util: add dbus helper unit

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

MAINTAINERS

@@ -2209,6 +2209,8 @@ F: qapi/migration.json
 D-Bus
 M: Marc-André Lureau <marcandre.lureau@redhat.com>
 S: Maintained
+F: util/dbus.c
+F: include/qemu/dbus.h
 F: docs/interop/dbus.rst
 
 Seccomp

include/qemu/dbus.h

@@ -0,0 +1,19 @@
+/*
+ * Helpers for using D-Bus
+ *
+ * Copyright (C) 2019 Red Hat, Inc.
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ */
+
+#ifndef DBUS_H
+#define DBUS_H
+
+#include <gio/gio.h>
+
+GStrv qemu_dbus_get_queued_owners(GDBusConnection *connection,
+                                  const char *name,
+                                  Error **errp);
+
+#endif /* DBUS_H */

util/Makefile.objs

@@ -56,3 +56,6 @@ util-obj-$(call lnot,$(CONFIG_INOTIFY1)) += filemonitor-stub.o
 util-obj-$(CONFIG_LINUX) += vfio-helpers.o
 util-obj-$(CONFIG_POSIX) += drm.o
 util-obj-y += guest-random.o
+util-obj-$(CONFIG_GIO) += dbus.o
+dbus.o-cflags = $(GIO_CFLAGS)
+dbus.o-libs = $(GIO_LIBS)

util/dbus.c

@@ -0,0 +1,57 @@
+/*
+ * Helpers for using D-Bus
+ *
+ * Copyright (C) 2019 Red Hat, Inc.
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/dbus.h"
+#include "qemu/error-report.h"
+#include "qapi/error.h"
+
+/*
+ * qemu_dbus_get_queued_owners() - return the list of queued unique names
+ * @connection: A GDBusConnection
+ * @name: a service name
+ *
+ * Return: a GStrv of unique names, or NULL on failure.
+ */
+GStrv
+qemu_dbus_get_queued_owners(GDBusConnection *connection, const char *name,
+                            Error **errp)
+{
+    g_autoptr(GDBusProxy) proxy = NULL;
+    g_autoptr(GVariant) result = NULL;
+    g_autoptr(GVariant) child = NULL;
+    g_autoptr(GError) err = NULL;
+
+    proxy = g_dbus_proxy_new_sync(connection, G_DBUS_PROXY_FLAGS_NONE, NULL,
+                                  "org.freedesktop.DBus",
+                                  "/org/freedesktop/DBus",
+                                  "org.freedesktop.DBus",
+                                  NULL, &err);
+    if (!proxy) {
+        error_setg(errp, "Failed to create DBus proxy: %s", err->message);
+        return NULL;
+    }
+
+    result = g_dbus_proxy_call_sync(proxy, "ListQueuedOwners",
+                                    g_variant_new("(s)", name),
+                                    G_DBUS_CALL_FLAGS_NO_AUTO_START,
+                                    -1, NULL, &err);
+    if (!result) {
+        if (g_error_matches(err,
+                            G_DBUS_ERROR,
+                            G_DBUS_ERROR_NAME_HAS_NO_OWNER)) {
+            return g_new0(char *, 1);
+        }
+        error_setg(errp, "Failed to call ListQueuedOwners: %s", err->message);
+        return NULL;
+    }
+
+    child = g_variant_get_child_value(result, 0);
+    return g_variant_dup_strv(child, NULL);
+}