[Qemu-devel] [PATCH v2 2/2] Add dbus-vmstate object

[Marc-André Lureau]

When instanciated, this object will connect to the given D-Bus
bus. During migration, it will take the data from org.qemu.VMState1
instances.

See documentation for further details.

Signed-off-by: Marc-André Lureau <address@hidden>
---
 MAINTAINERS                   |   6 +
 backends/Makefile.objs        |   4 +
 backends/dbus-vmstate.c       | 332 ++++++++++++++++++++++++++++++
 configure                     |   7 +
 docs/interop/dbus-vmstate.rst |  63 ++++++
 docs/interop/index.rst        |   1 +
 tests/Makefile.include        |  18 +-
 tests/dbus-vmstate-test.c     | 371 ++++++++++++++++++++++++++++++++++
 tests/dbus-vmstate1.xml       |  12 ++
 9 files changed, 813 insertions(+), 1 deletion(-)
 create mode 100644 backends/dbus-vmstate.c
 create mode 100644 docs/interop/dbus-vmstate.rst
 create mode 100644 tests/dbus-vmstate-test.c
 create mode 100644 tests/dbus-vmstate1.xml

diff --git a/MAINTAINERS b/MAINTAINERS
index d6de200453..d136bf4f4b 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2143,6 +2143,12 @@ F: tests/migration-test.c
 F: docs/devel/migration.rst
 F: qapi/migration.json
 
+DBus VMState
+M: Marc-André Lureau <address@hidden>
+S: Maintained
+F: backends/dbus-vmstate.c
+F: tests/dbus-vmstate*
+
 Seccomp
 M: Eduardo Otubo <address@hidden>
 S: Supported
diff --git a/backends/Makefile.objs b/backends/Makefile.objs
index 981e8e122f..dbbe12b225 100644
--- a/backends/Makefile.objs
+++ b/backends/Makefile.objs
@@ -17,3 +17,7 @@ endif
 common-obj-$(call land,$(CONFIG_VHOST_USER),$(CONFIG_VIRTIO)) += vhost-user.o
 
 common-obj-$(CONFIG_LINUX) += hostmem-memfd.o
+
+common-obj-$(CONFIG_GIO) += dbus-vmstate.o
+dbus-vmstate.o-cflags = $(GIO_CFLAGS)
+dbus-vmstate.o-libs = $(GIO_LIBS)
diff --git a/backends/dbus-vmstate.c b/backends/dbus-vmstate.c
new file mode 100644
index 0000000000..a9d9cac388
--- /dev/null
+++ b/backends/dbus-vmstate.c
@@ -0,0 +1,332 @@
+/*
+ * QEMU dbus-vmstate
+ *
+ * Copyright (C) 2019 Red Hat Inc
+ *
+ * Authors:
+ *  Marc-André Lureau <address@hidden>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/error-report.h"
+#include "qapi/error.h"
+#include "qom/object_interfaces.h"
+#include "qapi/qmp/qerror.h"
+#include "migration/register.h"
+#include "migration/qemu-file-types.h"
+#include <gio/gio.h>
+
+typedef struct DBusVMState DBusVMState;
+typedef struct DBusVMStateClass DBusVMStateClass;
+
+#define TYPE_DBUS_VMSTATE "dbus-vmstate"
+#define DBUS_VMSTATE(obj)                                \
+    OBJECT_CHECK(DBusVMState, (obj), TYPE_DBUS_VMSTATE)
+#define DBUS_VMSTATE_GET_CLASS(obj)                              \
+    OBJECT_GET_CLASS(DBusVMStateClass, (obj), TYPE_DBUS_VMSTATE)
+#define DBUS_VMSTATE_CLASS(klass)                                    \
+    OBJECT_CLASS_CHECK(DBusVMStateClass, (klass), TYPE_DBUS_VMSTATE)
+
+struct DBusVMStateClass {
+    ObjectClass parent_class;
+};
+
+struct DBusVMState {
+    Object parent;
+
+    GDBusConnection *bus;
+    GDBusProxy *proxy;
+    char *id;
+    char *dbus_addr;
+};
+
+static const GDBusPropertyInfo vmstate_property_info[] = {
+    { -1, (char *) "Id", (char *) "s",
+      G_DBUS_PROPERTY_INFO_FLAGS_READABLE, NULL },
+};
+
+static const GDBusPropertyInfo * const vmstate_property_info_pointers[] = {
+    &vmstate_property_info[0],
+    NULL
+};
+
+static const GDBusInterfaceInfo vmstate1_interface_info = {
