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>

12 files changed, 479 insertions, 0 deletions

diff --git a/MAINTAINERS b/MAINTAINERS
index 209143bac37ab1..ab89edc6974d17 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -23466,6 +23466,7 @@ F:	include/linux/virtio*.h
 F:	include/linux/vringh.h
 F:	include/uapi/linux/virtio_*.h
 F:	tools/virtio/
+F:	tools/testing/selftests/drivers/net/virtio_net/
 
 VIRTIO CRYPTO DRIVER
 M:	Gonglei <arei.gonglei@huawei.com>
diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
index c17193544268aa..6284538a8184c8 100644
--- a/drivers/virtio/Kconfig
+++ b/drivers/virtio/Kconfig
@@ -178,4 +178,14 @@ config VIRTIO_DMA_SHARED_BUFFER
 	 This option adds a flavor of dma buffers that are backed by
 	 virtio resources.
 
+config VIRTIO_DEBUG
+	bool "Debug facilities"
+	depends on VIRTIO
+	help
+	  Enable this to expose debug facilities over debugfs.
+	  This allows to debug features, to see what features the device
+	  advertises and to set filter for features used by driver.
+
+	  If unsure, say N.
+
 endif # VIRTIO_MENU
diff --git a/drivers/virtio/Makefile b/drivers/virtio/Makefile
index 73ace62af44093..58b2b0489fc9d7 100644
--- a/drivers/virtio/Makefile
+++ b/drivers/virtio/Makefile
@@ -13,3 +13,4 @@ obj-$(CONFIG_VIRTIO_INPUT) += virtio_input.o
 obj-$(CONFIG_VIRTIO_VDPA) += virtio_vdpa.o
 obj-$(CONFIG_VIRTIO_MEM) += virtio_mem.o
 obj-$(CONFIG_VIRTIO_DMA_SHARED_BUFFER) += virtio_dma_buf.o
+obj-$(CONFIG_VIRTIO_DEBUG) += virtio_debug.o
diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index 9510c551dce864..b968b2aa5f4d10 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -274,6 +274,9 @@ static int virtio_dev_probe(struct device *_d)
 	else
 		dev->features = driver_features_legacy & device_features;
 
+	/* When debugging, user may filter some features by hand. */
+	virtio_debug_device_filter_features(dev);
+
 	/* Transport features always preserved to pass to finalize_features. */
 	for (i = VIRTIO_TRANSPORT_F_START; i < VIRTIO_TRANSPORT_F_END; i++)
 		if (device_features & (1ULL << i))
@@ -465,6 +468,8 @@ int register_virtio_device(struct virtio_device *dev)
 	/* Acknowledge that we've seen the device. */
 	virtio_add_status(dev, VIRTIO_CONFIG_S_ACKNOWLEDGE);
 
+	virtio_debug_device_init(dev);
+
 	/*
 	 * device_add() causes the bus infrastructure to look for a matching
 	 * driver.
@@ -496,6 +501,7 @@ void unregister_virtio_device(struct virtio_device *dev)
 	int index = dev->index; /* save for after device release */
 
 	device_unregister(&dev->dev);
+	virtio_debug_device_exit(dev);
 	ida_free(&virtio_index_ida, index);
 }
 EXPORT_SYMBOL_GPL(unregister_virtio_device);
@@ -590,11 +596,13 @@ static int virtio_init(void)
 {
 	if (bus_register(&virtio_bus) != 0)
 		panic("virtio bus registration failed");
+	virtio_debug_init();
 	return 0;
 }
 
