tests: re-use network namespaces

Re-using namespaces saves a whole minute of the test run:

before: 302 passed, 25 skipped in 303.29s (0:05:03)
after: 301 passed, 25 skipped in 241.77s (0:04:01)

Signed-off-by: Pablo Barbáchano <[email protected]>

tests/conftest.py

@@ -43,6 +43,7 @@
     static_cpu_templates_params,
 )
 from host_tools.metrics import get_metrics_logger
+from host_tools.network import NetNs
 
 # This codebase uses Python features available in Python 3.10 or above
 if sys.version_info < (3, 10):
@@ -245,15 +246,47 @@ def uffd_handler_paths():
     yield handlers
 
 
-@pytest.fixture()
-def microvm_factory(request, record_property, results_dir):
-    """Fixture to create microvms simply.
+@pytest.fixture(scope="session")
+def netns_factory(worker_id):
+    """A network namespace factory
 
-    In order to avoid running out of space when instantiating many microvms,
-    we remove the directory manually when the fixture is destroyed
-    (that is after every test).
-    One can comment the removal line, if it helps with debugging.
+    Network namespaces are created once per test session and re-used in subsequent tests.
     """
+    # pylint:disable=protected-access
+    # pylint:disable=too-few-public-methods
+
+    class NetNsFactory:
+        """A Network namespace factory that reuses namespaces."""
+
+        def __init__(self, prefix: str):
+            self._all = []
+            self._returned = []
+            self.prefix = prefix
+
+        def get(self, _netns_id):
+            """Get a free network namespace"""
+            if len(self._returned) > 0:
+                ns = self._returned.pop(0)
+                while ns.is_used():
+                    pass
+                return ns
+            ns = NetNs(self.prefix + str(len(self._all)))
+            # change the cleanup function so it is returned to the pool
+            ns._cleanup_orig = ns.cleanup
+            ns.cleanup = lambda: self._returned.append(ns)
+            self._all.append(ns)
+            return ns
+
+    netns_fcty = NetNsFactory(f"netns-{worker_id}-")
+    yield netns_fcty.get
+
+    for netns in netns_fcty._all:
+        netns._cleanup_orig()
+
+
+@pytest.fixture()
+def microvm_factory(request, record_property, results_dir, netns_factory):
+    """Fixture to create microvms simply."""
 
     if binary_dir := request.config.getoption("--binary-dir"):
         fc_binary_path = Path(binary_dir) / "firecracker"
@@ -266,7 +299,9 @@ def microvm_factory(request, record_property, results_dir):
 
     # We could override the chroot base like so
     # jailer_kwargs={"chroot_base": "/srv/jailo"}
-    uvm_factory = MicroVMFactory(fc_binary_path, jailer_binary_path)
+    uvm_factory = MicroVMFactory(
+        fc_binary_path, jailer_binary_path, netns_factory=netns_factory
+    )
     yield uvm_factory
 
     # if the test failed, save important files from the root of the uVM into `test_results` for troubleshooting

tests/framework/microvm.py

@@ -1057,6 +1057,7 @@ def __init__(self, fc_binary_path: Path, jailer_binary_path: Path, **kwargs):
         self.vms = []
         self.fc_binary_path = Path(fc_binary_path)
         self.jailer_binary_path = Path(jailer_binary_path)
+        self.netns_factory = kwargs.pop("netns_factory", net_tools.NetNs)
         self.kwargs = kwargs
 
     def build(self, kernel=None, rootfs=None, **kwargs):
@@ -1069,7 +1070,7 @@ def build(self, kernel=None, rootfs=None, **kwargs):
             jailer_binary_path=kwargs.pop(
                 "jailer_binary_path", self.jailer_binary_path
             ),
-            netns=kwargs.pop("netns", net_tools.NetNs(microvm_id)),
+            netns=kwargs.pop("netns", self.netns_factory(microvm_id)),
             **kwargs,
         )
         vm.netns.setup()

tests/host_tools/network.py

@@ -205,15 +205,13 @@ def __init__(self, name, netns, ip=None):
         It also creates a new tap device, brings it up and moves the interface
         to the specified namespace.
         """
-        # Avoid a conflict if two tests want to create the same tap device tap0
-        # in the host before moving it into its own netns
-        temp_name = "tap" + random_str(k=8)
-        utils.check_output(f"ip tuntap add mode tap name {temp_name}")
-        utils.check_output(f"ip link set {temp_name} name {name} netns {netns}")
-        if ip:
-            utils.check_output(f"ip netns exec {netns} ifconfig {name} {ip} up")
         self._name = name
         self._netns = netns
+        # Create the tap device tap0 directly in the network namespace to avoid
+        # conflicts
+        self.netns.check_output(f"ip tuntap add mode tap name {name}")
+        if ip:
+            self.netns.check_output(f"ifconfig {name} {ip} up")
 
