[v4,06/22] monitor: introduce HumanReadableText and HMP support

diff --git a/include/monitor/hmp.h b/include/monitor/hmp.h
index a2cb002a3a..96d014826a 100644
--- a/include/monitor/hmp.h
+++ b/include/monitor/hmp.h
@@ -15,6 +15,7 @@ 
 #define HMP_H
 
 #include "qemu/readline.h"
+#include "qapi/qapi-types-common.h"
 
 bool hmp_handle_error(Monitor *mon, Error *err);
 
@@ -130,5 +131,7 @@  void hmp_replay_delete_break(Monitor *mon, const QDict *qdict);
 void hmp_replay_seek(Monitor *mon, const QDict *qdict);
 void hmp_info_dirty_rate(Monitor *mon, const QDict *qdict);
 void hmp_calc_dirty_rate(Monitor *mon, const QDict *qdict);
+void hmp_human_readable_text_helper(Monitor *mon,
+                                    HumanReadableText *(*qmp_handler)(Error **));
 
 #endif
diff --git a/include/monitor/monitor.h b/include/monitor/monitor.h
index 1a8a369b50..12d395d62d 100644
--- a/include/monitor/monitor.h
+++ b/include/monitor/monitor.h
@@ -53,5 +53,7 @@  int64_t monitor_fdset_dup_fd_find(int dup_fd);
 
 void monitor_register_hmp(const char *name, bool info,
                           void (*cmd)(Monitor *mon, const QDict *qdict));
+void monitor_register_hmp_info_hrt(const char *name,
+                                   HumanReadableText *(*handler)(Error **errp));
 
 #endif /* MONITOR_H */
diff --git a/include/qapi/type-helpers.h b/include/qapi/type-helpers.h
new file mode 100644
index 0000000000..be1f181526
--- /dev/null
+++ b/include/qapi/type-helpers.h
@@ -0,0 +1,14 @@ 
+/*
+ * QAPI common helper functions
+ *
+ * This file provides helper functions related to types defined
+ * in the QAPI schema.
+ *
+ * This work is licensed under the terms of the GNU LGPL, version 2.1 or later.
+ * See the COPYING.LIB file in the top-level directory.
+ *
+ */
+
+#include "qapi/qapi-types-common.h"
+
+HumanReadableText *human_readable_text_from_str(GString *str);
diff --git a/monitor/hmp.c b/monitor/hmp.c
index d50c3124e1..352a4d9c80 100644
--- a/monitor/hmp.c
+++ b/monitor/hmp.c
@@ -1061,6 +1061,31 @@  fail:
     return NULL;
 }
 
+static void hmp_info_human_readable_text(Monitor *mon,
+                                         HumanReadableText *(*handler)(Error **))
+{
+    Error *err = NULL;
+    g_autoptr(HumanReadableText) info = handler(&err);
+
+    if (hmp_handle_error(mon, err)) {
+        return;
+    }
+
+    monitor_printf(mon, "%s", info->human_readable_text);
+}
+
+static void handle_hmp_command_exec(Monitor *mon,
+                                    const HMPCommand *cmd,
+                                    QDict *qdict)
+{
+    if (cmd->cmd_info_hrt) {
+        hmp_info_human_readable_text(mon,
+                                     cmd->cmd_info_hrt);
+    } else {
+        cmd->cmd(mon, qdict);
+    }
+}
+
 typedef struct HandleHmpCommandCo {
     Monitor *mon;
     const HMPCommand *cmd;
@@ -1071,7 +1096,7 @@  typedef struct HandleHmpCommandCo {
 static void handle_hmp_command_co(void *opaque)
 {
     HandleHmpCommandCo *data = opaque;
-    data->cmd->cmd(data->mon, data->qdict);
+    handle_hmp_command_exec(data->mon, data->cmd, data->qdict);
     monitor_set_cur(qemu_coroutine_self(), NULL);
     data->done = true;
 }
@@ -1089,7 +1114,7 @@  void handle_hmp_command(MonitorHMP *mon, const char *cmdline)
         return;
     }
 