 static void __exit virtio_exit(void)
 {
+	virtio_debug_exit();
 	bus_unregister(&virtio_bus);
 	ida_destroy(&virtio_index_ida);
 }
diff --git a/drivers/virtio/virtio_debug.c b/drivers/virtio/virtio_debug.c
new file mode 100644
index 00000000000000..95c8fc7705bb0b
--- /dev/null
+++ b/drivers/virtio/virtio_debug.c
@@ -0,0 +1,114 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <linux/virtio.h>
+#include <linux/virtio_config.h>
+#include <linux/debugfs.h>
+
+static struct dentry *virtio_debugfs_dir;
+
+static int virtio_debug_device_features_show(struct seq_file *s, void *data)
+{
+	struct virtio_device *dev = s->private;
+	u64 device_features;
+	unsigned int i;
+
+	device_features = dev->config->get_features(dev);
+	for (i = 0; i < BITS_PER_LONG_LONG; i++) {
+		if (device_features & (1ULL << i))
+			seq_printf(s, "%u\n", i);
+	}
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(virtio_debug_device_features);
+
+static int virtio_debug_filter_features_show(struct seq_file *s, void *data)
+{
+	struct virtio_device *dev = s->private;
+	unsigned int i;
+
+	for (i = 0; i < BITS_PER_LONG_LONG; i++) {
+		if (dev->debugfs_filter_features & (1ULL << i))
+			seq_printf(s, "%u\n", i);
+	}
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(virtio_debug_filter_features);
+
+static int virtio_debug_filter_features_clear(void *data, u64 val)
+{
+	struct virtio_device *dev = data;
+
+	if (val == 1)
+		dev->debugfs_filter_features = 0;
+	return 0;
+}
+
+DEFINE_DEBUGFS_ATTRIBUTE(virtio_debug_filter_features_clear_fops, NULL,
+			 virtio_debug_filter_features_clear, "%llu\n");
+
+static int virtio_debug_filter_feature_add(void *data, u64 val)
+{
+	struct virtio_device *dev = data;
+
+	if (val >= BITS_PER_LONG_LONG)
+		return -EINVAL;
+	dev->debugfs_filter_features |= BIT_ULL_MASK(val);
+	return 0;
+}
+
+DEFINE_DEBUGFS_ATTRIBUTE(virtio_debug_filter_feature_add_fops, NULL,
+			 virtio_debug_filter_feature_add, "%llu\n");
+
+static int virtio_debug_filter_feature_del(void *data, u64 val)
+{
+	struct virtio_device *dev = data;
+
+	if (val >= BITS_PER_LONG_LONG)
+		return -EINVAL;
+	dev->debugfs_filter_features &= ~BIT_ULL_MASK(val);
+	return 0;
+}
+
+DEFINE_DEBUGFS_ATTRIBUTE(virtio_debug_filter_feature_del_fops, NULL,
+			 virtio_debug_filter_feature_del, "%llu\n");
+
+void virtio_debug_device_init(struct virtio_device *dev)
+{
+	dev->debugfs_dir = debugfs_create_dir(dev_name(&dev->dev),
+					      virtio_debugfs_dir);
+	debugfs_create_file("device_features", 0400, dev->debugfs_dir, dev,
+			    &virtio_debug_device_features_fops);
+	debugfs_create_file("filter_features", 0400, dev->debugfs_dir, dev,
+			    &virtio_debug_filter_features_fops);
+	debugfs_create_file("filter_features_clear", 0200, dev->debugfs_dir, dev,
+			    &virtio_debug_filter_features_clear_fops);
+	debugfs_create_file("filter_feature_add", 0200, dev->debugfs_dir, dev,
+			    &virtio_debug_filter_feature_add_fops);
+	debugfs_create_file("filter_feature_del", 0200, dev->debugfs_dir, dev,
+			    &virtio_debug_filter_feature_del_fops);
+}
+EXPORT_SYMBOL_GPL(virtio_debug_device_init);
+
+void virtio_debug_device_filter_features(struct virtio_device *dev)
+{
+	dev->features &= ~dev->debugfs_filter_features;
+}
+EXPORT_SYMBOL_GPL(virtio_debug_device_filter_features);
+
+void virtio_debug_device_exit(struct virtio_device *dev)
+{
+	debugfs_remove_recursive(dev->debugfs_dir);
+}
+EXPORT_SYMBOL_GPL(virtio_debug_device_exit);
+
+void virtio_debug_init(void)
+{
+	virtio_debugfs_dir = debugfs_create_dir("virtio", NULL);
+}
+EXPORT_SYMBOL_GPL(virtio_debug_init);
+
+void virtio_debug_exit(void)
+{
+	debugfs_remove_recursive(virtio_debugfs_dir);
+}
+EXPORT_SYMBOL_GPL(virtio_debug_exit);
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index 26c4325aa3734e..96fea920873bff 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -126,6 +126,8 @@ struct virtio_admin_cmd {
  * @vqs: the list of virtqueues for this device.
  * @features: the features supported by both driver and device.
  * @priv: private pointer for the driver's use.
+ * @debugfs_dir: debugfs directory entry.
+ * @debugfs_filter_features: features to be filtered set by debugfs.
  */
 struct virtio_device {
 	int index;
@@ -141,6 +143,10 @@ struct virtio_device {
 	struct list_head vqs;
 	u64 features;
 	void *priv;
+#ifdef CONFIG_VIRTIO_DEBUG
+	struct dentry *debugfs_dir;
+	u64 debugfs_filter_features;
+#endif
 };
 
