mxqd: Check prerequisites

mxqd.c

@@ -44,6 +44,7 @@
 
 #include "mxqd_control.h"
 #include "keywordset.h"
+#include "parser.tab.h"
 
 #ifndef MXQ_INITIAL_PATH
 #  define MXQ_INITIAL_PATH      "/sbin:/bin:/usr/sbin:/usr/bin:/usr/local/sbin:/usr/local/bin"
@@ -1421,6 +1422,19 @@ static int server_is_qualified(struct mxq_server *server, struct mxq_group *grou
             return 0;
     }
 
+    if (*group->prerequisites != 0) {
+        struct parser_context parser_context = {
+            .input = group->prerequisites,
+            .tags = server->prerequisites,
+            .pos=0,
+            .result = 0,
+        };
+        if (yyparse(&parser_context))
+            return 0;   // syntax error in expression
+        if (parser_context.result == 0)
+            return 0;   // avaluated to false
+    }
+
     return (1);
 }