Same behaviour as in the original patch:

  --with-unitdir	auto-detects the systemd unit path.
  --with-unitdir=PATH	uses the PATH

no --with-unitdir does not install the systemd unit path.

INSTALL description looks fine for what this does.

While at this, extend tests/build/ to cover for this new option.

Fixes: c4b17cf830510 ("tools: add a systemd unit for static rulesets")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
 configure.ac             | 29 +++++++++++++++++++++--------
 tests/build/run-tests.sh |  2 +-
 2 files changed, 22 insertions(+), 9 deletions(-)

diff --git a/configure.ac b/configure.ac
index 42708c9f2470..3a751cb054b9 100644
--- a/configure.ac
+++ b/configure.ac
@@ -115,15 +115,22 @@ AC_CHECK_DECLS([getprotobyname_r, getprotobynumber_r, getservbyport_r], [], [],
 ]])
 
 AC_ARG_WITH([unitdir],
-	[AS_HELP_STRING([--with-unitdir=PATH], [Path to systemd service unit directory])],
-	[unitdir="$withval"],
+	[AS_HELP_STRING([--with-unitdir[=PATH]],
+	[Path to systemd service unit directory, or omit PATH to auto-detect])],
 	[
-		unitdir=$("$PKG_CONFIG" systemd --variable systemdsystemunitdir 2>/dev/null)
-		AS_IF([test -z "$unitdir"], [unitdir='${prefix}/lib/systemd/system'])
-	])
+		if test "x$withval" = "xyes"; then
+			unitdir=$($PKG_CONFIG --variable=systemdsystemunitdir systemd 2>/dev/null)
+			AS_IF([test -z "$unitdir"], [unitdir='${prefix}/lib/systemd/system'])
+		elif test "x$withval" = "xno"; then
+			unitdir=""
+		else
+			unitdir="$withval"
+		fi
+	],
+	[unitdir=""]
+)
 AC_SUBST([unitdir])
 
-
 AC_CONFIG_FILES([					\
 		Makefile				\
 		libnftables.pc				\
@@ -137,5 +144,11 @@ nft configuration:
   use mini-gmp:			${with_mini_gmp}
   enable man page:              ${enable_man_doc}
   libxtables support:		${with_xtables}
-  json output support:          ${with_json}
-  systemd unit:			${unitdir}"
+  json output support:          ${with_json}"
+
+if test "x$unitdir" != "x"; then
+AC_SUBST([unitdir])
+echo "  systemd unit:                 ${unitdir}"
+else
+echo "  systemd unit:                 no"
+fi
diff --git a/tests/build/run-tests.sh b/tests/build/run-tests.sh
index 916df2e2fa8e..1d32d5d8afcb 100755
--- a/tests/build/run-tests.sh
+++ b/tests/build/run-tests.sh
@@ -3,7 +3,7 @@
 log_file="$(pwd)/tests.log"
 dir=../..
 argument=( --without-cli --with-cli=linenoise --with-cli=editline --enable-debug --with-mini-gmp
-	   --enable-man-doc --with-xtables --with-json)
+	   --enable-man-doc --with-xtables --with-json --with-unitdir --with-unidir=/lib/systemd/system)
 ok=0
 failed=0
 
-- 
2.30.2