 #define dev_to_virtio(_dev)	container_of_const(_dev, struct virtio_device, dev)
@@ -237,4 +243,33 @@ void virtqueue_dma_sync_single_range_for_cpu(struct virtqueue *_vq, dma_addr_t a
 void virtqueue_dma_sync_single_range_for_device(struct virtqueue *_vq, dma_addr_t addr,
 						unsigned long offset, size_t size,
 						enum dma_data_direction dir);
+
+#ifdef CONFIG_VIRTIO_DEBUG
+void virtio_debug_device_init(struct virtio_device *dev);
+void virtio_debug_device_exit(struct virtio_device *dev);
+void virtio_debug_device_filter_features(struct virtio_device *dev);
+void virtio_debug_init(void);
+void virtio_debug_exit(void);
+#else
+static inline void virtio_debug_device_init(struct virtio_device *dev)
+{
+}
+
+static inline void virtio_debug_device_exit(struct virtio_device *dev)
+{
+}
+
+static inline void virtio_debug_device_filter_features(struct virtio_device *dev)
+{
+}
+
+static inline void virtio_debug_init(void)
+{
+}
+
+static inline void virtio_debug_exit(void)
+{
+}
+#endif
+
 #endif /* _LINUX_VIRTIO_H */
diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index c785b6256a452a..2c940e9c4cedfe 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -20,6 +20,7 @@ TARGETS += drivers/s390x/uvdevice
 TARGETS += drivers/net
 TARGETS += drivers/net/bonding
 TARGETS += drivers/net/team
+TARGETS += drivers/net/virtio_net
 TARGETS += dt
 TARGETS += efivarfs
 TARGETS += exec
diff --git a/tools/testing/selftests/drivers/net/virtio_net/Makefile b/tools/testing/selftests/drivers/net/virtio_net/Makefile
new file mode 100644
index 00000000000000..7ec7cd3ab2cc62
--- /dev/null
+++ b/tools/testing/selftests/drivers/net/virtio_net/Makefile
@@ -0,0 +1,15 @@
+# SPDX-License-Identifier: GPL-2.0+ OR MIT
+
+TEST_PROGS = basic_features.sh \
+        #
+
+TEST_FILES = \
+        virtio_net_common.sh \
+        #
+
+TEST_INCLUDES = \
+        ../../../net/forwarding/lib.sh \
+        ../../../net/lib.sh \
+        #
+
+include ../../../lib.mk
diff --git a/tools/testing/selftests/drivers/net/virtio_net/basic_features.sh b/tools/testing/selftests/drivers/net/virtio_net/basic_features.sh
new file mode 100755
index 00000000000000..cf8cf816ed48c4
--- /dev/null
+++ b/tools/testing/selftests/drivers/net/virtio_net/basic_features.sh
@@ -0,0 +1,131 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+# See virtio_net_common.sh comments for more details about assumed setup
+
+ALL_TESTS="
+	initial_ping_test
+	f_mac_test
+"
+
+source virtio_net_common.sh
+
+lib_dir=$(dirname "$0")
+source "$lib_dir"/../../../net/forwarding/lib.sh
+
+h1=${NETIFS[p1]}
+h2=${NETIFS[p2]}
+
+h1_create()
+{
+	simple_if_init $h1 $H1_IPV4/24 $H1_IPV6/64
+}
+
+h1_destroy()
+{
+	simple_if_fini $h1 $H1_IPV4/24 $H1_IPV6/64
+}
+
+h2_create()
+{
+	simple_if_init $h2 $H2_IPV4/24 $H2_IPV6/64
+}
+
+h2_destroy()
+{
+	simple_if_fini $h2 $H2_IPV4/24 $H2_IPV6/64
+}
+
+initial_ping_test()
+{
+	setup_cleanup
+	setup_prepare
+	ping_test $h1 $H2_IPV4 " simple"
+}
+
+f_mac_test()
+{
+	RET=0
+	local test_name="mac feature filtered"
+
+	virtio_feature_present $h1 $VIRTIO_NET_F_MAC
+	if [ $? -ne 0 ]; then
+		log_test_skip "$test_name" "Device $h1 is missing feature $VIRTIO_NET_F_MAC."
+		return 0
+	fi
+	virtio_feature_present $h1 $VIRTIO_NET_F_MAC
+	if [ $? -ne 0 ]; then
+		log_test_skip "$test_name" "Device $h2 is missing feature $VIRTIO_NET_F_MAC."
+		return 0
+	fi
+
+	setup_cleanup
+	setup_prepare
+
+	grep -q 0 /sys/class/net/$h1/addr_assign_type
+	check_err $? "Permanent address assign type for $h1 is not set"
+	grep -q 0 /sys/class/net/$h2/addr_assign_type
+	check_err $? "Permanent address assign type for $h2 is not set"
+
+	setup_cleanup
+	virtio_filter_feature_add $h1 $VIRTIO_NET_F_MAC
+	virtio_filter_feature_add $h2 $VIRTIO_NET_F_MAC
+	setup_prepare
+
+	grep -q 0 /sys/class/net/$h1/addr_assign_type
+	check_fail $? "Permanent address assign type for $h1 is set when F_MAC feature is filtered"
+	grep -q 0 /sys/class/net/$h2/addr_assign_type