     @property
     def name(self):
@@ -227,14 +225,10 @@ def netns(self):
 
     def set_tx_queue_len(self, tx_queue_len):
         """Set the length of the tap's TX queue."""
-        utils.check_output(
-            "ip netns exec {} ip link set {} txqueuelen {}".format(
-                self.netns, self.name, tx_queue_len
-            )
-        )
+        self.netns.check_output(f"ip link set {self.name} txqueuelen {tx_queue_len}")
 
     def __repr__(self):
-        return f"<Tap name={self.name} netns={self.netns}>"
+        return f"<Tap name={self.name} netns={self.netns.id}>"
 
 
 @dataclass(frozen=True, repr=True)
@@ -269,7 +263,7 @@ def with_id(i, netmask_len=30):
         )
 
 
-@dataclass(frozen=True, repr=True)
+@dataclass(repr=True)
 class NetNs:
     """Defines a network namespace."""
 
@@ -288,6 +282,10 @@ def cmd_prefix(self):
         """Return the jailer context netns file prefix."""
         return f"ip netns exec {self.id}"
 
+    def check_output(self, cmd: str):
+        """Run a command inside the netns."""
+        return utils.check_output(f"{self.cmd_prefix()} {cmd}")
+
     def setup(self):
         """Set up this network namespace."""
         if not self.path.exists():
@@ -304,6 +302,19 @@ def add_tap(self, name, ip):
         We assume that a Tap is always configured with the same IP.
         """
         if name not in self.taps:
-            tap = Tap(name, self.id, ip)
+            tap = Tap(name, self, ip)
             self.taps[name] = tap
         return self.taps[name]
+
+    def is_used(self):
+        """Are any of the TAPs still in use
+
+        Waits until there's no carrier signal.
+        Otherwise trying to reuse the TAP may return
+            `Resource busy (os error 16)`
+        """
+        for tap in self.taps:
+            _, stdout, _ = self.check_output(f"cat /sys/class/net/{tap}/carrier")
+            if stdout.strip() != "0":
+                return True
+        return False

tests/integration_tests/functional/test_api.py

@@ -191,15 +191,15 @@ def test_net_api_put_update_pre_boot(uvm_plain):
     test_microvm = uvm_plain
     test_microvm.spawn()
 
-    first_if_name = "first_tap"
-    tap1 = net_tools.Tap(first_if_name, test_microvm.netns.id)
+    tap1name = test_microvm.id[:8] + "tap1"
+    tap1 = net_tools.Tap(tap1name, test_microvm.netns)
     test_microvm.api.network.put(
         iface_id="1", guest_mac="06:00:00:00:00:01", host_dev_name=tap1.name
     )
 
     # Adding new network interfaces is allowed.
-    second_if_name = "second_tap"
-    tap2 = net_tools.Tap(second_if_name, test_microvm.netns.id)
+    tap2name = test_microvm.id[:8] + "tap2"
+    tap2 = net_tools.Tap(tap2name, test_microvm.netns)
     test_microvm.api.network.put(
         iface_id="2", guest_mac="07:00:00:00:00:01", host_dev_name=tap2.name
     )
@@ -209,28 +209,26 @@ def test_net_api_put_update_pre_boot(uvm_plain):
     expected_msg = f"The MAC address is already in use: {guest_mac}"
     with pytest.raises(RuntimeError, match=expected_msg):
         test_microvm.api.network.put(
-            iface_id="2", host_dev_name=second_if_name, guest_mac=guest_mac
+            iface_id="2", host_dev_name=tap2name, guest_mac=guest_mac
         )
 
     # Updates to a network interface with an available MAC are allowed.
     test_microvm.api.network.put(
-        iface_id="2", host_dev_name=second_if_name, guest_mac="08:00:00:00:00:01"
+        iface_id="2", host_dev_name=tap2name, guest_mac="08:00:00:00:00:01"
     )
 
     # Updates to a network interface with an unavailable name are not allowed.
     expected_msg = "Could not create the network device"
     with pytest.raises(RuntimeError, match=expected_msg):
         test_microvm.api.network.put(
-            iface_id="1", host_dev_name=second_if_name, guest_mac="06:00:00:00:00:01"
+            iface_id="1", host_dev_name=tap2name, guest_mac="06:00:00:00:00:01"
         )
 
     # Updates to a network interface with an available name are allowed.
-    iface_id = "1"
-    tapname = test_microvm.id[:8] + "tap" + iface_id
-
-    tap3 = net_tools.Tap(tapname, test_microvm.netns.id)
+    tap3name = test_microvm.id[:8] + "tap3"
+    tap3 = net_tools.Tap(tap3name, test_microvm.netns)
     test_microvm.api.network.put(
-        iface_id=iface_id, host_dev_name=tap3.name, guest_mac="06:00:00:00:00:01"
+        iface_id="3", host_dev_name=tap3.name, guest_mac="06:00:00:00:00:01"
     )
 
