vtest: add command line option to stop forking

this makes it easier to apitrace this

vtest/vtest_server.c

@@ -137,15 +137,26 @@ fail:
     fprintf(stderr, "socket failed - closing renderer\n");
     vtest_destroy_renderer();
     close(new_fd);
-    exit(0);
+    return 0;
 }
 
-int main(void)
+int main(int argc, char **argv)
 {
     int sock, new_fd, ret;
     pid_t pid;
+    bool do_fork = true;
     struct sigaction sa;
 
+    if (argc > 1) {
+      if (!strcmp(argv[1], "--no-fork"))
+	do_fork = false;
+      else {
+	fprintf(stderr, "illegal command line parameter\n");
+	exit(-1);
+      }
+    }
+
+    if (do_fork) {
       sa.sa_handler = SIG_IGN;
       sigemptyset(&sa.sa_mask);
       sa.sa_flags = 0;
@@ -153,20 +164,27 @@ int main(void)
 	perror(0);
 	exit(1);
       }
+    }
 
     sock = vtest_open_socket("/tmp/.virgl_test");
 restart:
     new_fd = wait_for_socket_accept(sock);
 
+    if (do_fork) {
       /* fork a renderer process */
       switch ((pid = fork())) {
       case 0:
 	run_renderer(new_fd);
+	exit(0);
 	break;
       case -1:
       default:
 	close(new_fd);
 	goto restart;
       }
+    } else {
+      run_renderer(new_fd);
+      goto restart;
+    }
     close(sock);
 }