-    if (!cmd->cmd) {
+    if (!cmd->cmd && !cmd->cmd_info_hrt) {
         /* FIXME: is it useful to try autoload modules here ??? */
         monitor_printf(&mon->common, "Command \"%.*s\" is not available.\n",
                        (int)(cmdline - cmd_start), cmd_start);
@@ -1109,7 +1134,7 @@  void handle_hmp_command(MonitorHMP *mon, const char *cmdline)
     if (!cmd->coroutine) {
         /* old_mon is non-NULL when called from qmp_human_monitor_command() */
         Monitor *old_mon = monitor_set_cur(qemu_coroutine_self(), &mon->common);
-        cmd->cmd(&mon->common, qdict);
+        handle_hmp_command_exec(&mon->common, cmd, qdict);
         monitor_set_cur(qemu_coroutine_self(), old_mon);
     } else {
         HandleHmpCommandCo data = {
diff --git a/monitor/misc.c b/monitor/misc.c
index ffe7966870..3cb5269356 100644
--- a/monitor/misc.c
+++ b/monitor/misc.c
@@ -1963,7 +1963,7 @@  void monitor_register_hmp(const char *name, bool info,
 
     while (table->name != NULL) {
         if (strcmp(table->name, name) == 0) {
-            g_assert(table->cmd == NULL);
+            g_assert(table->cmd == NULL && table->cmd_info_hrt == NULL);
             table->cmd = cmd;
             return;
         }
@@ -1972,6 +1972,22 @@  void monitor_register_hmp(const char *name, bool info,
     g_assert_not_reached();
 }
 
+void monitor_register_hmp_info_hrt(const char *name,
+                                   HumanReadableText *(*handler)(Error **errp))
+{
+    HMPCommand *table = hmp_info_cmds;
+
+    while (table->name != NULL) {
+        if (strcmp(table->name, name) == 0) {
+            g_assert(table->cmd == NULL && table->cmd_info_hrt == NULL);
+            table->cmd_info_hrt = handler;
+            return;
+        }
+        table++;
+    }
+    g_assert_not_reached();
+}
+
 void monitor_init_globals(void)
 {
     monitor_init_globals_core();
diff --git a/monitor/monitor-internal.h b/monitor/monitor-internal.h
index 9c3a09cb01..3da3f86c6a 100644
--- a/monitor/monitor-internal.h
+++ b/monitor/monitor-internal.h
@@ -74,6 +74,13 @@  typedef struct HMPCommand {
     const char *help;
     const char *flags; /* p=preconfig */
     void (*cmd)(Monitor *mon, const QDict *qdict);
+    /*
+     * If implementing a command that takes no arguments and simply
+     * prints formatted data, then leave @cmd NULL, and then set
+     * @cmd_info_hrt to the corresponding QMP handler that returns
+     * the formatted text.
+     */
+    HumanReadableText *(*cmd_info_hrt)(Error **errp);
     bool coroutine;
     /*
      * @sub_table is a list of 2nd level of commands. If it does not exist,
diff --git a/qapi/common.json b/qapi/common.json
index 7c976296f0..412cc4f5ae 100644
--- a/qapi/common.json
+++ b/qapi/common.json
@@ -197,3 +197,14 @@ 
 { 'enum': 'GrabToggleKeys',
   'data': [ 'ctrl-ctrl', 'alt-alt', 'shift-shift','meta-meta', 'scrolllock',
             'ctrl-scrolllock' ] }
+
+##
+# @HumanReadableText:
+#
+# @human-readable-text: Formatted output intended for humans.
+#
+# Since: 6.2
+#
+##
+{ 'struct': 'HumanReadableText',
+  'data': { 'human-readable-text': 'str' } }
diff --git a/qapi/meson.build b/qapi/meson.build
index c356a385e3..c0c49c15e4 100644
--- a/qapi/meson.build
+++ b/qapi/meson.build
@@ -10,6 +10,9 @@  util_ss.add(files(
   'string-input-visitor.c',
   'string-output-visitor.c',
 ))
+if have_system
+  util_ss.add(files('qapi-type-helpers.c'))
+endif
 if have_system or have_tools
   util_ss.add(files(
     'qmp-dispatch.c',
diff --git a/qapi/qapi-type-helpers.c b/qapi/qapi-type-helpers.c
new file mode 100644
index 0000000000..f76b34f647
--- /dev/null
+++ b/qapi/qapi-type-helpers.c
@@ -0,0 +1,23 @@ 
+/*
+ * QAPI common helper functions
+ *
+ * This file provides helper functions related to types defined
+ * in the QAPI schema.
+ *
+ * This work is licensed under the terms of the GNU LGPL, version 2.1 or later.
+ * See the COPYING.LIB file in the top-level directory.
+ *
+ */
+
+#include "qemu/osdep.h"
+#include "qapi/error.h"
+#include "qapi/type-helpers.h"
+
+HumanReadableText *human_readable_text_from_str(GString *str)
+{
+    HumanReadableText *ret = g_new0(HumanReadableText, 1);
+
+    ret->human_readable_text = g_steal_pointer(&str->str);
+
+    return ret;
+}