Merge branch 'selftests-virtio_net-introduce-initial-testing-infrastructure'

Jiri Pirko says:

====================
selftests: virtio_net: introduce initial testing infrastructure

This patchset aims at introducing very basic initial infrastructure
for virtio_net testing, namely it focuses on virtio feature testing.

The first patch adds support for debugfs for virtio devices, allowing
user to filter features to pretend to be driver that is not capable
of the filtered feature.

Example:
$ cat /sys/bus/virtio/devices/virtio0/features
1110010111111111111101010000110010000000100000000000000000000000
$ echo "5" >/sys/kernel/debug/virtio/virtio0/filter_feature_add
$ cat /sys/kernel/debug/virtio/virtio0/filter_features
5
$ echo "virtio0" > /sys/bus/virtio/drivers/virtio_net/unbind
$ echo "virtio0" > /sys/bus/virtio/drivers/virtio_net/bind
$ cat /sys/bus/virtio/devices/virtio0/features
1110000111111111111101010000110010000000100000000000000000000000

Leverage that in the last patch that lays ground for virtio_net
selftests testing, including very basic F_MAC feature test.

To run this, do:
$ make -C tools/testing/selftests/ TARGETS=drivers/net/virtio_net/ run_tests

It is assumed, as with lot of other selftests in the net group,
that there are netdevices connected back-to-back. In this case,
two virtio_net devices connected back to back. If you use "tap" qemu
netdevice type, to configure this loop on a hypervisor, one may use
this script:

DEV1="$1"
DEV2="$2"

sudo tc qdisc add dev $DEV1 clsact
sudo tc qdisc add dev $DEV2 clsact
sudo tc filter add dev $DEV1 ingress protocol all pref 1 matchall action mirred egress redirect dev $DEV2
sudo tc filter add dev $DEV2 ingress protocol all pref 1 matchall action mirred egress redirect dev $DEV1
sudo ip link set $DEV1 up
sudo ip link set $DEV2 up

Another possibility is to use virtme-ng like this:
$ vng --network=loop
or directly:
$ vng --network=loop -- make -C tools/testing/selftests/ TARGETS=drivers/net/virtio_net/ run_tests

"loop" network type will take care of creating two "hubport" qemu netdevs
putting them into a single hub.

To do it manually with qemu, pass following command line options:
-nic hubport,hubid=1,id=nd0,model=virtio-net-pci
-nic hubport,hubid=1,id=nd1,model=virtio-net-pci
====================

Link: https://lore.kernel.org/r/20240424104049.3935572-1-jiri@resnulli.us
Signed-off-by: Paolo Abeni <pabeni@redhat.com>