hmp: Add flag for preconfig commands

Add a flag to command definitions to allow them to be used in preconfig
and check it.
If users try to use commands that aren't available, tell them to use
the exit_preconfig comand we're adding in a few patches.
Signed-off-by: NDr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: NMarkus Armbruster <armbru@redhat.com>
Reviewed-by: NIgor Mammedov <imammedo@redhat.com>
Message-Id: <20180620153947.30834-2-dgilbert@redhat.com>
Signed-off-by: NDr. David Alan Gilbert <dgilbert@redhat.com>

monitor.c

@@ -128,6 +128,7 @@ typedef struct mon_cmd_t {
     const char *args_type;
     const char *params;
     const char *help;
+    const char *flags; /* p=preconfig */
     void (*cmd)(Monitor *mon, const QDict *qdict);
     /* @sub_table is a list of 2nd level of commands. If it does not exist,
      * cmd should be used. If it exists, sub_table[?].cmd should be
@@ -958,6 +959,19 @@ static int parse_cmdline(const char *cmdline,
     return -1;
 }
 
+/*
+ * Returns true if the command can be executed in preconfig mode
+ * i.e. it has the 'p' flag.
+ */
+static bool cmd_can_preconfig(const mon_cmd_t *cmd)
+{
+    if (!cmd->flags) {
+        return false;
+    }
+
+    return strchr(cmd->flags, 'p');
+}
+
 static void help_cmd_dump_one(Monitor *mon,
                               const mon_cmd_t *cmd,
                               char **prefix_args,
@@ -3041,6 +3055,12 @@ static const mon_cmd_t *monitor_parse_command(Monitor *mon,
                        (int)(p - cmdp_start), cmdp_start);
         return NULL;
     }
+    if (runstate_check(RUN_STATE_PRECONFIG) && !cmd_can_preconfig(cmd)) {
+        monitor_printf(mon, "Command '%.*s' not available with -preconfig "
+                            "until after exit_preconfig.\n",
+                       (int)(p - cmdp_start), cmdp_start);
+        return NULL;
+    }
 
     /* filter out following useless space */
     while (qemu_isspace(*p)) {