+    -1,
+    (char *) "org.qemu.VMState1",
+    (GDBusMethodInfo **) NULL,
+    (GDBusSignalInfo **) NULL,
+    (GDBusPropertyInfo **) &vmstate_property_info_pointers,
+    NULL,
+};
+
+#define DBUS_VMSTATE_SIZE_LIMIT (1 << 20) /* 1mb */
+
+
+static char *
+get_idstr(DBusVMState *self)
+{
+    return g_strdup_printf("%s-%s", TYPE_DBUS_VMSTATE, self->id);
+}
+
+static char *
+dbus_proxy_get_id(GDBusProxy *proxy, GError **err)
+{
+    char *id = NULL;
+    GVariant *result = NULL;
+    size_t size;
+
+    result = g_dbus_proxy_get_cached_property(proxy, "Id");
+    if (!result) {
+        g_set_error_literal(err, G_IO_ERROR, G_IO_ERROR_FAILED,
+                            "Failed to get Id property");
+        return NULL;
+    }
+
+    id = g_variant_dup_string(result, &size);
+    g_clear_pointer(&result, g_variant_unref);
+
+    if (size == 0 || size >= 256) {
+        g_set_error_literal(err, G_IO_ERROR, G_IO_ERROR_FAILED,
+                            "Invalid Id property");
+        g_free(id);
+        return NULL;
+    }
+
+    return id;
+}
+
+static int
+dbus_load_state_proxy(GDBusProxy *proxy, const uint8_t *data, size_t size)
+{
+    GError *err = NULL;
+    GVariant *value, *result;
+    int ret = -1;
+
+    value = g_variant_new_fixed_array(G_VARIANT_TYPE_BYTE,
+                                      data, size, sizeof(char));
+    result = g_dbus_proxy_call_sync(proxy, "Load",
+                                    g_variant_new("(@ay)", value),
+                                    G_DBUS_CALL_FLAGS_NO_AUTO_START,
+                                    -1, NULL, &err);
+    if (!result) {
+        error_report("Failed to Load: %s", err->message);
+        goto end;
+    }
+
+    ret = 0;
+
+end:
+    g_clear_pointer(&result, g_variant_unref);
+    g_clear_error(&err);
+    return ret;
+}
+
+static int
+dbus_load_state(QEMUFile *f, void *opaque, int version_id)
+{
+    DBusVMState *self = DBUS_VMSTATE(opaque);
+    uint8_t *data = NULL;
+    int ret = -1;
+    char id[256];
+    unsigned int size;
+
+    if (qemu_get_counted_string(f, id) == 0) {
+        error_report("Invalid vmstate Id");
+        goto end;
+    }
+
+    if (g_strcmp0(id, self->id)) {
+        error_report("Invalid vmstate Id: %s != %s", id, self->id);
+        goto end;
+    }
+
+    size = qemu_get_be32(f);
+    if (size > DBUS_VMSTATE_SIZE_LIMIT) {
+        error_report("Invalid vmstate size: %u", size);
+        goto end;
+    }
+
+    data = g_malloc(size);
+    if (qemu_get_buffer(f, data, size) != size) {
+        error_report("Failed to read %u bytes", size);
+        goto end;
+    }
+
+    if (dbus_load_state_proxy(self->proxy, data, size) < 0) {
+        error_report("Failed to restore Id '%s'", id);
+        goto end;
+    }
+
+    ret = 0;
+
+end:
+    g_clear_pointer(&data, g_free);
+    return ret;
+}
+
+static void
+dbus_save_state(QEMUFile *f, void *opaque)
+{
+    DBusVMState *self = DBUS_VMSTATE(opaque);
+    GVariant *result = NULL, *child = NULL;
+    const uint8_t *data;
+    size_t size;
+    GError *err = NULL;
+
+    result = g_dbus_proxy_call_sync(self->proxy, "Save",
+                                    NULL, G_DBUS_CALL_FLAGS_NO_AUTO_START,
+                                    -1, NULL, &err);
+    if (!result) {
+        error_report("Failed to Save: %s", err->message);
+        g_clear_error(&err);
+        goto end;
