test(net): add test for tap offload features

This is a regression test for the following fix:

commit a9e5f13
Author: Nikita Kalyazin <[email protected]>
Date:   Mon Sep 30 13:05:28 2024 +0000

    fix(net): set tap offload features on restore

The test verifies that tap offload features are configured for both
booted and restored VMs.

Signed-off-by: Nikita Kalyazin <[email protected]>

Author: kalyazin

tests/host_tools/udp_offload.py

@@ -0,0 +1,57 @@
+# Copyright 2024 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+# SPDX-License-Identifier: Apache-2.0
+"""
+A utility for sending a UDP message with UDP oflload enabled.
+
+Inspired by the "TUN_F_CSUM is a must" chapter
+in https://blog.cloudflare.com/fr-fr/virtual-networking-101-understanding-tap/
+by Cloudflare.
+"""
+
+import socket
+import sys
+
+
+def eprint(*args, **kwargs):
+    print(*args, file=sys.stderr, **kwargs)
+
+
+# Define SOL_UDP and UDP_SEGMENT if not defined in the system headers
+try:
+    from socket import SOL_UDP, UDP_SEGMENT
+except ImportError:
+    SOL_UDP = 17  # Protocol number for UDP
+    UDP_SEGMENT = 103  # Option code for UDP segmentation (non-standard)
+
+# Get the IP and port from command-line arguments
+if len(sys.argv) != 3:
+    eprint("Usage: python3 udp_offload.py <ip_address> <port>")
+    sys.exit(1)
+
+ip_address = sys.argv[1]
+port = int(sys.argv[2])
+
+# Create a UDP socket
+sockfd = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+
+# Set the UDP segmentation option (UDP_SEGMENT) to 1400 bytes
+optval = 1400
+try:
+    sockfd.setsockopt(SOL_UDP, UDP_SEGMENT, optval)
+except (AttributeError, PermissionError):
+    eprint("Unable to set UDP_SEGMENT option")
+    sys.exit(1)
+
+# Set the destination address and port
+servaddr = (ip_address, port)
+
+# Send the message to the destination address
+message = b"x"
+try:
+    sockfd.sendto(message, servaddr)
+    print("Message sent successfully")
+except socket.error as e:
+    eprint(f"Error sending message: {e}")
+    exit(1)
+
+sockfd.close()

tests/integration_tests/functional/test_net.py

@@ -78,3 +78,56 @@ def test_multi_queue_unsupported(uvm_plain):
             host_dev_name=tapname,
             guest_mac="AA:FC:00:00:00:01",
         )
+
+
+def run_udp_offload_test(vm):
+    """
+    - Start a socat UDP server in the guest.
+    - Try to send a UDP message with UDP offload enabled.
+
+    If tap offload features are not configured, an attempt to send a message will fail with EIO "Input/output error".
+    More info (search for "TUN_F_CSUM is a must"): https://blog.cloudflare.com/fr-fr/virtual-networking-101-understanding-tap/
+    """
+    port = 81
+
+    # Start a UDP server in the guest
+    vm.ssh.check_output(f"nohup socat UDP-LISTEN:{port} - > /dev/null 2>&1 &")
+
+    # Try to send a UDP message from host with UDP offload enabled
+    cmd = f"ip netns exec {vm.ssh_iface().netns} python3 ./host_tools/udp_offload.py {vm.ssh_iface().host} {port}"
+    ret = utils.run_cmd(cmd)
+
+    # Check that the transmission was successful
+    assert ret.returncode == 0, f"{ret.stdout=} {ret.stderr=}"
+
+
+def test_tap_offload_booted(uvm_plain_any):
+    """
+    Verify that tap offload features are configured for a booted VM.
+    """
+    vm = uvm_plain_any
+    vm.spawn()
+    vm.basic_config()
+    vm.add_net_iface()
+    vm.start()
+
+    run_udp_offload_test(vm)
+
+
+def test_tap_offload_restored(microvm_factory, guest_kernel, rootfs_ubuntu_22):
+    """
+    Verify that tap offload features are configured for a restored VM.
+    """
+    src = microvm_factory.build(guest_kernel, rootfs_ubuntu_22, monitor_memory=False)
+    src.spawn()
+    src.basic_config()
+    src.add_net_iface()
+    src.start()
+    snapshot = src.snapshot_full()
+    src.kill()
+
+    dst = microvm_factory.build()
+    dst.spawn()
+    dst.restore_from_snapshot(snapshot, resume=True)
+
+    run_udp_offload_test(dst)