shared: cleanup dlopening libjansson depending on configure optionsth/libnm_jansson-2

- assert that WITH_JANSSON and JANSSON_SONAME are defined consistently.
  This check ensures that we can check at compile time that nm_json_vt()
  will always fail (because JANSSON_SONAME) is undefined.
  That is interesting, because this means you can do a compile time
  for !WITH_JANSSON, and know if nm_json_vt() will *never* succeed.
  With that, we could let the linker know when the code is unused
  and remove all uses of nm_json_vt(), without using the traditional
  conditional compilation with "#if WITH_JANSSON". But of course, we
  currently don't do this micro optimization to remove defunct code.

- drop the "mode" helper variable and pass the flags directly to
  dlopen().

2 files changed, 38 insertions, 13 deletions

diff --git a/libnm-core/tests/test-setting.c b/libnm-core/tests/test-setting.c
index 5ec0ccbdb1..1b53baeda3 100644
--- a/libnm-core/tests/test-setting.c
+++ b/libnm-core/tests/test-setting.c
@@ -971,6 +971,24 @@ test_dcb_bandwidth_sums (void)
 /*****************************************************************************/
 
 static void
+test_nm_json (void)
+{
+	g_assert (NM_IN_SET (WITH_JANSSON, 0, 1));
+
+#if WITH_JANSSON
+	g_assert (nm_json_vt ());
+#else
+	g_assert (!nm_json_vt ());
+#endif
+
+#if WITH_JANSSON != defined (JANSSON_SONAME)
+#error "WITH_JANSON and JANSSON_SONAME are defined inconsistently."
+#endif
+}
+
+/*****************************************************************************/
+
+static void
 _test_team_config_sync (const char *team_config,
                         int notify_peer_count,
                         int notify_peers_interval,
@@ -4087,6 +4105,7 @@ main (int argc, char **argv)
 	g_test_add_func ("/libnm/settings/bridge/vlans", test_bridge_vlans);
 	g_test_add_func ("/libnm/settings/bridge/verify", test_bridge_verify);
 
+	g_test_add_func ("/libnm/test_nm_json", test_nm_json);
 	g_test_add_func ("/libnm/settings/team/sync_runner_from_config_roundrobin",
 	                 test_runner_roundrobin_sync_from_config);
 	g_test_add_func ("/libnm/settings/team/sync_runner_from_config_broadcast",
diff --git a/shared/nm-glib-aux/nm-json-aux.c b/shared/nm-glib-aux/nm-json-aux.c
index aba979d205..4758d2a1bd 100644
--- a/shared/nm-glib-aux/nm-json-aux.c
+++ b/shared/nm-glib-aux/nm-json-aux.c
@@ -147,26 +147,32 @@ static NMJsonVtInternal *
 _nm_json_vt_internal_load (void)
 {
 	NMJsonVtInternal *v;
-	void *handle = NULL;
-	int mode;
+	const char *soname;
+	void *handle;
 
 	v = g_new (NMJsonVtInternal, 1);
-
 	*v = (NMJsonVtInternal) { };
 
-#ifndef JANSSON_SONAME
-#define JANSSON_SONAME ""
-#endif
-
-	mode = RTLD_LAZY | RTLD_LOCAL | RTLD_NODELETE | RTLD_DEEPBIND;
-#if defined (ASAN_BUILD)
-	/* Address sanitizer is incompatible with RTLD_DEEPBIND. */
-	mode &= ~RTLD_DEEPBIND;
+#if WITH_JANSSON && defined (JANSSON_SONAME)
+	G_STATIC_ASSERT_EXPR (NM_STRLEN (JANSSON_SONAME) > 0);
+	nm_assert (strlen (JANSSON_SONAME) > 0);
+	soname = JANSSON_SONAME;
+#elif !WITH_JANSSON && !defined (JANSSON_SONAME)
+	soname = NULL;
+#else
+#error "WITH_JANSON and JANSSON_SONAME are defined inconsistently."
 #endif
 
-	if (strlen (JANSSON_SONAME) > 0)
-		handle = dlopen (JANSSON_SONAME, mode);
+	if (!soname)
+		return v;
 
+	handle = dlopen (soname,   RTLD_LAZY
+	                         | RTLD_LOCAL
+	                         | RTLD_NODELETE
+#if !defined (ASAN_BUILD)
+	                         | RTLD_DEEPBIND
+#endif
+	                         | 0);
 	if (!handle)
 		return v;