+    }
+
+    child = g_variant_get_child_value(result, 0);
+    data = g_variant_get_fixed_array(child, &size, sizeof(char));
+    if (!data) {
+        error_report("Failed to Save: not a byte array");
+        goto end;
+    }
+    if (size > DBUS_VMSTATE_SIZE_LIMIT) {
+        error_report("Too much vmstate data to save: %zu", size);
+        goto end;
+    }
+
+    qemu_put_counted_string(f, self->id);
+    qemu_put_be32(f, size);
+    qemu_put_buffer(f, data, size);
+
+end:
+    g_clear_pointer(&child, g_variant_unref);
+    g_clear_pointer(&result, g_variant_unref);
+}
+
+static const SaveVMHandlers savevm_handlers = {
+    .save_state = dbus_save_state,
+    .load_state = dbus_load_state,
+};
+
+static void
+dbus_vmstate_complete(UserCreatable *uc, Error **errp)
+{
+    DBusVMState *self = DBUS_VMSTATE(uc);
+    GError *err = NULL;
+    GDBusConnection *bus = NULL;
+    GDBusProxy *proxy = NULL;
+    char *idstr = NULL;
+
+    if (!self->dbus_addr) {
+        error_setg(errp, QERR_MISSING_PARAMETER, "addr");
+        return;
+    }
+
+    bus = g_dbus_connection_new_for_address_sync(self->dbus_addr,
+               G_DBUS_CONNECTION_FLAGS_AUTHENTICATION_CLIENT,
+               NULL, NULL, &err);
+    if (err) {
+        error_setg(errp, "failed to connect to DBus: '%s'", err->message);
+        g_clear_error(&err);
+        return;
+    }
+
+    self->bus = bus;
+
+    proxy = g_dbus_proxy_new_sync(bus,
+                G_DBUS_PROXY_FLAGS_NONE,
+                (GDBusInterfaceInfo *) &vmstate1_interface_info,
+                NULL,
+                "/org/qemu/VMState1",
+                "org.qemu.VMState1",
+                NULL, &err);
+
+    if (err) {
+        error_setg(errp, "failed to create DBus proxy: '%s'", err->message);
+        g_clear_error(&err);
+        return;
+    }
+
+    self->proxy = proxy;
+
+    self->id = dbus_proxy_get_id(proxy, &err);
+    if (!self->id) {
+        error_setg(errp, "failed to get DBus Id: '%s'", err->message);
+        g_clear_error(&err);
+        return;
+    }
+
+    idstr = get_idstr(self);
+    if (register_savevm_live(NULL, idstr, 0, 0,
+                             &savevm_handlers, self) < 0) {
+        error_setg(errp, "Failed to register savevm handler");
+    }
+    g_free(idstr);
+}
+
+static void
+dbus_vmstate_finalize(Object *o)
+{
+    DBusVMState *self = DBUS_VMSTATE(o);
+    char *idstr = get_idstr(self);
+
+    unregister_savevm(NULL, idstr, self);
+
+    g_clear_object(&self->bus);
+    g_clear_object(&self->proxy);
+    g_free(self->dbus_addr);
+    g_free(self->id);
+    g_free(idstr);
+}
+
+static char *
+get_dbus_addr(Object *o, Error **errp)
+{
+    DBusVMState *self = DBUS_VMSTATE(o);
+
+    return g_strdup(self->dbus_addr);
+}
+
+static void
+set_dbus_addr(Object *o, const char *str, Error **errp)
+{
+    DBusVMState *self = DBUS_VMSTATE(o);
+
+    g_free(self->dbus_addr);
+    self->dbus_addr = g_strdup(str);
+}
+
+static void
+dbus_vmstate_class_init(ObjectClass *oc, void *data)
+{
+    UserCreatableClass *ucc = USER_CREATABLE_CLASS(oc);
+
+    ucc->complete = dbus_vmstate_complete;
+
+    object_class_property_add_str(oc, "addr",
+                                  get_dbus_addr, set_dbus_addr,
+                                  &error_abort);
+}
+
+static const TypeInfo dbus_vmstate_info = {
+    .name = TYPE_DBUS_VMSTATE,
+    .parent = TYPE_OBJECT,
