Merge branch 'ynl-tests'

Jakub Kicinski says:

====================
selftests: net: groundwork for YNL-based tests

Currently the options for writing networking tests are C, bash or
some mix of the two. YAML/Netlink gives us the ability to easily
interface with Netlink in higher level laguages. In particular,
there is a Python library already available in tree, under tools/net.
Add the scaffolding which allows writing tests using this library.

The "scaffolding" is needed because the library lives under
tools/net and uses YAML files from under Documentation/.
So we need a small amount of glue code to find those things
and add them to TEST_FILES.

This series adds both a basic SW sanity test and driver
test which can be run against netdevsim or a real device.
When I develop core code I usually test with netdevsim,
then a real device, and then a backport to Meta's kernel.
Because of the lack of integration, until now I had
to throw away the (YNL-based) test script and netdevsim code.

Running tests in tree directly:

$ ./tools/testing/selftests/net/nl_netdev.py
KTAP version 1
1..2
ok 1 nl_netdev.empty_check
ok 2 nl_netdev.lo_check
# Totals: pass:2 fail:0 xfail:0 xpass:0 skip:0 error:0

in tree via make:

$ make -C tools/testing/selftests/ TARGETS=net \
TEST_PROGS=nl_netdev.py TEST_GEN_PROGS="" run_tests
[ ... ]

and installed externally, all seem to work:

$ make -C tools/testing/selftests/ TARGETS=net \
install INSTALL_PATH=/tmp/ksft-net
$ /tmp/ksft-net/run_kselftest.sh -t net:nl_netdev.py
[ ... ]

For driver tests I followed the lead of net/forwarding and
get the device name from env and/or a config file.

v3:
- fix up netdevsim C
- various small nits in other patches (see changelog in patches)
v2: https://lore.kernel.org/all/[e-mail]/
- don't add to TARGETS, create a deperate variable with deps
- support and use with
- support and use passing arguments to tests
v1: https://lore.kernel.org/all/[e-mail]/
====================

Signed-off-by: David S. Miller <[e-mail]>

drivers/net/netdevsim/ethtool.c

···
 	return 0;
 }
 
+static void
+nsim_get_fec_stats(struct net_device *dev, struct ethtool_fec_stats *fec_stats)
+{
+	fec_stats->corrected_blocks.total = 123;
+	fec_stats->uncorrectable_blocks.total = 4;
+}
+
 static int nsim_get_ts_info(struct net_device *dev,
 			    struct ethtool_ts_info *info)
 {
···
 	.set_channels			= nsim_set_channels,
 	.get_fecparam			= nsim_get_fecparam,
 	.set_fecparam			= nsim_set_fecparam,
+	.get_fec_stats			= nsim_get_fec_stats,
 	.get_ts_info			= nsim_get_ts_info,
 };
 
···
 	ns->netdev->ethtool_ops = &nsim_ethtool_ops;
 
 	nsim_ethtool_ring_init(ns);
+
+	ns->ethtool.pauseparam.report_stats_rx = true;
+	ns->ethtool.pauseparam.report_stats_tx = true;
 
 	ns->ethtool.fec.fec = ETHTOOL_FEC_NONE;
 	ns->ethtool.fec.active_fec = ETHTOOL_FEC_NONE;

drivers/net/netdevsim/netdev.c

···
 #include <linux/module.h>
 #include <linux/netdevice.h>
 #include <linux/slab.h>
+#include <net/netdev_queues.h>
 #include <net/netlink.h>
 #include <net/pkt_cls.h>
 #include <net/rtnetlink.h>
···
 	.ndo_set_features	= nsim_set_features,
 };
 
