monitor: Create MonitorHMP with readline state

The ReadLineState in Monitor is only used for HMP monitors. Create
MonitorHMP and move it there.

Can't use container_of() in hmp_change().  Cast instead, and mark
FIXME.  Will be cleaned up shortly.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20190613153405.24769-5-kwolf@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[Superfluous variable in monitor_data_destroy() eliminated, whitespace
tweaked in hmp_change(), commit message improved]
Signed-off-by: Markus Armbruster <armbru@redhat.com>

hmp.c

@@ -1943,6 +1943,8 @@ static void hmp_change_read_arg(void *opaque, const char *password,
 
 void hmp_change(Monitor *mon, const QDict *qdict)
 {
+    /* FIXME Make MonitorHMP public and use container_of */
+    MonitorHMP *hmp_mon = (MonitorHMP *)mon;
     const char *device = qdict_get_str(qdict, "device");
     const char *target = qdict_get_str(qdict, "target");
     const char *arg = qdict_get_try_str(qdict, "arg");
@@ -1960,7 +1962,7 @@ void hmp_change(Monitor *mon, const QDict *qdict)
         if (strcmp(target, "passwd") == 0 ||
             strcmp(target, "password") == 0) {
             if (!arg) {
-                monitor_read_password(mon, hmp_change_read_arg, NULL);
+                monitor_read_password(hmp_mon, hmp_change_read_arg, NULL);
                 return;
             }
         }

include/monitor/monitor.h

@@ -6,6 +6,7 @@
 #include "qemu/readline.h"
 
 extern __thread Monitor *cur_mon;
+typedef struct MonitorHMP MonitorHMP;
 
 /* flags for monitor_init */
 /* 0x01 unused */
@@ -34,8 +35,8 @@ void monitor_flush(Monitor *mon);
 int monitor_set_cpu(int cpu_index);
 int monitor_get_cpu_index(void);
 
-void monitor_read_command(Monitor *mon, int show_prompt);
-int monitor_read_password(Monitor *mon, ReadLineFunc *readline_func,
+void monitor_read_command(MonitorHMP *mon, int show_prompt);
+int monitor_read_password(MonitorHMP *mon, ReadLineFunc *readline_func,
                           void *opaque);
 
 AddfdInfo *monitor_fdset_add_fd(int fd, bool has_fdset_id, int64_t fdset_id,