[Qemu-devel] [PATCH v2] qom: Implement qom-get HMP command

["Dr. David Alan Gilbert (git)" <dgilbert@redhat.com>]

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>

This started off as Andreas Färber's implementation from
March 2015, but after feedback from Paolo morphed into
using the json output which handles structs reasonably.

Use with qom-list to find the members of an object.

(qemu) qom-get /backend/console[0]/device/vga.rom[0] size
65536
(qemu) qom-get /machine smm
"auto"
(qemu) qom-get /machine rtc-time
{
    "tm_year": 116,
    "tm_sec": 0,
    "tm_hour": 9,
    "tm_min": 46,
    "tm_mon": 8,
    "tm_mday": 6
}
(qemu) qom-get /machine frob
Property '.frob' not found

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

--
v2
  switched from using string-output-visitor to qobject_to_json_pretty,
  drop string-output-visitor patch.
---
 hmp-commands.hx | 13 +++++++++++++
 hmp.c           | 26 ++++++++++++++++++++++++++
 hmp.h           |  1 +
 3 files changed, 40 insertions(+)

diff --git a/hmp-commands.hx b/hmp-commands.hx
index 848efee..73f0372 100644
--- a/hmp-commands.hx
+++ b/hmp-commands.hx
@@ -1736,6 +1736,19 @@ Print QOM properties of object at location @var{path}
 ETEXI
 
     {
+        .name       = "qom-get",
+        .args_type  = "path:s,property:s",
+        .params     = "path property",
+        .help       = "print QOM property",
+        .mhandler.cmd  = hmp_qom_get,
+    },
+
+STEXI
+@item qom-get @var{path} @var{property}
+Print QOM property @var{property} of object at location @var{path}
+ETEXI
+
+    {
         .name       = "qom-set",
         .args_type  = "path:s,property:s,value:s",
         .params     = "path property value",
diff --git a/hmp.c b/hmp.c
index cc2056e..88c659b 100644
--- a/hmp.c
+++ b/hmp.c
@@ -22,11 +22,13 @@
 #include "qemu/option.h"
 #include "qemu/timer.h"
 #include "qmp-commands.h"
+#include "qom/qom-qobject.h"
 #include "qemu/sockets.h"
 #include "monitor/monitor.h"
 #include "monitor/qdev.h"
 #include "qapi/opts-visitor.h"
 #include "qapi/qmp/qerror.h"
+#include "qapi/qmp/qjson.h"
 #include "qapi/string-output-visitor.h"
 #include "qapi/util.h"
 #include "qapi-visit.h"
@@ -2064,6 +2066,30 @@ void hmp_qom_list(Monitor *mon, const QDict *qdict)
     hmp_handle_error(mon, &err);
 }
 
+void hmp_qom_get(Monitor *mon, const QDict *qdict)
+{
+    const char *path = qdict_get_str(qdict, "path");
+    const char *property = qdict_get_str(qdict, "property");
+    Error *err = NULL;
+    Object *obj;
+    QObject *sub;
+
+    obj = object_resolve_path(path, NULL);
+    if (obj == NULL) {
+        error_set(&err, ERROR_CLASS_DEVICE_NOT_FOUND,
+                  "Device '%s' not found", path);
+        hmp_handle_error(mon, &err);
+        return;
+    }
+    sub = object_property_get_qobject(obj, property, &err);
+    if (err == NULL) {
+        QString *str = qobject_to_json_pretty(sub);
+        monitor_printf(mon, "%s\n", qstring_get_str(str));
+        QDECREF(str);
+    }
+    hmp_handle_error(mon, &err);
+}
+
 void hmp_qom_set(Monitor *mon, const QDict *qdict)
 {
     const char *path = qdict_get_str(qdict, "path");
diff --git a/hmp.h b/hmp.h
index 0876ec0..882f339 100644
--- a/hmp.h
+++ b/hmp.h
@@ -103,6 +103,7 @@ void hmp_object_del(Monitor *mon, const QDict *qdict);
 void hmp_info_memdev(Monitor *mon, const QDict *qdict);
 void hmp_info_memory_devices(Monitor *mon, const QDict *qdict);
 void hmp_qom_list(Monitor *mon, const QDict *qdict);
+void hmp_qom_get(Monitor *mon, const QDict *qdict);
 void hmp_qom_set(Monitor *mon, const QDict *qdict);
 void object_add_completion(ReadLineState *rs, int nb_args, const char *str);
 void object_del_completion(ReadLineState *rs, int nb_args, const char *str);
-- 
2.7.4