+    .instance_size = sizeof(DBusVMState),
+    .instance_finalize = dbus_vmstate_finalize,
+    .class_size = sizeof(DBusVMStateClass),
+    .class_init = dbus_vmstate_class_init,
+    .interfaces = (InterfaceInfo[]) {
+        { TYPE_USER_CREATABLE },
+        { }
+    }
+};
+
+static void
+register_types(void)
+{
+    type_register_static(&dbus_vmstate_info);
+}
+
+type_init(register_types);
diff --git a/configure b/configure
index 714e7fb6a1..e5b34f5ca7 100755
--- a/configure
+++ b/configure
@@ -3665,10 +3665,16 @@ if $pkg_config --atleast-version=$glib_req_ver gio-2.0; 
then
     gio=yes
     gio_cflags=$($pkg_config --cflags gio-2.0)
     gio_libs=$($pkg_config --libs gio-2.0)
+    gdbus_codegen=$($pkg_config --variable=gdbus_codegen gio-2.0)
 else
     gio=no
 fi
 
+if $pkg_config --atleast-version=$glib_req_ver gio-unix-2.0; then
+    gio_cflags="$gio_cflags $($pkg_config --cflags gio-unix-2.0)"
+    gio_libs="$gio_libs $($pkg_config --libs gio-unix-2.0)"
+fi
+
 # Sanity check that the current size_t matches the
 # size that glib thinks it should be. This catches
 # problems on multi-arch where people try to build
@@ -6830,6 +6836,7 @@ if test "$gio" = "yes" ; then
     echo "CONFIG_GIO=y" >> $config_host_mak
     echo "GIO_CFLAGS=$gio_cflags" >> $config_host_mak
     echo "GIO_LIBS=$gio_libs" >> $config_host_mak
+    echo "GDBUS_CODEGEN=$gdbus_codegen" >> $config_host_mak
 fi
 echo "CONFIG_TLS_PRIORITY=\"$tls_priority\"" >> $config_host_mak
 if test "$gnutls" = "yes" ; then
diff --git a/docs/interop/dbus-vmstate.rst b/docs/interop/dbus-vmstate.rst
new file mode 100644
index 0000000000..4a32a183fb
--- /dev/null
+++ b/docs/interop/dbus-vmstate.rst
@@ -0,0 +1,63 @@
+============
+DBus VMState
+============
+
+Introduction
+============
+
+Helper processes may have their state migrated with the help of
+QEMU "dbus-vmstate" objects.
+
+At this point, the connection to the helper is done in DBus
+peer-to-peer mode (no initial Hello, and no bus name for
+communication). The helper must be listening to the given address.
+
+Helper may save arbitrary data to be transferred in the migration
+stream and restored/loaded on destination.
+
+The data amount to be transferred is limited to 1Mb. The state must be
+saved quickly (a few seconds maximum). (DBus imposes a time limit on
+reply anyway, and migration would fail if the data isn't given quickly
+enough)
+
+Interface
+=========
+
+On /org/qemu/VMState1 object path:
+
+.. code:: xml
+
+  <interface name="org.qemu.VMState1">
+    <property name="Id" type="s" access="read"/>
+    <method name="Load">
+      <arg type="ay" name="data" direction="in"/>
+    </method>
+    <method name="Save">
+      <arg type="ay" name="data" direction="out"/>
+    </method>
+  </interface>
+
+"Id" property
+-------------
+
+A utf8 encoded string that identifies the helper uniquely.
+Must be <256 bytes.
+
+Load(in u8[] bytes) method
+--------------------------
+
+The method called on destination with the state to restore.
+
+The helper may be initially started in a waiting state (with
+an --incoming argument for example), and it may resume on load
+success.
+
+An error may be returned to the caller.
+
+Save(out u8[] bytes) method
+---------------------------
+
+The method called on the source to get the current state to be
+migrated. The helper should continue to run normally.
+
+An error may be returned to the caller.
