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

[Marc-André Lureau]

Hi

On Thu, Aug 8, 2019 at 7:03 PM Marc-André Lureau
<address@hidden> wrote:
>
> When instanciated, this object will connect to the given D-Bus
> bus. During migration, it will take the data from org.qemu.VMState1
> instances.

I forgot to update the commit message.

When instantiated, this object will connect to the given D-Bus peer.
During migration, it will load/save the data from the
org.qemu.VMState1 interface.

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
>