 
@@ -266,7 +264,7 @@ def test_api_mmds_config(uvm_plain):
         test_microvm.api.mmds_config.put(network_interfaces=["foo"])
 
     # Attach network interface.
-    tap = net_tools.Tap("tap1", test_microvm.netns.id)
+    tap = net_tools.Tap(f"tap1-{test_microvm.id[:6]}", test_microvm.netns)
     test_microvm.api.network.put(
         iface_id="1", guest_mac="06:00:00:00:00:01", host_dev_name=tap.name
     )
@@ -487,7 +485,7 @@ def test_api_put_update_post_boot(uvm_plain, io_engine):
 
     iface_id = "1"
     tapname = test_microvm.id[:8] + "tap" + iface_id
-    tap1 = net_tools.Tap(tapname, test_microvm.netns.id)
+    tap1 = net_tools.Tap(tapname, test_microvm.netns)
 
     test_microvm.api.network.put(
         iface_id=iface_id, host_dev_name=tap1.name, guest_mac="06:00:00:00:00:01"
@@ -595,7 +593,7 @@ def test_rate_limiters_api_config(uvm_plain, io_engine):
     # Test network with tx bw rate-limiting.
     iface_id = "1"
     tapname = test_microvm.id[:8] + "tap" + iface_id
-    tap1 = net_tools.Tap(tapname, test_microvm.netns.id)
+    tap1 = net_tools.Tap(tapname, test_microvm.netns)
 
     test_microvm.api.network.put(
         iface_id=iface_id,
@@ -607,7 +605,7 @@ def test_rate_limiters_api_config(uvm_plain, io_engine):
     # Test network with rx bw rate-limiting.
     iface_id = "2"
     tapname = test_microvm.id[:8] + "tap" + iface_id
-    tap2 = net_tools.Tap(tapname, test_microvm.netns.id)
+    tap2 = net_tools.Tap(tapname, test_microvm.netns)
     test_microvm.api.network.put(
         iface_id=iface_id,
         guest_mac="06:00:00:00:00:02",
@@ -618,7 +616,7 @@ def test_rate_limiters_api_config(uvm_plain, io_engine):
     # Test network with tx and rx bw and ops rate-limiting.
     iface_id = "3"
     tapname = test_microvm.id[:8] + "tap" + iface_id
-    tap3 = net_tools.Tap(tapname, test_microvm.netns.id)
+    tap3 = net_tools.Tap(tapname, test_microvm.netns)
     test_microvm.api.network.put(
         iface_id=iface_id,
         guest_mac="06:00:00:00:00:03",
@@ -665,7 +663,7 @@ def test_api_patch_pre_boot(uvm_plain, io_engine):
 
     iface_id = "1"
     tapname = test_microvm.id[:8] + "tap" + iface_id
-    tap1 = net_tools.Tap(tapname, test_microvm.netns.id)
+    tap1 = net_tools.Tap(tapname, test_microvm.netns)
     test_microvm.api.network.put(
         iface_id=iface_id, host_dev_name=tap1.name, guest_mac="06:00:00:00:00:01"
     )
@@ -714,7 +712,7 @@ def test_negative_api_patch_post_boot(uvm_plain, io_engine):
 
     iface_id = "1"
     tapname = test_microvm.id[:8] + "tap" + iface_id
-    tap1 = net_tools.Tap(tapname, test_microvm.netns.id)
+    tap1 = net_tools.Tap(tapname, test_microvm.netns)
     test_microvm.api.network.put(
         iface_id=iface_id, host_dev_name=tap1.name, guest_mac="06:00:00:00:00:01"
     )
@@ -1245,7 +1243,7 @@ def test_get_full_config(uvm_plain):
     # Add a net device.
     iface_id = "1"
     tapname = test_microvm.id[:8] + "tap" + iface_id
-    tap1 = net_tools.Tap(tapname, test_microvm.netns.id)
+    tap1 = net_tools.Tap(tapname, test_microvm.netns)
     guest_mac = "06:00:00:00:00:01"
     tx_rl = {
         "bandwidth": {"size": 1000000, "refill_time": 100, "one_time_burst": None},

tests/integration_tests/functional/test_net.py

@@ -83,6 +83,9 @@ def test_multi_queue_unsupported(uvm_plain):
             guest_mac="AA:FC:00:00:00:01",
         )
 
+    # clean TAP device
+    utils.run_cmd(f"{microvm.netns.cmd_prefix()} ip link del name {tapname}")
+
 
 @pytest.fixture
 def uvm_any(microvm_factory, uvm_ctor, guest_kernel, rootfs):