+/* We don't have true per-queue stats, yet, so do some random fakery here.
+ * Only report stuff for queue 0.
+ */
+static void nsim_get_queue_stats_rx(struct net_device *dev, int idx,
+				    struct netdev_queue_stats_rx *stats)
+{
+	struct rtnl_link_stats64 rtstats = {};
+
+	if (!idx)
+		nsim_get_stats64(dev, &rtstats);
+
+	stats->packets = rtstats.rx_packets - !!rtstats.rx_packets;
+	stats->bytes = rtstats.rx_bytes;
+}
+
+static void nsim_get_queue_stats_tx(struct net_device *dev, int idx,
+				    struct netdev_queue_stats_tx *stats)
+{
+	struct rtnl_link_stats64 rtstats = {};
+
+	if (!idx)
+		nsim_get_stats64(dev, &rtstats);
+
+	stats->packets = rtstats.tx_packets - !!rtstats.tx_packets;
+	stats->bytes = rtstats.tx_bytes;
+}
+
+static void nsim_get_base_stats(struct net_device *dev,
+				struct netdev_queue_stats_rx *rx,
+				struct netdev_queue_stats_tx *tx)
+{
+	struct rtnl_link_stats64 rtstats = {};
+
+	nsim_get_stats64(dev, &rtstats);
+
+	rx->packets = !!rtstats.rx_packets;
+	rx->bytes = 0;
+	tx->packets = !!rtstats.tx_packets;
+	tx->bytes = 0;
+}
+
+static const struct netdev_stat_ops nsim_stat_ops = {
+	.get_queue_stats_tx	= nsim_get_queue_stats_tx,
+	.get_queue_stats_rx	= nsim_get_queue_stats_rx,
+	.get_base_stats		= nsim_get_base_stats,
+};
+
 static void nsim_setup(struct net_device *dev)
 {
 	ether_setup(dev);
···
 
 	ns->phc = phc;
 	ns->netdev->netdev_ops = &nsim_netdev_ops;
+	ns->netdev->stat_ops = &nsim_stat_ops;
 
 	err = nsim_udp_tunnels_info_create(ns->nsim_dev, ns->netdev);
 	if (err)

tools/testing/selftests/Makefile

···
 TARGETS += dmabuf-heaps
 TARGETS += drivers/dma-buf
 TARGETS += drivers/s390x/uvdevice
+TARGETS += drivers/net
 TARGETS += drivers/net/bonding
 TARGETS += drivers/net/team
 TARGETS += dt
···
 
 TARGETS_HOTPLUG = cpu-hotplug
 TARGETS_HOTPLUG += memory-hotplug
+
+# Networking tests want the net/lib target, include it automatically
+ifneq ($(filter net drivers/net,$(TARGETS)),)
+ifeq ($(filter net/lib,$(TARGETS)),)
+	INSTALL_DEP_TARGETS := net/lib
+endif
+endif
 
 # User can optionally provide a TARGETS skiplist.  By default we skip
 # BPF since it has cutting edge build time dependencies which require
···
 	install -m 744 run_kselftest.sh $(INSTALL_PATH)/
 	rm -f $(TEST_LIST)
 	@ret=1;	\
-	for TARGET in $(TARGETS); do \
+	for TARGET in $(TARGETS) $(INSTALL_DEP_TARGETS); do \
 		BUILD_TARGET=$$BUILD/$$TARGET;	\
 		$(MAKE) OUTPUT=$$BUILD_TARGET -C $$TARGET install \
 				INSTALL_PATH=$(INSTALL_PATH)/$$TARGET \

tools/testing/selftests/drivers/net/Makefile

···
+# SPDX-License-Identifier: GPL-2.0
+
+TEST_INCLUDES := $(wildcard lib/py/*.py)
+
+TEST_PROGS := stats.py
+
+include ../../lib.mk

tools/testing/selftests/drivers/net/README.rst

···
+Running tests
+=============
+
+Tests are executed within kselftest framework like any other tests.
+By default tests execute against software drivers such as netdevsim.
+All tests must support running against a real device (SW-only tests
+should instead be placed in net/ or drivers/net/netdevsim, HW-only
+tests in drivers/net/hw).
+
+Set appropriate variables to point the tests at a real device.
+
+Variables
+=========
+
+Variables can be set in the environment or by creating a net.config
+file in the same directory as this README file. Example::
+
+  $ NETIF=eth0 ./some_test.sh
+
+or::
+
+  $ cat tools/testing/selftests/drivers/net/net.config
+  # Variable set in a file
+  NETIF=eth0
+
+NETIF
+~~~~~
+
+Name of the netdevice against which the test should be executed.
+When empty or not set software devices will be used.