diff --git a/docs/interop/index.rst b/docs/interop/index.rst
index b4bfcab417..6bb173cfa6 100644
--- a/docs/interop/index.rst
+++ b/docs/interop/index.rst
@@ -13,6 +13,7 @@ Contents:
    :maxdepth: 2
 
    bitmaps
+   dbus-vmstate
    live-block-operations
    pr-helper
    vhost-user
diff --git a/tests/Makefile.include b/tests/Makefile.include
index fd7fdb8658..2c610086a7 100644
--- a/tests/Makefile.include
+++ b/tests/Makefile.include
@@ -157,7 +157,9 @@ check-qtest-pci-$(CONFIG_RTL8139_PCI) += 
tests/rtl8139-test$(EXESUF)
 check-qtest-pci-$(CONFIG_VGA) += tests/display-vga-test$(EXESUF)
 check-qtest-pci-$(CONFIG_HDA) += tests/intel-hda-test$(EXESUF)
 check-qtest-pci-$(CONFIG_IVSHMEM_DEVICE) += tests/ivshmem-test$(EXESUF)
-
+ifneq ($(GDBUS_CODEGEN),)
+check-qtest-pci-$(CONFIG_GIO) += tests/dbus-vmstate-test$(EXESUF)
+endif
 check-qtest-i386-$(CONFIG_ISA_TESTDEV) = tests/endianness-test$(EXESUF)
 check-qtest-i386-y += tests/fdc-test$(EXESUF)
 check-qtest-i386-y += tests/ide-test$(EXESUF)
@@ -618,6 +620,18 @@ tests/qapi-schema/doc-good.test.texi: 
$(SRC_PATH)/tests/qapi-schema/doc-good.jso
        @mv tests/qapi-schema/doc-good-qapi-doc.texi $@
        @rm -f tests/qapi-schema/doc-good-qapi-*.[ch] 
tests/qapi-schema/doc-good-qmp-*.[ch]
 
+tests/dbus-vmstate1.h tests/dbus-vmstate1.c: tests/dbus-vmstate1-gen-timestamp 
;
+tests/dbus-vmstate1-gen-timestamp: $(SRC_PATH)/tests/dbus-vmstate1.xml
+       $(call quiet-command,$(GDBUS_CODEGEN) $< \
+               --interface-prefix org.qemu --generate-c-code 
tests/dbus-vmstate1, \
+               "GEN","$(@:%-timestamp=%)")
+       @>$@
+
+tests/dbus-vmstate1.o-cflags := $(GIO_CFLAGS)
+tests/dbus-vmstate1.o-libs := $(GIO_LIBS)
+
+tests/dbus-vmstate-test.o: tests/dbus-vmstate1.h
+
 tests/test-string-output-visitor$(EXESUF): tests/test-string-output-visitor.o 
$(test-qapi-obj-y)
 tests/test-string-input-visitor$(EXESUF): tests/test-string-input-visitor.o 
$(test-qapi-obj-y)
 tests/test-qmp-event$(EXESUF): tests/test-qmp-event.o $(test-qapi-obj-y) 
tests/test-qapi-events.o
@@ -820,6 +834,7 @@ tests/test-filter-mirror$(EXESUF): 
tests/test-filter-mirror.o $(qtest-obj-y)
 tests/test-filter-redirector$(EXESUF): tests/test-filter-redirector.o 
$(qtest-obj-y)
 tests/test-x86-cpuid-compat$(EXESUF): tests/test-x86-cpuid-compat.o 
$(qtest-obj-y)
 tests/ivshmem-test$(EXESUF): tests/ivshmem-test.o 
contrib/ivshmem-server/ivshmem-server.o $(libqos-pc-obj-y) $(libqos-spapr-obj-y)
+tests/dbus-vmstate-test$(EXESUF): tests/dbus-vmstate-test.o 
tests/dbus-vmstate1.o $(libqos-pc-obj-y) $(libqos-spapr-obj-y)
 tests/vhost-user-bridge$(EXESUF): tests/vhost-user-bridge.o $(test-util-obj-y) 
libvhost-user.a
 tests/test-uuid$(EXESUF): tests/test-uuid.o $(test-util-obj-y)
 tests/test-arm-mptimer$(EXESUF): tests/test-arm-mptimer.o
@@ -1172,6 +1187,7 @@ check-clean:
        rm -rf $(check-unit-y) tests/*.o $(QEMU_IOTESTS_HELPERS-y)
        rm -rf $(sort $(foreach target,$(SYSEMU_TARGET_LIST), 
$(check-qtest-$(target)-y)) $(check-qtest-generic-y))
        rm -f tests/test-qapi-gen-timestamp
+       rm -f tests/dbus-vmstate1-gen-timestamp
        rm -rf $(TESTS_VENV_DIR) $(TESTS_RESULTS_DIR)
 
 clean: check-clean
diff --git a/tests/dbus-vmstate-test.c b/tests/dbus-vmstate-test.c
new file mode 100644
index 0000000000..45d44916d2
--- /dev/null
+++ b/tests/dbus-vmstate-test.c
@@ -0,0 +1,371 @@
+#include "qemu/osdep.h"
+#include <glib/gstdio.h>
+#include <gio/gio.h>
+#include "libqtest.h"
+#include "qemu-common.h"
+#include "dbus-vmstate1.h"
+
+static char *workdir;
+
+typedef struct TestServerId {
+    const char *name;
+    const char *data;
+    size_t size;
+} TestServerId;
+
+static const TestServerId idA = {
+    "idA", "I'am\0idA!", sizeof("I'am\0idA!")
