hmp: Update current monitor only in handle_hmp_command()

The current monitor is updated relatively early in the command handling
code even though only the command handler actually needs it.

The current monitor will become coroutine-local later, so we can only
update it when we know in which coroutine the command will be exectued.
Move it to handle_hmp_command() where this information will be
available.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20201005155855.256490-5-kwolf@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

monitor/hmp.c

@@ -1061,6 +1061,7 @@ void handle_hmp_command(MonitorHMP *mon, const char *cmdline)
     QDict *qdict;
     const HMPCommand *cmd;
     const char *cmd_start = cmdline;
+    Monitor *old_mon;
 
     trace_handle_hmp_command(mon, cmdline);
 
@@ -1079,7 +1080,11 @@ void handle_hmp_command(MonitorHMP *mon, const char *cmdline)
         return;
     }
 
+    /* old_mon is non-NULL when called from qmp_human_monitor_command() */
+    old_mon = monitor_set_cur(&mon->common);
     cmd->cmd(&mon->common, qdict);
+    monitor_set_cur(old_mon);
+
     qobject_unref(qdict);
 }
 
@@ -1301,11 +1306,8 @@ static void monitor_find_completion(void *opaque,
 static void monitor_read(void *opaque, const uint8_t *buf, int size)
 {
     MonitorHMP *mon = container_of(opaque, MonitorHMP, common);
-    Monitor *old_mon;
     int i;
 
-    old_mon = monitor_set_cur(&mon->common);
-
     if (mon->rs) {
         for (i = 0; i < size; i++) {
             readline_handle_byte(mon->rs, buf[i]);
@@ -1317,8 +1319,6 @@ static void monitor_read(void *opaque, const uint8_t *buf, int size)
             handle_hmp_command(mon, (char *)buf);
         }
     }
-
-    monitor_set_cur(old_mon);
 }
 
 static void monitor_event(void *opaque, QEMUChrEvent event)

monitor/misc.c

@@ -120,25 +120,20 @@ char *qmp_human_monitor_command(const char *command_line, bool has_cpu_index,
                                 int64_t cpu_index, Error **errp)
 {
     char *output = NULL;
-    Monitor *old_mon;
     MonitorHMP hmp = {};
 
     monitor_data_init(&hmp.common, false, true, false);
 
-    old_mon = monitor_set_cur(&hmp.common);
-
     if (has_cpu_index) {
         int ret = monitor_set_cpu(&hmp.common, cpu_index);
         if (ret < 0) {
-            monitor_set_cur(old_mon);
             error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "cpu-index",
                        "a CPU number");
             goto out;
         }
     }
 
     handle_hmp_command(&hmp, command_line);
-    monitor_set_cur(old_mon);
 
     WITH_QEMU_LOCK_GUARD(&hmp.common.mon_lock) {
         if (qstring_get_length(hmp.common.outbuf) > 0) {