tools/testing/selftests/drivers/net/lib/py/__init__.py

···
+# SPDX-License-Identifier: GPL-2.0
+
+import sys
+from pathlib import Path
+
+KSFT_DIR = (Path(__file__).parent / "../../../..").resolve()
+
+try:
+    sys.path.append(KSFT_DIR.as_posix())
+    from net.lib.py import *
+except ModuleNotFoundError as e:
+    ksft_pr("Failed importing `net` library from kernel sources")
+    ksft_pr(str(e))
+    ktap_result(True, comment="SKIP")
+    sys.exit(4)
+
+from .env import *

tools/testing/selftests/drivers/net/lib/py/env.py

···
+# SPDX-License-Identifier: GPL-2.0
+
+import os
+import shlex
+from pathlib import Path
+from lib.py import ip
+from lib.py import NetdevSimDev
+
+class NetDrvEnv:
+    def __init__(self, src_path):
+        self._ns = None
+
+        self.env = os.environ.copy()
+        self._load_env_file(src_path)
+
+        if 'NETIF' in self.env:
+            self.dev = ip("link show dev " + self.env['NETIF'], json=True)[0]
+        else:
+            self._ns = NetdevSimDev()
+            self.dev = self._ns.nsims[0].dev
+        self.ifindex = self.dev['ifindex']
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, ex_type, ex_value, ex_tb):
+        """
+        __exit__ gets called at the end of a "with" block.
+        """
+        self.__del__()
+
+    def __del__(self):
+        if self._ns:
+            self._ns.remove()
+            self._ns = None
+
+    def _load_env_file(self, src_path):
+        src_dir = Path(src_path).parent.resolve()
+        if not (src_dir / "net.config").exists():
+            return
+
+        lexer = shlex.shlex(open((src_dir / "net.config").as_posix(), 'r').read())
+        k = None
+        for token in lexer:
+            if k is None:
+                k = token
+                self.env[k] = ""
+            elif token == "=":
+                pass
+            else:
+                self.env[k] = token
+                k = None

tools/testing/selftests/drivers/net/stats.py

···
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0
+
+from lib.py import ksft_run, ksft_in, ksft_true, KsftSkipEx, KsftXfailEx
+from lib.py import EthtoolFamily, NetdevFamily, RtnlFamily, NlError
+from lib.py import NetDrvEnv
+
+ethnl = EthtoolFamily()
+netfam = NetdevFamily()
+rtnl = RtnlFamily()
+
+
+def check_pause(cfg) -> None:
+    global ethnl
+
+    try:
+        ethnl.pause_get({"header": {"dev-index": cfg.ifindex}})
+    except NlError as e:
+        if e.error == 95:
+            raise KsftXfailEx("pause not supported by the device")
+        raise
+
+    data = ethnl.pause_get({"header": {"dev-index": cfg.ifindex,
+                                       "flags": {'stats'}}})
+    ksft_true(data['stats'], "driver does not report stats")
+
+
+def check_fec(cfg) -> None:
+    global ethnl
+
+    try:
+        ethnl.fec_get({"header": {"dev-index": cfg.ifindex}})
+    except NlError as e:
+        if e.error == 95:
+            raise KsftXfailEx("FEC not supported by the device")
+        raise
+
+    data = ethnl.fec_get({"header": {"dev-index": cfg.ifindex,
+                                     "flags": {'stats'}}})
+    ksft_true(data['stats'], "driver does not report stats")
+
+
+def pkt_byte_sum(cfg) -> None:
+    global netfam, rtnl
+
+    def get_qstat(test):
+        global netfam
+        stats = netfam.qstats_get({}, dump=True)
+        if stats:
+            for qs in stats:
+                if qs["ifindex"]== test.ifindex:
+                    return qs
+
+    qstat = get_qstat(cfg)
+    if qstat is None:
+        raise KsftSkipEx("qstats not supported by the device")
+
+    for key in ['tx-packets', 'tx-bytes', 'rx-packets', 'rx-bytes']:
+        ksft_in(key, qstat, "Drivers should always report basic keys")
+
+    # Compare stats, rtnl stats and qstats must match,
+    # but the interface may be up, so do a series of dumps
+    # each time the more "recent" stats must be higher or same.
+    def stat_cmp(rstat, qstat):
+        for key in ['tx-packets', 'tx-bytes', 'rx-packets', 'rx-bytes']:
+            if rstat[key] != qstat[key]:
+                return rstat[key] - qstat[key]
+        return 0
+
+    for _ in range(10):
+        rtstat = rtnl.getlink({"ifi-index": cfg.ifindex})['stats']
+        if stat_cmp(rtstat, qstat) < 0:
+            raise Exception("RTNL stats are lower, fetched later")
+        qstat = get_qstat(cfg)
+        if stat_cmp(rtstat, qstat) > 0:
+            raise Exception("Qstats are lower, fetched later")
+
+
+def main() -> None:
+    with NetDrvEnv(__file__) as cfg:
+        ksft_run([check_pause, check_fec, pkt_byte_sum],
+                 args=(cfg, ))
+
+
+if __name__ == "__main__":
+    main()

