Re: [PATCH v5] tests/functional: add a vfio-user smoke test

[Thomas Huth <thuth@redhat.com>]

  Hi!

On 11/09/2025 16.22, John Levon wrote:
> From: Mark Cave-Ayland <mark.caveayland@nutanix.com>
> 
> Add a basic test of the vfio-user PCI client implementation.
> 
> Co-authored-by: John Levon <john.levon@nutanix.com>
> Signed-off-by: Mark Cave-Ayland <mark.caveayland@nutanix.com>
> Signed-off-by: John Levon <john.levon@nutanix.com>
> ---
...
> diff --git a/tests/functional/x86_64/test_vfio_user_client.py b/tests/functional/x86_64/test_vfio_user_client.py
> new file mode 100755
> index 0000000000..1e4c5bc875
> --- /dev/null
> +++ b/tests/functional/x86_64/test_vfio_user_client.py
> @@ -0,0 +1,197 @@
> +#!/usr/bin/env python3
> +#
> +# Copyright (c) 2025 Nutanix, Inc.
> +#
> +# Author:
> +#  Mark Cave-Ayland <mark.caveayland@nutanix.com>
> +#  John Levon <john.levon@nutanix.com>
> +#
> +# SPDX-License-Identifier: GPL-2.0-or-later
> +"""
> +Check basic vfio-user-pci client functionality. The test starts two VMs:
> +
> +    - the server VM runs the libvfio-user "gpio" example server inside it,
> +      piping vfio-user traffic between a local UNIX socket and a virtio-serial
> +      port. On the host, the virtio-serial port is backed by a local socket.
> +
> +    - the client VM loads the gpio-pci-idio-16 kernel module, with the
> +      vfio-user client connecting to the above local UNIX socket.
> +
> +This way, we don't depend on trying to run a vfio-user server on the host
> +itself.
> +
> +Once both VMs are running, we run some basic configuration on the gpio device
> +and verify that the server is logging the expected out. As this is consistent
> +given the same VM images, we just do a simple direct comparison.
> +"""

I'm not a python expert, but I guess it would make sense to move that 
description block next to the "class VfioUserClient(QemuSystemTest):" line 
so that it's the description for the class? (that would fix the "Missing 
class docstring" that you get when using "pylint" on your code)

> +import difflib
> +import logging
> +import os
> +import select
> +import shutil
> +import socket
> +import subprocess
> +import time

pylint complains:

tests/functional/x86_64/test_vfio_user_client.py:28:0: W0611: Unused import 
difflib (unused-import)
tests/functional/x86_64/test_vfio_user_client.py:29:0: W0611: Unused import 
logging (unused-import)
tests/functional/x86_64/test_vfio_user_client.py:30:0: W0611: Unused import 
os (unused-import)
tests/functional/x86_64/test_vfio_user_client.py:31:0: W0611: Unused import 
select (unused-import)
tests/functional/x86_64/test_vfio_user_client.py:32:0: W0611: Unused import 
shutil (unused-import)
tests/functional/x86_64/test_vfio_user_client.py:33:0: W0611: Unused import 
socket (unused-import)
tests/functional/x86_64/test_vfio_user_client.py:34:0: W0611: Unused import 
subprocess (unused-import)
tests/functional/x86_64/test_vfio_user_client.py:35:0: W0611: Unused import 
time (unused-import)

... so I think you can remove those.

> +from qemu_test import Asset
> +from qemu_test import QemuSystemTest
> +from qemu_test import exec_command

Same for "exec_command" ... you don't use it in your test here.

> +from qemu_test import exec_command_and_wait_for_pattern
> +from qemu_test import wait_for_console_pattern
> +
> +# Exact output can vary, so we just sample for some expected lines.
> +EXPECTED_SERVER_LINES = [
> +    "gpio: adding DMA region [0, 0xc0000) offset=0 flags=0x3",
> +    "gpio: devinfo flags 0x3, num_regions 9, num_irqs 5",
> +    "gpio: region_info[0] offset 0 flags 0 size 0 argsz 32",
> +    "gpio: region_info[1] offset 0 flags 0 size 0 argsz 32",
> +    "gpio: region_info[2] offset 0 flags 0x3 size 256 argsz 32",
> +    "gpio: region_info[3] offset 0 flags 0 size 0 argsz 32",
> +    "gpio: region_info[4] offset 0 flags 0 size 0 argsz 32",
> +    "gpio: region_info[5] offset 0 flags 0 size 0 argsz 32",
> +    "gpio: region_info[7] offset 0 flags 0x3 size 256 argsz 32",
> +    "gpio: region7: read 256 bytes at 0",
> +    "gpio: region7: read 0 from (0x30:4)",
> +    "gpio: cleared EROM",
> +    "gpio: I/O space enabled",
> +    "gpio: memory space enabled",
> +    "gpio: SERR# enabled",
> +    "gpio: region7: wrote 0x103 to (0x4:2)",
> +    "gpio: I/O space enabled",
> +    "gpio: memory space enabled",
> +]
> +
> +class VfioUserClient(QemuSystemTest):
> +
> +    ASSET_REPO = 'https://github.com/mcayland-ntx/libvfio-user-test'

Not sure whether that indirection works with the asset pre-caching 
mechanism? Daniel, could you comment on that?

