system/qtest: Support comments in input commands

Allow the qtest input to include comment lines, which start with '#'.
This allows writing an input file for qtest which includes commentary,
like this:

  # set up TCR in bank 0
  write 0x1001000e 2 0
  # TCR TXEN
  write 0x10010000 2 1

which can make hand-writing or annotating reproduce cases a bit
more convenient.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20260226175700.1319767-1-peter.maydell@linaro.org

system/qtest.c

@@ -71,6 +71,7 @@ static void *qtest_server_send_opaque;
  *
  * Extra ASCII space characters in command inputs are permitted and ignored.
  * Lines containing only spaces are permitted and ignored.
+ * Lines that start with a '#' character (comments) are permitted and ignored.
  *
  * Valid requests
  * ^^^^^^^^^^^^^^
@@ -370,8 +371,8 @@ static void qtest_process_command(CharFrontend *chr, gchar **words)
         fprintf(qtest_log_fp, "\n");
     }
 
-    if (!command) {
-        /* Input line was blank: ignore it */
+    if (!command || command[0] == '#') {
+        /* Input line was blank or a comment: ignore it */
         return;
     }