selftests: net: lib: avoid error removing empty netns name

If there is an error to create the first netns with 'setup_ns()',
'cleanup_ns()' will be called with an empty string as first parameter.

The consequences is that 'cleanup_ns()' will try to delete an invalid
netns, and wait 20 seconds if the netns list is empty.

Instead of just checking if the name is not empty, convert the string
separated by spaces to an array. Manipulating the array is cleaner, and
calling 'cleanup_ns()' with an empty array will be a no-op.

Fixes: 25ae948 ("selftests/net: add lib.sh")
Cc: stable@vger.kernel.org
Acked-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Hangbin Liu <liuhangbin@gmail.com>
Link: https://lore.kernel.org/r/20240605-upstream-net-20240605-selftests-net-lib-fixes-v1-2-b3afadd368c9@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: matttbe

tools/testing/selftests/net/lib.sh

@@ -15,7 +15,7 @@ ksft_xfail=2
 ksft_skip=4
 
 # namespace list created by setup_ns
-NS_LIST=""
+NS_LIST=()
 
 ##############################################################################
 # Helpers
@@ -137,6 +137,7 @@ cleanup_ns()
 	fi
 
 	for ns in "$@"; do
+		[ -z "${ns}" ] && continue
 		ip netns delete "${ns}" &> /dev/null
 		if ! busywait $BUSYWAIT_TIMEOUT ip netns list \| grep -vq "^$ns$" &> /dev/null; then
 			echo "Warn: Failed to remove namespace $ns"
@@ -150,7 +151,7 @@ cleanup_ns()
 
 cleanup_all_ns()
 {
-	cleanup_ns $NS_LIST
+	cleanup_ns "${NS_LIST[@]}"
 }
 
 # setup netns with given names as prefix. e.g
@@ -159,7 +160,7 @@ setup_ns()
 {
 	local ns=""
 	local ns_name=""
-	local ns_list=""
+	local ns_list=()
 	local ns_exist=
 	for ns_name in "$@"; do
 		# Some test may setup/remove same netns multi times
@@ -175,13 +176,13 @@ setup_ns()
 
 		if ! ip netns add "$ns"; then
 			echo "Failed to create namespace $ns_name"
-			cleanup_ns "$ns_list"
+			cleanup_ns "${ns_list[@]}"
 			return $ksft_skip
 		fi
 		ip -n "$ns" link set lo up
-		! $ns_exist && ns_list="$ns_list $ns"
+		! $ns_exist && ns_list+=("$ns")
 	done
-	NS_LIST="$NS_LIST $ns_list"
+	NS_LIST+=("${ns_list[@]}")
 }
 
 tc_rule_stats_get()