+};
+
+static const TestServerId idB = {
+    "idB", "I'am\0idB!", sizeof("I'am\0idB!")
+};
+
+typedef struct TestServer {
+    const TestServerId *id;
+    bool save_called;
+    bool load_called;
+    GDBusObjectManagerServer *om;
+    GDBusServer *server;
+} TestServer;
+
+typedef struct Test {
+    bool migrate_fail;
+    TestServer srcA;
+    TestServer dstA;
+    TestServer srcB;
+    TestServer dstB;
+    GMainLoop *loop, *dbus_loop;
+    QTestState *src_qemu;
+} Test;
+
+GMutex mutex;
+GCond cond;
+
+static gboolean
+vmstate_load(VMState1 *object, GDBusMethodInvocation *invocation,
+             const gchar *arg_data, gpointer user_data)
+{
+    TestServer *h = user_data;
+    GVariant *args, *var;
+    const uint8_t *data;
+    size_t size;
+
+    args = g_dbus_method_invocation_get_parameters(invocation);
+    var = g_variant_get_child_value(args, 0);
+    data = g_variant_get_fixed_array(var, &size, sizeof(char));
+    g_assert_cmpuint(size, ==, h->id->size);
+    g_assert(!memcmp(data, h->id->data, h->id->size));
+    h->load_called = true;
+    g_variant_unref(var);
+
+    g_dbus_method_invocation_return_value(invocation, g_variant_new("()"));
+    return TRUE;
+}
+
+static gboolean
+vmstate_save(VMState1 *object, GDBusMethodInvocation *invocation,
+             gpointer user_data)
+{
+    TestServer *h = user_data;
+    GVariant *var;
+
+    var = g_variant_new_fixed_array(G_VARIANT_TYPE_BYTE,
+                                    h->id->data, h->id->size, sizeof(char));
+    g_dbus_method_invocation_return_value(invocation,
+                                          g_variant_new("(@ay)", var));
+    h->save_called = true;
+
+    return TRUE;
+}
+
+static void
+connection_closed(GDBusConnection *connection,
+                  gboolean remote_peer_vanished,
+                  GError *Error,
+                  gpointer user_data)
+{
+    TestServer *h = user_data;
+
+    g_clear_object(&h->om);
+    g_clear_object(&connection);
+}
+
+static GDBusObjectManagerServer *
+get_omserver(GDBusConnection *conn, gpointer user_data)
+{
+    TestServer *h = user_data;
+    GDBusObjectManagerServer *om;
+    GDBusObjectSkeleton *sk;
+    VMState1 *v;
+
+    om = g_dbus_object_manager_server_new("/org/qemu");
+    sk = g_dbus_object_skeleton_new("/org/qemu/VMState1");
+
+    v = vmstate1_skeleton_new();
+    g_object_set(v, "id", h->id->name, NULL);
+    g_signal_connect(v, "handle-load", G_CALLBACK(vmstate_load), user_data);
+    g_signal_connect(v, "handle-save", G_CALLBACK(vmstate_save), user_data);
+
+    g_dbus_object_skeleton_add_interface(sk, G_DBUS_INTERFACE_SKELETON(v));
+    g_dbus_object_manager_server_export(om, sk);
+    g_dbus_object_manager_server_set_connection(om, conn);
+
+    g_clear_object(&v);
+    g_clear_object(&sk);
+
+    return om;
+}
+
+static gboolean
+on_new_connection(GDBusServer *server,
+                  GDBusConnection *connection,
+                  gpointer user_data)
+{
+    TestServer *h = user_data;
+
+    g_object_ref(connection);
+    g_signal_connect(connection, "closed",
+                     G_CALLBACK(connection_closed), user_data);
+    h->om = get_omserver(connection, user_data);
+
+    return TRUE;
+}
+
+static gboolean
+allow_mechanism_cb(GDBusAuthObserver *observer,
+                   const gchar *mechanism,
+                   gpointer user_data)
+{
+    return g_strcmp0(mechanism, "EXTERNAL") == 0;
+}
+
+static gboolean
+authorize_authenticated_peer_cb(GDBusAuthObserver *observer,