+	check_fail $? "Permanent address assign type for $h2 is set when F_MAC feature is filtered"
+
+	ping_do $h1 $H2_IPV4
+	check_err $? "Ping failed"
+
+	log_test "$test_name"
+}
+
+setup_prepare()
+{
+	virtio_device_rebind $h1
+	virtio_device_rebind $h2
+	wait_for_dev $h1
+	wait_for_dev $h2
+
+	vrf_prepare
+
+	h1_create
+	h2_create
+}
+
+setup_cleanup()
+{
+	h2_destroy
+	h1_destroy
+
+	vrf_cleanup
+
+	virtio_filter_features_clear $h1
+	virtio_filter_features_clear $h2
+	virtio_device_rebind $h1
+	virtio_device_rebind $h2
+	wait_for_dev $h1
+	wait_for_dev $h2
+}
+
+cleanup()
+{
+	pre_cleanup
+	setup_cleanup
+}
+
+check_driver $h1 "virtio_net"
+check_driver $h2 "virtio_net"
+check_virtio_debugfs $h1
+check_virtio_debugfs $h2
+
+trap cleanup EXIT
+
+setup_prepare
+
+tests_run
+
+exit "$EXIT_STATUS"
diff --git a/tools/testing/selftests/drivers/net/virtio_net/config b/tools/testing/selftests/drivers/net/virtio_net/config
new file mode 100644
index 00000000000000..f35de0542b6089
--- /dev/null
+++ b/tools/testing/selftests/drivers/net/virtio_net/config
@@ -0,0 +1,2 @@
+CONFIG_VIRTIO_NET=y
+CONFIG_VIRTIO_DEBUG=y
diff --git a/tools/testing/selftests/drivers/net/virtio_net/virtio_net_common.sh b/tools/testing/selftests/drivers/net/virtio_net/virtio_net_common.sh
new file mode 100644
index 00000000000000..57bd8055e2e58e
--- /dev/null
+++ b/tools/testing/selftests/drivers/net/virtio_net/virtio_net_common.sh
@@ -0,0 +1,99 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+# This assumes running on a host with two virtio interfaces connected
+# back to back. Example script to do such wire-up of tap devices would
+# look like this:
+#
+# =======================================================================================================
+# #!/bin/bash
+#
+# 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
+# =======================================================================================================
+
+REQUIRE_MZ="no"
+NETIF_CREATE="no"
+NETIF_FIND_DRIVER="virtio_net"
+NUM_NETIFS=2
+
+H1_IPV4="192.0.2.1"
+H2_IPV4="192.0.2.2"
+H1_IPV6="2001:db8:1::1"
+H2_IPV6="2001:db8:1::2"
+
+VIRTIO_NET_F_MAC=5
+
+virtio_device_get()
+{
+	local dev=$1; shift
+	local device_path="/sys/class/net/$dev/device/"
+
+	basename `realpath $device_path`
+}
+
+virtio_device_rebind()
+{
+	local dev=$1; shift
+	local device=`virtio_device_get $dev`
+
+	echo "$device" > /sys/bus/virtio/drivers/virtio_net/unbind
+	echo "$device" > /sys/bus/virtio/drivers/virtio_net/bind
+}
+
+virtio_debugfs_get()
+{
+	local dev=$1; shift
+	local device=`virtio_device_get $dev`
+
+	echo /sys/kernel/debug/virtio/$device/
+}
+
+check_virtio_debugfs()
+{
+	local dev=$1; shift
+	local debugfs=`virtio_debugfs_get $dev`
+
+	if [ ! -f "$debugfs/device_features" ] ||
+	   [ ! -f "$debugfs/filter_feature_add"  ] ||
+	   [ ! -f "$debugfs/filter_feature_del"  ] ||
+	   [ ! -f "$debugfs/filter_features"  ] ||
+	   [ ! -f "$debugfs/filter_features_clear"  ]; then
+		echo "SKIP: not possible to access debugfs for $dev"
+		exit $ksft_skip
+	fi
+}
+
+virtio_feature_present()
+{
+	local dev=$1; shift
+	local feature=$1; shift
+	local debugfs=`virtio_debugfs_get $dev`
+
+	cat $debugfs/device_features |grep "^$feature$" &> /dev/null
+	return $?
+}
+
+virtio_filter_features_clear()
+{
+	local dev=$1; shift
+	local debugfs=`virtio_debugfs_get $dev`
+
+	echo "1" > $debugfs/filter_features_clear
+}
+
+virtio_filter_feature_add()
+{
+	local dev=$1; shift
+	local feature=$1; shift
+	local debugfs=`virtio_debugfs_get $dev`
+
+	echo "$feature" > $debugfs/filter_feature_add
+}
diff --git a/tools/testing/selftests/net/forwarding/lib.sh b/tools/testing/selftests/net/forwarding/lib.sh
index 7913c6ee418d5e..3353a17459465f 100644
--- a/tools/testing/selftests/net/forwarding/lib.sh
+++ b/tools/testing/selftests/net/forwarding/lib.sh
@@ -84,6 +84,43 @@ declare -A NETIFS=(
 # e.g. a low-power board.
 : "${KSFT_MACHINE_SLOW:=no}"
 
