monitor: introduce HumanReadableText and HMP support

This provides a foundation on which to convert simple HMP commands to
use QMP. The QMP implementation will generate formatted text targeted
for human consumption, returning it in the HumanReadableText data type.

The HMP command handler will simply print out the formatted string
within the HumanReadableText data type. Since this will be an entirely
formulaic action in the case of HMP commands taking no arguments, a
custom command handler is provided.

Thus instead of registering a 'cmd' callback for the HMP command, a
'cmd_info_hrt' callback is provided, which will simply be a pointer
to the QMP implementation.

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

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

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 */

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);

monitor/hmp.c

@@ -26,6 +26,7 @@
 #include <dirent.h>
 #include "hw/qdev-core.h"
 #include "monitor-internal.h"
+#include "monitor/hmp.h"
 #include "qapi/error.h"
 #include "qapi/qmp/qdict.h"
 #include "qapi/qmp/qnum.h"
@@ -1061,6 +1062,31 @@ 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 +1097,7 @@ 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 +1115,7 @@ 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 +1135,7 @@ 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 = {

monitor/misc.c

@@ -1964,7 +1964,7 @@ 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;
         }
@@ -1973,6 +1973,22 @@ 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();

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,

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' } }

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',

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;
+}