tools/testing/selftests/net/Makefile

···
 TEST_PROGS += cmsg_so_mark.sh
 TEST_PROGS += cmsg_time.sh cmsg_ipv6.sh
 TEST_PROGS += netns-name.sh
+TEST_PROGS += nl_netdev.py
 TEST_PROGS += srv6_end_dt46_l3vpn_test.sh
 TEST_PROGS += srv6_end_dt4_l3vpn_test.sh
 TEST_PROGS += srv6_end_dt6_l3vpn_test.sh

tools/testing/selftests/net/lib/Makefile

···
+# SPDX-License-Identifier: GPL-2.0
+
+TEST_FILES := ../../../../../Documentation/netlink/specs
+TEST_FILES += ../../../../net/ynl
+
+TEST_INCLUDES := $(wildcard py/*.py)
+
+include ../../lib.mk

tools/testing/selftests/net/lib/py/__init__.py

···
+# SPDX-License-Identifier: GPL-2.0
+
+from .consts import KSRC
+from .ksft import *
+from .nsim import *
+from .utils import *
+from .ynl import NlError, YnlFamily, EthtoolFamily, NetdevFamily, RtnlFamily

tools/testing/selftests/net/lib/py/consts.py

···
+# SPDX-License-Identifier: GPL-2.0
+
+import sys
+from pathlib import Path
+
+KSFT_DIR = (Path(__file__).parent / "../../..").resolve()
+KSRC = (Path(__file__).parent / "../../../../../..").resolve()
+
+KSFT_MAIN_NAME = Path(sys.argv[0]).with_suffix("").name

tools/testing/selftests/net/lib/py/ksft.py

···
+# SPDX-License-Identifier: GPL-2.0
+
+import builtins
+from .consts import KSFT_MAIN_NAME
+
+KSFT_RESULT = None
+
+
+class KsftSkipEx(Exception):
+    pass
+
+
+class KsftXfailEx(Exception):
+    pass
+
+
+def ksft_pr(*objs, **kwargs):
+    print("#", *objs, **kwargs)
+
+
+def ksft_eq(a, b, comment=""):
+    global KSFT_RESULT
+    if a != b:
+        KSFT_RESULT = False
+        ksft_pr("Check failed", a, "!=", b, comment)
+
+
+def ksft_true(a, comment=""):
+    global KSFT_RESULT
+    if not a:
+        KSFT_RESULT = False
+        ksft_pr("Check failed", a, "does not eval to True", comment)
+
+
+def ksft_in(a, b, comment=""):
+    global KSFT_RESULT
+    if a not in b:
+        KSFT_RESULT = False
+        ksft_pr("Check failed", a, "not in", b, comment)
+
+
+def ksft_ge(a, b, comment=""):
+    global KSFT_RESULT
+    if a < b:
+        KSFT_RESULT = False
+        ksft_pr("Check failed", a, "<", b, comment)
+
+
+def ktap_result(ok, cnt=1, case="", comment=""):
+    res = ""
+    if not ok:
+        res += "not "
+    res += "ok "
+    res += str(cnt) + " "
+    res += KSFT_MAIN_NAME
+    if case:
+        res += "." + str(case.__name__)
+    if comment:
+        res += " # " + comment
+    print(res)
+
+
+def ksft_run(cases, args=()):
+    totals = {"pass": 0, "fail": 0, "skip": 0, "xfail": 0}
+
+    print("KTAP version 1")
+    print("1.." + str(len(cases)))
+
+    global KSFT_RESULT
+    cnt = 0
+    for case in cases:
+        KSFT_RESULT = True
+        cnt += 1
+        try:
+            case(*args)
+        except KsftSkipEx as e:
+            ktap_result(True, cnt, case, comment="SKIP " + str(e))
+            totals['skip'] += 1
+            continue
+        except KsftXfailEx as e:
+            ktap_result(True, cnt, case, comment="XFAIL " + str(e))
+            totals['xfail'] += 1
+            continue
+        except Exception as e:
+            for line in str(e).split('\n'):
+                ksft_pr("Exception|", line)
+            ktap_result(False, cnt, case)
+            totals['fail'] += 1
+            continue
+
+        ktap_result(KSFT_RESULT, cnt, case)
+        totals['pass'] += 1
+
+    print(
+        f"# Totals: pass:{totals['pass']} fail:{totals['fail']} xfail:{totals['xfail']} xpass:0 skip:{totals['skip']} error:0"
+    )

