qemu-options: Bail out on unsupported options instead of silently ignoring them

The dangling remainder of the -tdf option revealed a deficiency in our
option parsing: Options that have been declared, but are not supported
in the switch-case statement in vl.c and not handled in the OS-specifc
os_parse_cmd_args() functions are currently silently ignored. We should
rather tell the users that they specified something that we can not
handle, so let's print an error message and exit instead.

Reported-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <1525453270-23074-3-git-send-email-thuth@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/qemu-common.h

@@ -137,7 +137,7 @@ char *qemu_find_file(int type, const char *name);
 /* OS specific functions */
 void os_setup_early_signal_handling(void);
 char *os_find_datadir(void);
-void os_parse_cmd_args(int index, const char *optarg);
+int os_parse_cmd_args(int index, const char *optarg);
 
 #include "qemu/module.h"
 

os-posix.c

@@ -165,7 +165,7 @@ static bool os_parse_runas_uid_gid(const char *optarg)
  * Parse OS specific command line options.
  * return 0 if option handled, -1 otherwise
  */
-void os_parse_cmd_args(int index, const char *optarg)
+int os_parse_cmd_args(int index, const char *optarg)
 {
     switch (index) {
 #ifdef CONFIG_SLIRP
@@ -199,7 +199,11 @@ void os_parse_cmd_args(int index, const char *optarg)
         fips_set_state(true);
         break;
 #endif
+    default:
+        return -1;
     }
+
+    return 0;
 }
 
 static void change_process_uid(void)

os-win32.c

@@ -93,9 +93,9 @@ void os_set_line_buffering(void)
  * Parse OS specific command line options.
  * return 0 if option handled, -1 otherwise
  */
-void os_parse_cmd_args(int index, const char *optarg)
+int os_parse_cmd_args(int index, const char *optarg)
 {
-    return;
+    return -1;
 }
 
 int qemu_create_pidfile(const char *filename)

vl.c

@@ -4033,7 +4033,10 @@ int main(int argc, char **argv, char **envp)
                 }
                 break;
             default:
-                os_parse_cmd_args(popt->index, optarg);
+                if (os_parse_cmd_args(popt->index, optarg)) {
+                    error_report("Option not supported in this build");
+                    exit(1);
+                }
             }
         }
     }