> +    ASSET_KERNEL = Asset(
> +        f'{ASSET_REPO}/raw/refs/heads/main/images/bzImage',
> +        '40292fa6ce95d516e26bccf5974e138d0db65a6de0bc540cabae060fe9dea605'
> +    )
> +
> +    ASSET_ROOTFS = Asset(
> +        f'{ASSET_REPO}/raw/refs/heads/main/images/rootfs.ext2',
> +        'e1e3abae8aebb8e6e77f08b1c531caeacf46250c94c815655c6bbea59fc3d1c1'
> +    )
> +
> +
> +    def prepare_images(self):
> +        """Download the images for the VMs."""
> +        self.kernel_path = self.ASSET_KERNEL.fetch()
> +        self.rootfs_path = self.ASSET_ROOTFS.fetch()
> +
> +    def configure_server_vm_args(self, server_vm, sock_path):
> +        """
> +        Configuration for the server VM. Set up virtio-serial device backed by
> +        the given socket path.
> +        """
> +        server_vm.add_args('-kernel', self.kernel_path)
> +        server_vm.add_args('-append', 'console=ttyS0 root=/dev/sda')
> +        server_vm.add_args('-drive',
> +            f"file={self.rootfs_path},if=ide,format=raw,id=drv0")
> +        server_vm.add_args('-snapshot')
> +        server_vm.add_args('-chardev',
> +            f"socket,id=sock0,path={sock_path},telnet=off,server=on,wait=off")
> +        server_vm.add_args('-device', 'virtio-serial')
> +        server_vm.add_args('-device',
> +            'virtserialport,chardev=sock0,name=org.fedoraproject.port.0')
> +
> +    def configure_client_vm_args(self, client_vm, sock_path):
> +        """
> +        Configuration for the client VM. Point the vfio-user-pci device to the
> +        socket path configured above.
> +        """
> +
> +        client_vm.add_args('-kernel', self.kernel_path)
> +        client_vm.add_args('-append', 'console=ttyS0 root=/dev/sda')
> +        client_vm.add_args('-drive',
> +            f'file={self.rootfs_path},if=ide,format=raw,id=drv0')
> +        client_vm.add_args('-snapshot')
> +        client_vm.add_args('-device',
> +            '{"driver":"vfio-user-pci",' +
> +            '"socket":{"path": "%s", "type": "unix"}}' % sock_path)
> +
> +    def setup_vfio_user_pci_server(self, server_vm):
> +        """
> +        Start the libvfio-user server within the server VM, and arrange
> +        for data to shuttle between its socket and the virtio serial port.
> +        """
> +        wait_for_console_pattern(self, 'login:', None, server_vm)
> +        exec_command_and_wait_for_pattern(self, 'root', '#', None, server_vm)
> +
> +        exec_command_and_wait_for_pattern(self,
> +            'gpio-pci-idio-16 -v /tmp/vfio-user.sock >/var/tmp/gpio.out 2>&1 &',
> +            '#', None, server_vm)
> +        # wait for libvfio-user to initialize properly
> +        exec_command_and_wait_for_pattern(self, 'sleep 5', '#', None, server_vm)

Could the sleep be avoided? ... it's still a race condition (even if it's 
unlikely when you wait for 5 seconds), and always sleeping 5 seconds slows 
down the test quite a bit ...

Could you maybe poll something instead, e.g. output of "dmesg" or something 
in the file system? (sorry, I don't have any clue about vfio-user, so I 
don't know any better suggestions)

> +        exec_command_and_wait_for_pattern(self,
> +            'socat UNIX-CONNECT:/tmp/vfio-user.sock /dev/vport0p1,ignoreeof ' +
> +            ' &', '#', None, server_vm)
> +
> +    def test_vfio_user_pci(self):
> +        self.prepare_images()

Please move the "prepare_images" after the set_machine() and 
require_device() calls. Reason: set_machine() and require_device() could 
skip the test if it's not available in the qemu binary, so in that case you 
don't want to try to fetch the assets first.

> +        self.set_machine('pc')
> +        self.require_device('virtio-serial')
> +        self.require_device('vfio-user-pci')
> +
> +        sock_dir = self.socket_dir()
> +        socket_path = sock_dir.name + '/vfio-user.sock'

Better use os.path.join() instead of hard-coding slashes.

  Thanks,
   Thomas