Add sentinel attribute for NULL terminated arg lists

* src/internal.h (ATTRIBUTE_SENTINEL): New, it's a ggc feature and
  protected as such
* src/util/buf.c (virBufferStrcat): Use it.
* src/util/ebtables.c (ebtablesAddRemoveRule): Use it.
* src/util/iptables.c (iptableAddRemoveRule: Use it.
* src/util/qparams.h (new_qparam_set, append_qparams): Use it.
* docs/apibuild.py: avoid breaking the API generator with that new
  internal keyword macro

docs/apibuild.py

@@ -26,6 +26,7 @@ included_files = {
 
 ignored_words = {
   "ATTRIBUTE_UNUSED": (0, "macro keyword"),
+  "ATTRIBUTE_SENTINEL": (0, "macro keyword"),
   "VIR_DEPRECATED": (0, "macro keyword"),
   "WINAPI": (0, "Windows keyword"),
   "__declspec": (3, "Windows keyword"),

src/internal.h

@@ -92,6 +92,17 @@
 #define ATTRIBUTE_UNUSED __attribute__((__unused__))
 #endif
 
+/**
+ * ATTRIBUTE_SENTINEL:
+ *
+ * Macro to check for NULL-terminated varargs lists
+ */
+#ifndef ATTRIBUTE_SENTINEL
+#if __GNUC_PREREQ (4, 0)
+#define ATTRIBUTE_SENTINEL __attribute__((__sentinel__))
+#endif
+#endif
+
 /**
  * ATTRIBUTE_FMT_PRINTF
  *

src/util/buf.h

@@ -41,7 +41,8 @@ void virBufferAdd(const virBufferPtr buf, const char *str, int len);
 void virBufferAddChar(const virBufferPtr buf, char c);
 void virBufferVSprintf(const virBufferPtr buf, const char *format, ...)
   ATTRIBUTE_FMT_PRINTF(2, 3);
-void virBufferStrcat(const virBufferPtr buf, ...);
+void virBufferStrcat(const virBufferPtr buf, ...)
+  ATTRIBUTE_SENTINEL;
 void virBufferEscapeString(const virBufferPtr buf, const char *format, const char *str);
 void virBufferURIEncodeString (const virBufferPtr buf, const char *str);
 

src/util/ebtables.c

@@ -175,7 +175,7 @@ ebtRulesNew(const char *table,
     return NULL;
 }
 
-static int
+static int ATTRIBUTE_SENTINEL
 ebtablesAddRemoveRule(ebtRules *rules, int action, const char *arg, ...)
 {
     va_list args;

src/util/iptables.c

@@ -382,7 +382,7 @@ iptRulesNew(const char *table,
     return NULL;
 }
 
-static int
+static int ATTRIBUTE_SENTINEL
 iptablesAddRemoveRule(iptRules *rules, int action, const char *arg, ...)
 {
     va_list args;

src/util/qparams.h

@@ -38,10 +38,12 @@ struct qparam_set {
 };
 
 /* New parameter set. */
-extern struct qparam_set *new_qparam_set (int init_alloc, ...);
+extern struct qparam_set *new_qparam_set (int init_alloc, ...)
+    ATTRIBUTE_SENTINEL;
 
 /* Appending parameters. */
-extern int append_qparams (struct qparam_set *ps, ...);
+extern int append_qparams (struct qparam_set *ps, ...)
+    ATTRIBUTE_SENTINEL;
 extern int append_qparam (struct qparam_set *ps,
                           const char *name, const char *value);