selftests: mptcp: add mptcp_lib_check_output helper

Extract the main part of check() in pm_netlink.sh into a new helper
named mptcp_lib_check_output in mptcp_lib.sh.

This helper will be used for userspace dump addresses tests.
Co-developed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/net/mptcp/mptcp_lib.sh

@@ -319,3 +319,26 @@ mptcp_lib_wait_local_port_listen() {
 		sleep 0.1
 	done
 }
+
+mptcp_lib_check_output() {
+	local err="${1}"
+	local cmd="${2}"
+	local expected="${3}"
+	local cmd_ret=0
+	local out
+
+	if ! out=$(${cmd} 2>"${err}"); then
+		cmd_ret=${?}
+	fi
+
+	if [ ${cmd_ret} -ne 0 ]; then
+		mptcp_lib_print_err "[FAIL] command execution '${cmd}' stderr"
+		cat "${err}"
+		return 2
+	elif [ "${out}" = "${expected}" ]; then
+		return 0
+	else
+		mptcp_lib_print_err "[FAIL] expected '${expected}' got '${out}'"
+		return 1
+	fi
+}

tools/testing/selftests/net/mptcp/pm_netlink.sh

@@ -54,21 +54,17 @@ check()
 	local cmd="$1"
 	local expected="$2"
 	local msg="$3"
-	local out=`$cmd 2>$err`
-	local cmd_ret=$?
+	local rc=0
 
 	printf "%-50s" "$msg"
-	if [ $cmd_ret -ne 0 ]; then
-		echo "[FAIL] command execution '$cmd' stderr "
-		cat $err
-		mptcp_lib_result_fail "${msg} # error ${cmd_ret}"
+	mptcp_lib_check_output "${err}" "${cmd}" "${expected}" || rc=${?}
+	if [ ${rc} -eq 2 ]; then
+		mptcp_lib_result_fail "${msg} # error ${rc}"
 		ret=1
-	elif [ "$out" = "$expected" ]; then
-		echo "[ OK ]"
+	elif [ ${rc} -eq 0 ]; then
+		mptcp_lib_print_ok "[ OK ]"
 		mptcp_lib_result_pass "${msg}"
-	else
-		echo -n "[FAIL] "
-		echo "expected '$expected' got '$out'"
+	elif [ ${rc} -eq 1 ]; then
 		mptcp_lib_result_fail "${msg} # different output"
 		ret=1
 	fi