tools/testing/selftests/net/lib/py/nsim.py

···
+# SPDX-License-Identifier: GPL-2.0
+
+import json
+import os
+import random
+import re
+import time
+from .utils import cmd, ip
+
+
+class NetdevSim:
+    """
+    Class for netdevsim netdevice and its attributes.
+    """
+
+    def __init__(self, nsimdev, port_index, ifname, ns=None):
+        # In case udev renamed the netdev to according to new schema,
+        # check if the name matches the port_index.
+        nsimnamere = re.compile(r"eni\d+np(\d+)")
+        match = nsimnamere.match(ifname)
+        if match and int(match.groups()[0]) != port_index + 1:
+            raise Exception("netdevice name mismatches the expected one")
+
+        self.nsimdev = nsimdev
+        self.port_index = port_index
+        ret = ip("-j link show dev %s" % ifname, ns=ns)
+        self.dev = json.loads(ret.stdout)[0]
+
+    def dfs_write(self, path, val):
+        self.nsimdev.dfs_write(f'ports/{self.port_index}/' + path, val)
+
+
+class NetdevSimDev:
+    """
+    Class for netdevsim bus device and its attributes.
+    """
+    @staticmethod
+    def ctrl_write(path, val):
+        fullpath = os.path.join("/sys/bus/netdevsim/", path)
+        with open(fullpath, "w") as f:
+            f.write(val)
+
+    def dfs_write(self, path, val):
+        fullpath = os.path.join(f"/sys/kernel/debug/netdevsim/netdevsim{self.addr}/", path)
+        with open(fullpath, "w") as f:
+            f.write(val)
+
+    def __init__(self, port_count=1, ns=None):
+        # nsim will spawn in init_net, we'll set to actual ns once we switch it there
+        self.ns = None
+
+        if not os.path.exists("/sys/bus/netdevsim"):
+            cmd("modprobe netdevsim")
+
+        addr = random.randrange(1 << 15)
+        while True:
+            try:
+                self.ctrl_write("new_device", "%u %u" % (addr, port_count))
+            except OSError as e:
+                if e.errno == errno.ENOSPC:
+                    addr = random.randrange(1 << 15)
+                    continue
+                raise e
+            break
+        self.addr = addr
+
+        # As probe of netdevsim device might happen from a workqueue,
+        # so wait here until all netdevs appear.
+        self.wait_for_netdevs(port_count)
+
+        if ns:
+            cmd(f"devlink dev reload netdevsim/netdevsim{addr} netns {ns.name}")
+            self.ns = ns
+
+        cmd("udevadm settle", ns=self.ns)
+        ifnames = self.get_ifnames()
+
+        self.dfs_dir = "/sys/kernel/debug/netdevsim/netdevsim%u/" % addr
+
+        self.nsims = []
+        for port_index in range(port_count):
+            self.nsims.append(NetdevSim(self, port_index, ifnames[port_index],
+                                        ns=ns))
+
+    def get_ifnames(self):
+        ifnames = []
+        listdir = cmd(f"ls /sys/bus/netdevsim/devices/netdevsim{self.addr}/net/",
+                      ns=self.ns).stdout.split()
+        for ifname in listdir:
+            ifnames.append(ifname)
+        ifnames.sort()
+        return ifnames
+
+    def wait_for_netdevs(self, port_count):
+        timeout = 5
+        timeout_start = time.time()
+
+        while True:
+            try:
+                ifnames = self.get_ifnames()
+            except FileNotFoundError as e:
+                ifnames = []
+            if len(ifnames) == port_count:
+                break
+            if time.time() < timeout_start + timeout:
+                continue
+            raise Exception("netdevices did not appear within timeout")
+
+    def remove(self):
+        self.ctrl_write("del_device", "%u" % (self.addr, ))
+
+    def remove_nsim(self, nsim):
+        self.nsims.remove(nsim)
+        self.ctrl_write("devices/netdevsim%u/del_port" % (self.addr, ),
+                        "%u" % (nsim.port_index, ))

