api wrapper: only reset the current config if this call set it

Instead of *always* resetting the current_config to null, we should only
reset it if this API call set it.

This allows nesting of API calls, e.g. c->checkpoint() can pass stuff into
criu.c, which can call c->init_pid() and not lose the ability to log stuff
afterwards.

Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>

src/lxc/lxccontainer.c

@@ -345,39 +345,71 @@ static bool do_lxcapi_is_defined(struct lxc_container *c)
 static rettype fnname(struct lxc_container *c)				\
 {									\
 	rettype ret;							\
-	current_config = c ? c->lxc_conf : NULL;			\
+	bool reset_config = false;					\
+									\
+	if (!current_config && c && c->lxc_conf) {			\
+		current_config = c->lxc_conf;				\
+		reset_config = true;					\
+	}								\
+									\
 	ret = do_##fnname(c);						\
-	current_config = NULL;						\
+	if (reset_config)						\
+		current_config = NULL;					\
+									\
 	return ret;							\
 }
 
 #define WRAP_API_1(rettype, fnname, t1)					\
 static rettype fnname(struct lxc_container *c, t1 a1)			\
 {									\
 	rettype ret;							\
-	current_config = c ? c->lxc_conf : NULL;			\
+	bool reset_config = false;					\
+									\
+	if (!current_config && c && c->lxc_conf) {			\
+		current_config = c->lxc_conf;				\
+		reset_config = true;					\
+	}								\
+									\
 	ret = do_##fnname(c, a1);					\
-	current_config = NULL;						\
+	if (reset_config)						\
+		current_config = NULL;					\
+									\
 	return ret;							\
 }
 
 #define WRAP_API_2(rettype, fnname, t1, t2)				\
 static rettype fnname(struct lxc_container *c, t1 a1, t2 a2)		\
 {									\
 	rettype ret;							\
-	current_config = c ? c->lxc_conf : NULL;			\
+	bool reset_config = false;					\
+									\
+	if (!current_config && c && c->lxc_conf) {			\
+		current_config = c->lxc_conf;				\
+		reset_config = true;					\
+	}								\
+									\
 	ret = do_##fnname(c, a1, a2);					\
-	current_config = NULL;						\
+	if (reset_config)						\
+		current_config = NULL;					\
+									\
 	return ret;							\
 }
 
 #define WRAP_API_3(rettype, fnname, t1, t2, t3)				\
 static rettype fnname(struct lxc_container *c, t1 a1, t2 a2, t3 a3)	\
 {									\
 	rettype ret;							\
-	current_config = c ? c->lxc_conf : NULL;			\
+	bool reset_config = false;					\
+									\
+	if (!current_config && c && c->lxc_conf) {			\
+		current_config = c->lxc_conf;				\
+		reset_config = true;					\
+	}								\
+									\
 	ret = do_##fnname(c, a1, a2, a3);				\
-	current_config = NULL;						\
+	if (reset_config)						\
+		current_config = NULL;					\
+									\
 	return ret;							\
 }