+##############################################################################
+# Find netifs by test-specified driver name
+
+driver_name_get()
+{
+	local dev=$1; shift
+	local driver_path="/sys/class/net/$dev/device/driver"
+
+	if [[ -L $driver_path ]]; then
+		basename `realpath $driver_path`
+	fi
+}
+
+netif_find_driver()
+{
+	local ifnames=`ip -j link show | jq -r ".[].ifname"`
+	local count=0
+
+	for ifname in $ifnames
+	do
+		local driver_name=`driver_name_get $ifname`
+		if [[ ! -z $driver_name && $driver_name == $NETIF_FIND_DRIVER ]]; then
+			count=$((count + 1))
+			NETIFS[p$count]="$ifname"
+		fi
+	done
+}
+
+# Whether to find netdevice according to the driver speficied by the importer
+: "${NETIF_FIND_DRIVER:=}"
+
+if [[ $NETIF_FIND_DRIVER ]]; then
+	unset NETIFS
+	declare -A NETIFS
+	netif_find_driver
+fi
+
 net_forwarding_dir=$(dirname "$(readlink -e "${BASH_SOURCE[0]}")")
 
 if [[ -f $net_forwarding_dir/forwarding.config ]]; then
@@ -246,6 +283,18 @@ if [[ "$(id -u)" -ne 0 ]]; then
 	exit $ksft_skip
 fi
 
+check_driver()
+{
+	local dev=$1; shift
+	local expected=$1; shift
+	local driver_name=`driver_name_get $dev`
+
+	if [[ $driver_name != $expected ]]; then
+		echo "SKIP: expected driver $expected for $dev, got $driver_name instead"
+		exit $ksft_skip
+	fi
+}
+
 if [[ "$CHECK_TC" = "yes" ]]; then
 	check_tc_version
 fi
@@ -689,6 +738,19 @@ setup_wait()
 	sleep $WAIT_TIME
 }
 
+wait_for_dev()
+{
+        local dev=$1; shift
+        local timeout=${1:-$WAIT_TIMEOUT}; shift
+
+        slowwait $timeout ip link show dev $dev &> /dev/null
+        if (( $? )); then
+                check_err 1
+                log_test wait_for_dev "Interface $dev did not appear."
+                exit $EXIT_STATUS
+        fi
+}
+
 cmd_jq()
 {
 	local cmd=$1