_tap_probe)
+        monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_tap_support", _no_tap_probe)
+        response = await compute_client.get(app.url_path_for("compute:get_capabilities"))
+        assert response.status_code == status.HTTP_200_OK
+        assert response.json()["ubridge_iol_tap"] is True

tests/compute/ubridge/test_tc_probe.py

@@ -22,7 +22,7 @@ payload: spawn a throwaway uBridge, ask once, cache by binary identity.
 import pytest
 
 from gns3server.compute.ubridge import tc_probe
-from gns3server.compute.ubridge.tc_probe import probe_tc_capabilities, probe_tap_support
+from gns3server.compute.ubridge.tc_probe import probe_iol_tap_support, probe_tc_capabilities, probe_tap_support
 from gns3server.compute.ubridge.ubridge_error import UbridgeError
 
 pytestmark = pytest.mark.asyncio
@@ -35,6 +35,7 @@ class FakeHypervisor:
 
     reply = ["netem=delay,rate;ebpf=1;cbpf=1;ebpf_modes=nth,quota,window,flow"]
     error = None
+    error_prefix = None  # fail only commands starting with this (a build missing one command)
     spawned = 0
 
     def __init__(self, project, path, working_dir, transport, host, node_id):
@@ -54,6 +55,8 @@ class FakeHypervisor:
         self.commands.append(command)
         if self.error:
             raise UbridgeError(self.error)
+        if self.error_prefix and command.startswith(self.error_prefix):
+            raise UbridgeError(f"202-Unknown command")
         if command == "tc capabilities":
             return FakeHypervisor.reply
         return ["OK"]
@@ -67,9 +70,11 @@ def probe_env(monkeypatch, tmp_path):
 
     FakeHypervisor.spawned = 0
     FakeHypervisor.error = None
+    FakeHypervisor.error_prefix = None
     FakeHypervisor.reply = ["netem=delay,rate;ebpf=1;cbpf=1;ebpf_modes=nth,quota,window,flow"]
     tc_probe._cache.clear()
     tc_probe._tap_cache.clear()
+    tc_probe._iol_tap_cache.clear()
     FakeHypervisor.last = None
     # a real file on disk: the cache is keyed on its (path, mtime, size)
     binary = tmp_path / "ubridge"
@@ -143,3 +148,48 @@ async def test_probe_tap_support_missing_binary(monkeypatch):
     monkeypatch.setattr(tc_probe.shutil, "which", lambda name: None)
     assert await probe_tap_support() is None
     assert FakeHypervisor.spawned == 0
+
+
+async def test_probe_iol_tap_support_runs_one_cycle_on_a_scratch_bridge():
+    """
+    The probe walks the exact add_nio_tap/delete_nio_tap cycle a kernel link
+    uses, on a scratch bridge whose id sits above the per-node id space, and
+    cleans up both scratch resources even when the cycle itself fails.
+    """
+
+    assert await probe_iol_tap_support() is True
+    assert FakeHypervisor.spawned == 1
+    commands = FakeHypervisor.last.commands
+    assert commands[0].startswith("iol_bridge create gns3iolprobe")
+    assert commands[0].endswith(" 1050")
+    assert commands[1].startswith("tap create gns3ita")
+    assert commands[2].startswith("iol_bridge add_nio_tap ")
+    assert commands[2].split()[-1].startswith("gns3ita")
+    assert commands[3].startswith("iol_bridge delete_nio_tap ")
+    # cleanup: bridge first (it releases the TAP fd), then the device
+    assert commands[4].startswith("iol_bridge delete ")
+    assert commands[5].startswith("tap delete ")
+
+
+async def test_probe_iol_tap_support_unknown_on_an_old_build():
+    """
+    A uBridge without iol_bridge add_nio_tap answers "Unknown command": the
+    probe reports unknown (IOU stays on the relay datapath), cleans up its
+    scratch bridge and tap, and caches the failure.
+    """
+
+    FakeHypervisor.error_prefix = "iol_bridge add_nio_tap"
+    assert await probe_iol_tap_support() is None
+    commands = FakeHypervisor.last.commands
+    assert any(c.startswith("iol_bridge delete ") for c in commands)
+    assert any(c.startswith("tap delete ") for c in commands)
+    # cached like the other probes: no respawn on every /capabilities hit
+    assert await probe_iol_tap_support() is None
+    assert FakeHypervisor.spawned == 1
+
+
+async def test_probe_iol_tap_support_missing_binary(monkeypatch):
+
+    monkeypatch.setattr(tc_probe.shutil, "which", lambda name: None)
+    assert await probe_iol_tap_support() is None
+    assert FakeHypervisor.spawned == 0

tests/controller/test_compute.py

@@ -381,7 +381,7 @@ async def test_json(compute):
         "disk_usage_percent": 0,
         "connected": True,
         "last_error": None,
-        "capabilities": {"version": "", "platform": "", "cpus": 0, "memory": 0, "disk_size": 0, "node_types": [], "ubridge_tc": None, "ubridge_tap": None},
+        "capabilities": {"version": "", "platform": "", "cpus": 0, "memory": 0, "disk_size": 0, "node_types": [], "ubridge_tc": None, "ubridge_tap": None, "ubridge_iol_tap": None},
     }
     assert compute.asdict(topology_dump=True) == {
         "compute_id": "my_compute_id",