qdev: Display warning about unused -global

This can help a user understand why -global was ignored.

For example: with "-vga cirrus"; "-global vga.vgamem_mb=16" is just
ignored when "-global cirrus-vga.vgamem_mb=16" is not.

This is currently clear when the wrong property is provided:

out/x86_64-softmmu/qemu-system-x86_64 -global cirrus-vga.vram_size_mb=16 -monitor pty -vga cirrus
char device redirected to /dev/pts/20 (label compat_monitor0)
qemu-system-x86_64: Property '.vram_size_mb' not found
Aborted (core dumped)

vs

out/x86_64-softmmu/qemu-system-x86_64 -global vga.vram_size_mb=16 -monitor pty -vga cirrus
char device redirected to /dev/pts/20 (label compat_monitor0)
VNC server running on `::1:5900'
^Cqemu: terminating on signal 2

Signed-off-by: Don Slutz <dslutz@verizon.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>

hw/core/qdev-properties-system.c

@@ -439,11 +439,27 @@ PropertyInfo qdev_prop_iothread = {
 static int qdev_add_one_global(QemuOpts *opts, void *opaque)
 {
     GlobalProperty *g;
+    ObjectClass *oc;
 
     g = g_malloc0(sizeof(*g));
     g->driver   = qemu_opt_get(opts, "driver");
     g->property = qemu_opt_get(opts, "property");
     g->value    = qemu_opt_get(opts, "value");
+    oc = object_class_by_name(g->driver);
+    if (oc) {
+        DeviceClass *dc = DEVICE_CLASS(oc);
+
+        if (dc->hotpluggable) {
+            /* If hotpluggable then skip not_used checking. */
+            g->not_used = false;
+        } else {
+            /* Maybe a typo. */
+            g->not_used = true;
+        }
+    } else {
+        /* Maybe a typo. */
+        g->not_used = true;
+    }
     qdev_prop_register_global(g);
     return 0;
 }

hw/core/qdev-properties.c

@@ -955,6 +955,23 @@ void qdev_prop_register_global_list(GlobalProperty *props)
     }
 }
 
+int qdev_prop_check_global(void)
+{
+    GlobalProperty *prop;
+    int ret = 0;
+
+    QTAILQ_FOREACH(prop, &global_props, next) {
+        if (!prop->not_used) {
+            continue;
+        }
+        ret = 1;
+        error_report("Warning: \"-global %s.%s=%s\" not used",
+                     prop->driver, prop->property, prop->value);
+
+    }
+    return ret;
+}
+
 void qdev_prop_set_globals_for_type(DeviceState *dev, const char *typename,
                                     Error **errp)
 {
@@ -966,6 +983,7 @@ void qdev_prop_set_globals_for_type(DeviceState *dev, const char *typename,
         if (strcmp(typename, prop->driver) != 0) {
             continue;
         }
+        prop->not_used = false;
         object_property_parse(OBJECT(dev), prop->value, prop->property, &err);
         if (err != NULL) {
             error_propagate(errp, err);

include/hw/qdev-core.h

@@ -231,10 +231,18 @@ struct PropertyInfo {
     ObjectPropertyRelease *release;
 };
 
+/**
+ * GlobalProperty:
+ * @not_used: Track use of a global property.  Defaults to false in all C99
+ * struct initializations.
+ *
+ * This prevents reports of .compat_props when they are not used.
+ */
 typedef struct GlobalProperty {
     const char *driver;
     const char *property;
     const char *value;
+    bool not_used;
     QTAILQ_ENTRY(GlobalProperty) next;
 } GlobalProperty;
 

include/hw/qdev-properties.h

@@ -180,6 +180,7 @@ void qdev_prop_set_ptr(DeviceState *dev, const char *name, void *value);
 
 void qdev_prop_register_global(GlobalProperty *prop);
 void qdev_prop_register_global_list(GlobalProperty *props);
+int qdev_prop_check_global(void);
 void qdev_prop_set_globals(DeviceState *dev, Error **errp);
 void qdev_prop_set_globals_for_type(DeviceState *dev, const char *typename,
                                     Error **errp);

vl.c

@@ -4532,6 +4532,8 @@ int main(int argc, char **argv, char **envp)
         }
     }
 
+    qdev_prop_check_global();
+
     if (incoming) {
         Error *local_err = NULL;
         qemu_start_incoming_migration(incoming, &local_err);