+                                GIOStream *stream,
+                                GCredentials *credentials,
+                                gpointer user_data)
+{
+    gboolean authorized = FALSE;
+
+    if (credentials != NULL) {
+        GCredentials *own_credentials = g_credentials_new();
+
+        if (g_credentials_is_same_user(credentials, own_credentials, NULL)) {
+            authorized = TRUE;
+        }
+
+        g_clear_object(&own_credentials);
+    }
+
+    return authorized;
+}
+
+static GDBusServer *
+server_start(TestServer *h, const char *p, const TestServerId *id)
+{
+    GDBusAuthObserver *observer = NULL;
+    GDBusServer *server = NULL;
+    gchar *guid = NULL;
+    GError *error = NULL;
+    char *addr = NULL;
+
+    h->id = id;
+    addr = g_strdup_printf("unix:path=%s/dbus-%s%s", workdir, p, h->id->name);
+    guid = g_dbus_generate_guid();
+    observer = g_dbus_auth_observer_new();
+    g_signal_connect(observer, "allow-mechanism",
+                     G_CALLBACK(allow_mechanism_cb), h);
+    g_signal_connect(observer, "authorize-authenticated-peer",
+                     G_CALLBACK(authorize_authenticated_peer_cb), h);
+
+    server = g_dbus_server_new_sync(addr,
+                                    G_DBUS_SERVER_FLAGS_NONE,
+                                    guid,
+                                    observer,
+                                    NULL, /* GCancellable */
+                                    &error);
+    g_dbus_server_start(server);
+    g_clear_object(&observer);
+    g_free(guid);
+
+    if (server == NULL) {
+        g_printerr("Error creating server at address %s: %s\n",
+                   addr, error->message);
+        g_error_free(error);
+        return NULL;
+    }
+
+    g_signal_connect(server, "new-connection",
+                     G_CALLBACK(on_new_connection), h);
+
+    g_free(addr);
+    return server;
+}
+
+
+static gpointer
+dbus_thread(gpointer p)
+{
+    Test *test = p;
+    GMainContext *context = g_main_context_new();
+    GMainLoop *loop = g_main_loop_new(context, FALSE);
+
+    g_main_context_push_thread_default(context);
+
+    g_mutex_lock(&mutex);
+    test->srcA.server = server_start(&test->srcA, "src", &idA);
+    test->srcB.server = server_start(&test->srcB, "src", &idB);
+    test->dstA.server = server_start(&test->dstA, "dst", &idA);
+    test->dstB.server = server_start(&test->dstB, "dst", &idB);
+    test->dbus_loop = loop;
+    g_cond_signal(&cond);
+    g_mutex_unlock(&mutex);
+
+    g_main_loop_run(loop);
+
+    g_main_loop_unref(loop);
+    g_main_context_unref(context);
+
+    g_mutex_lock(&mutex);
+    g_clear_object(&test->srcA.server);
+    g_clear_object(&test->srcB.server);
+    g_clear_object(&test->dstA.server);
+    g_clear_object(&test->dstB.server);
+    g_mutex_unlock(&mutex);
+
+    return NULL;
+}
+
+static gboolean
+wait_for_migration_complete(gpointer user_data)
+{
+    Test *test = user_data;
+    QDict *rsp_return;
+    bool stop = false;
+    const char *status;
+
+    qtest_qmp_send(test->src_qemu, "{ 'execute': 'query-migrate' }");
+    rsp_return = qtest_qmp_receive_success(test->src_qemu, NULL, NULL);
+    status = qdict_get_str(rsp_return, "status");
+    if (g_str_equal(status, "completed") || g_str_equal(status, "failed")) {
+        stop = true;
+        g_assert_cmpstr(status, ==,
+                        test->migrate_fail ? "failed" : "completed");
+    }
+    qobject_unref(rsp_return);
+
+    if (stop) {
