selftests/net: Improve bind_bhash.sh to accommodate predictable network interface names

Starting with v197, systemd uses predictable interface network names,
the traditional interface naming scheme (eth0) is deprecated, therefore
it cannot be assumed that the eth0 interface exists on the host.

This modification makes the bind_bhash test program run in a separate
network namespace and no longer needs to consider the name of the
network interface on the host.

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

tools/testing/selftests/net/bind_bhash.sh

···
 # SPDX-License-Identifier: GPL-2.0
 
 NR_FILES=32768
-SAVED_NR_FILES=$(ulimit -n)
+readonly NETNS="ns-$(mktemp -u XXXXXX)"
 
 # default values
 port=443
···
 done
 
 setup() {
+    ip netns add "${NETNS}"
+    ip -netns "${NETNS}" link add veth0 type veth peer name veth1
+    ip -netns "${NETNS}" link set lo up
+    ip -netns "${NETNS}" link set veth0 up
+    ip -netns "${NETNS}" link set veth1 up
+
     if [[ "$use_v6" == true ]]; then
-	ip addr add $addr_v6 nodad dev eth0
+        ip -netns "${NETNS}" addr add $addr_v6 nodad dev veth0
     else
-	ip addr add $addr_v4 dev lo
+        ip -netns "${NETNS}" addr add $addr_v4 dev lo
     fi
-	ulimit -n $NR_FILES
 }
 
 cleanup() {
-    if [[ "$use_v6" == true ]]; then
-	ip addr del $addr_v6 dev eth0
-    else
-	ip addr del $addr_v4/32 dev lo
-    fi
-    ulimit -n $SAVED_NR_FILES
+    ip netns del "${NETNS}"
 }
 
 if [[ "$addr" != "" ]]; then
···
 fi
 setup
 if [[ "$use_v6" == true ]] ; then
-    ./bind_bhash $port "ipv6" $addr_v6
+    ip netns exec "${NETNS}" sh -c \
+        "ulimit -n ${NR_FILES};./bind_bhash ${port} ipv6 ${addr_v6}"
 else
-    ./bind_bhash $port "ipv4" $addr_v4
+    ip netns exec "${NETNS}" sh -c \
+        "ulimit -n ${NR_FILES};./bind_bhash ${port} ipv4 ${addr_v4}"
 fi
 cleanup