uwrap: Add library constructor and move pthread_atfork inside.

Library constructor is used for pthread_atfork call. Moved here because
pthread_atfork is cumulative and should be called only once.

Signed-off-by: Robin Hack <hack.robin@gmail.com>
Reviewed-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>

2 files changed, 39 insertions, 9 deletions

diff --git a/lib/uid_wrapper/uid_wrapper.c b/lib/uid_wrapper/uid_wrapper.c
index a492b965d5..a955e77f0e 100644
--- a/lib/uid_wrapper/uid_wrapper.c
+++ b/lib/uid_wrapper/uid_wrapper.c
@@ -51,6 +51,12 @@
 	pthread_mutex_unlock(&( m ## _mutex)); \
 } while(0)
 
+#ifdef HAVE_CONSTRUCTOR_ATTRIBUTE
+#define CONSTRUCTOR_ATTRIBUTE __attribute__ ((constructor))
+#else
+#define CONSTRUCTOR_ATTRIBUTE
+#endif /* HAVE_CONSTRUCTOR_ATTRIBUTE */
+
 #ifdef HAVE_DESTRUCTOR_ATTRIBUTE
 #define DESTRUCTOR_ATTRIBUTE __attribute__ ((destructor))
 #else
@@ -249,6 +255,7 @@ static pthread_mutex_t uwrap_id_mutex = PTHREAD_MUTEX_INITIALIZER;
  *********************************************************/
 
 bool uid_wrapper_enabled(void);
+void uwrap_constructor(void) CONSTRUCTOR_ATTRIBUTE;
 void uwrap_destructor(void) DESTRUCTOR_ATTRIBUTE;
 
 /*********************************************************
@@ -591,15 +598,6 @@ static void uwrap_init(void)
 
 	UWRAP_LOG(UWRAP_LOG_DEBUG, "Initialize uid_wrapper");
 
-	/*
-	 * If we hold a lock and the application forks, then the child
-	 * is not able to unlock the mutex and we are in a deadlock.
-	 * This should prevent such deadlocks.
-	 */
-	pthread_atfork(&uwrap_thread_prepare,
-		       &uwrap_thread_parent,
-		       &uwrap_thread_child);
-
 	UWRAP_LOCK(uwrap_id);
 
 	uwrap.initialised = true;
@@ -1249,6 +1247,21 @@ long int syscall (long int sysno, ...)
 #endif /* HAVE_SYS_SYSCALL_H || HAVE_SYSCALL_H */
 
 /****************************
+ * CONSTRUCTOR
+ ***************************/
+void uwrap_constructor(void)
+{
+	/*
+	* If we hold a lock and the application forks, then the child
+	* is not able to unlock the mutex and we are in a deadlock.
+	* This should prevent such deadlocks.
+	*/
+	pthread_atfork(&uwrap_thread_prepare,
+		       &uwrap_thread_parent,
+		       &uwrap_thread_child);
+}
+
+/****************************
  * DESTRUCTOR
  ***************************/
 
diff --git a/lib/uid_wrapper/wscript b/lib/uid_wrapper/wscript
index 6b585956e0..bd797e5a72 100644
--- a/lib/uid_wrapper/wscript
+++ b/lib/uid_wrapper/wscript
@@ -21,6 +21,23 @@ def configure(conf):
             addmain=False,
             msg='Checking for thread local storage')
 
+        # check HAVE_CONSTRUCTOR_ATTRIBUTE
+        conf.CHECK_CODE('''
+            void test_constructor_attribute(void) __attribute__ ((constructor));
+
+            void test_constructor_attribute(void)
+            {
+                return;
+            }
+
+            int main(void) {
+                return 0;
+            }
+            ''',
+            'HAVE_CONSTRUCTOR_ATTRIBUTE',
+            addmain=False,
+            msg='Checking for library constructor support')
+
         # check HAVE_DESTRUCTOR_ATTRIBUTE
         conf.CHECK_CODE('''
             void test_destructor_attribute(void) __attribute__ ((destructor));