+        g_main_loop_quit(test->loop);
+    }
+    return stop ? G_SOURCE_REMOVE : G_SOURCE_CONTINUE;
+}
+
+static void migrate(QTestState *who, const char *uri)
+{
+    QDict *args, *rsp;
+
+    args = qdict_new();
+    qdict_put_str(args, "uri", uri);
+
+    rsp = qtest_qmp(who, "{ 'execute': 'migrate', 'arguments': %p }", args);
+
+    g_assert(qdict_haskey(rsp, "return"));
+    qobject_unref(rsp);
+}
+
+static void
+test_dbus_vmstate(Test *test)
+{
+    QTestState *src_qemu = NULL, *dst_qemu = NULL;
+    char *src_qemu_args = NULL, *dst_qemu_args = NULL;
+    char *uri = g_strdup_printf("unix:%s/migsocket", workdir);
+    GThread *t = g_thread_new("dbus", dbus_thread, test);
+
+    g_mutex_lock(&mutex);
+    while (!test->dbus_loop) {
+        g_cond_wait(&cond, &mutex);
+    }
+
+    src_qemu_args =
+        g_strdup_printf("-object dbus-vmstate,id=dvA,addr=%s "
+                        "-object dbus-vmstate,id=dvB,addr=%s",
+                        g_dbus_server_get_client_address(test->srcA.server),
+                        g_dbus_server_get_client_address(test->srcB.server));
+
+
+    dst_qemu_args =
+        g_strdup_printf("-object dbus-vmstate,id=dvA,addr=%s "
+                        "-object dbus-vmstate,id=dvB,addr=%s "
+                        "-incoming %s",
+                        g_dbus_server_get_client_address(test->dstA.server),
+                        g_dbus_server_get_client_address(test->dstB.server),
+                        uri);
+
+    src_qemu = qtest_init(src_qemu_args);
+    dst_qemu = qtest_init(dst_qemu_args);
+
+    test->loop = g_main_loop_new(NULL, TRUE);
+
+    migrate(src_qemu, uri);
+    test->src_qemu = src_qemu;
+    g_timeout_add_seconds(1, wait_for_migration_complete, test);
+
+    g_main_loop_run(test->loop);
+    g_main_loop_unref(test->loop);
+
+    g_free(uri);
+    qtest_quit(dst_qemu);
+    qtest_quit(src_qemu);
+    g_free(dst_qemu_args);
+    g_free(src_qemu_args);
+
+    g_main_loop_quit(test->dbus_loop);
+    g_mutex_unlock(&mutex);
+
+    g_thread_join(t);
+}
+
+static void
+check_migrated(TestServer *s, TestServer *d)
+{
+    assert(s->save_called);
+    assert(!s->load_called);
+    assert(!d->save_called);
+    assert(d->load_called);
+}
+
+static void
+test_dbus_vmstate_migrate(void)
+{
+    Test test = { };
+
+    test_dbus_vmstate(&test);
+
+    check_migrated(&test.srcA, &test.dstA);
+    check_migrated(&test.srcB, &test.dstB);
+}
+
+int
+main(int argc, char **argv)
+{
+    GError *err = NULL;
+    int ret;
+
+    g_test_init(&argc, &argv, NULL);
+
+    workdir = g_dir_make_tmp("dbus-vmstate-test-XXXXXX", &err);
+    if (!workdir) {
+        g_error("Unable to create temporary dir: %s\n", err->message);
+    }
+
+    qtest_add_func("/dbus-vmstate/migrate",
+                   test_dbus_vmstate_migrate);
+
+    ret = g_test_run();
+
+    rmdir(workdir);
+    g_free(workdir);
+
+    return ret;
+}
diff --git a/tests/dbus-vmstate1.xml b/tests/dbus-vmstate1.xml
new file mode 100644
index 0000000000..cc8563be4c
--- /dev/null
+++ b/tests/dbus-vmstate1.xml
@@ -0,0 +1,12 @@
+<?xml version="1.0"?>
+<node name="/" xmlns:doc="http://www.freedesktop.org/dbus/1.0/doc.dtd";>
+  <interface name="org.qemu.VMState1">
+    <property name="Id" type="s" access="read"/>
+    <method name="Load">
+      <arg type="ay" name="data" direction="in"/>
+    </method>
+    <method name="Save">
+      <arg type="ay" name="data" direction="out"/>
+    </method>
+  </interface>
+</node>
-- 
2.23.0.rc1