selftests: net: use netdevsim in netns test

Netdevsim has extra register_netdevice_notifier_dev_net notifiers,
use netdevim instead of dummy device to test them out.

Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20250401163452.622454-9-sdf@fomichev.me
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/net/lib.sh

@@ -222,6 +222,31 @@ setup_ns()
 	NS_LIST+=("${ns_list[@]}")
 }
 
+# Create netdevsim with given id and net namespace.
+create_netdevsim() {
+    local id="$1"
+    local ns="$2"
+
+    modprobe netdevsim &> /dev/null
+    udevadm settle
+
+    echo "$id 1" | ip netns exec $ns tee /sys/bus/netdevsim/new_device >/dev/null
+    local dev=$(ip netns exec $ns ls /sys/bus/netdevsim/devices/netdevsim$id/net)
+    ip -netns $ns link set dev $dev name nsim$id
+    ip -netns $ns link set dev nsim$id up
+
+    echo nsim$id
+}
+
+# Remove netdevsim with given id.
+cleanup_netdevsim() {
+    local id="$1"
+
+    if [ -d "/sys/bus/netdevsim/devices/netdevsim$id/net" ]; then
+        echo "$id" > /sys/bus/netdevsim/del_device
+    fi
+}
+
 tc_rule_stats_get()
 {
 	local dev=$1; shift

tools/testing/selftests/net/netns-name.sh

@@ -7,10 +7,12 @@ set -o pipefail
 DEV=dummy-dev0
 DEV2=dummy-dev1
 ALT_NAME=some-alt-name
+NSIM_ADDR=2025
 
 RET_CODE=0
 
 cleanup() {
+    cleanup_netdevsim $NSIM_ADDR
     cleanup_ns $NS $test_ns
 }
 
@@ -25,12 +27,15 @@ setup_ns NS test_ns
 
 #
 # Test basic move without a rename
+# Use netdevsim because it has extra asserts for notifiers.
 #
-ip -netns $NS link add name $DEV type dummy || fail
-ip -netns $NS link set dev $DEV netns $test_ns ||
+
+nsim=$(create_netdevsim $NSIM_ADDR $NS)
+ip -netns $NS link set dev $nsim netns $test_ns ||
     fail "Can't perform a netns move"
-ip -netns $test_ns link show dev $DEV >> /dev/null || fail "Device not found after move"
-ip -netns $test_ns link del $DEV || fail
+ip -netns $test_ns link show dev $nsim >> /dev/null ||
+    fail "Device not found after move"
+cleanup_netdevsim $NSIM_ADDR
 
 #
 # Test move with a conflict