tools/testing/selftests/net/lib/py/utils.py

···
+# SPDX-License-Identifier: GPL-2.0
+
+import json as _json
+import subprocess
+
+class cmd:
+    def __init__(self, comm, shell=True, fail=True, ns=None, background=False):
+        if ns:
+            if isinstance(ns, NetNS):
+                ns = ns.name
+            comm = f'ip netns exec {ns} ' + comm
+
+        self.stdout = None
+        self.stderr = None
+        self.ret = None
+
+        self.comm = comm
+        self.proc = subprocess.Popen(comm, shell=shell, stdout=subprocess.PIPE,
+                                     stderr=subprocess.PIPE)
+        if not background:
+            self.process(terminate=False, fail=fail)
+
+    def process(self, terminate=True, fail=None):
+        if terminate:
+            self.proc.terminate()
+        stdout, stderr = self.proc.communicate()
+        self.stdout = stdout.decode("utf-8")
+        self.stderr = stderr.decode("utf-8")
+        self.proc.stdout.close()
+        self.proc.stderr.close()
+        self.ret = self.proc.returncode
+
+        if self.proc.returncode != 0 and fail:
+            if len(stderr) > 0 and stderr[-1] == "\n":
+                stderr = stderr[:-1]
+            raise Exception("Command failed: %s\n%s" % (self.proc.args, stderr))
+
+
+def ip(args, json=None, ns=None):
+    cmd_str = "ip "
+    if json:
+        cmd_str += '-j '
+    cmd_str += args
+    cmd_obj = cmd(cmd_str, ns=ns)
+    if json:
+        return _json.loads(cmd_obj.stdout)
+    return cmd_obj

tools/testing/selftests/net/lib/py/ynl.py

···
+# SPDX-License-Identifier: GPL-2.0
+
+import sys
+from pathlib import Path
+from .consts import KSRC, KSFT_DIR
+from .ksft import ksft_pr, ktap_result
+
+# Resolve paths
+try:
+    if (KSFT_DIR / "kselftest-list.txt").exists():
+        # Running in "installed" selftests
+        tools_full_path = KSFT_DIR
+        SPEC_PATH = KSFT_DIR / "net/lib/specs"
+
+        sys.path.append(tools_full_path.as_posix())
+        from net.lib.ynl.lib import YnlFamily, NlError
+    else:
+        # Running in tree
+        tools_full_path = KSRC / "tools"
+        SPEC_PATH = KSRC / "Documentation/netlink/specs"
+
+        sys.path.append(tools_full_path.as_posix())
+        from net.ynl.lib import YnlFamily, NlError
+except ModuleNotFoundError as e:
+    ksft_pr("Failed importing `ynl` library from kernel sources")
+    ksft_pr(str(e))
+    ktap_result(True, comment="SKIP")
+    sys.exit(4)
+
+#
+# Wrapper classes, loading the right specs
+# Set schema='' to avoid jsonschema validation, it's slow
+#
+class EthtoolFamily(YnlFamily):
+    def __init__(self):
+        super().__init__((SPEC_PATH / Path('ethtool.yaml')).as_posix(),
+                         schema='')
+
+
+class RtnlFamily(YnlFamily):
+    def __init__(self):
+        super().__init__((SPEC_PATH / Path('rt_link.yaml')).as_posix(),
+                         schema='')
+
+
+class NetdevFamily(YnlFamily):
+    def __init__(self):
+        super().__init__((SPEC_PATH / Path('netdev.yaml')).as_posix(),
+                         schema='')

tools/testing/selftests/net/nl_netdev.py

···
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0
+
+from lib.py import ksft_run, ksft_pr, ksft_eq, ksft_ge, NetdevFamily
+
+
+def empty_check(nf) -> None:
+    devs = nf.dev_get({}, dump=True)
+    ksft_ge(len(devs), 1)
+
+
+def lo_check(nf) -> None:
+    lo_info = nf.dev_get({"ifindex": 1})
+    ksft_eq(len(lo_info['xdp-features']), 0)
+    ksft_eq(len(lo_info['xdp-rx-metadata-features']), 0)
+
+
+def main() -> None:
+    nf = NetdevFamily()
+    ksft_run([empty_check, lo_check], args=(nf, ))
+
+
+if __name__ == "__main__":
+    main()