We are going to implement backend-transfer feature: some devices
will be able to transfer their backend through migration stream
for local migration through UNIX domain socket. For example,
virtio-net will migrate its attached TAP netdev, with all its
connected file descriptors.
Let's add a command to list supporting devices (no one for now),
together with necessary infrastructure in qdev code.
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
---
include/hw/qdev-core.h | 7 +++++++
qapi/qdev.json | 26 +++++++++++++++++++++++++
system/qdev-monitor.c | 43 ++++++++++++++++++++++++++++++++++++++++++
3 files changed, 76 insertions(+)
diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
index 2caa0cbd26..0551fbaa6c 100644
--- a/include/hw/qdev-core.h
+++ b/include/hw/qdev-core.h
@@ -96,6 +96,7 @@ typedef void (*DeviceReset)(DeviceState *dev);
typedef void (*BusRealize)(BusState *bus, Error **errp);
typedef void (*BusUnrealize)(BusState *bus);
typedef int (*DeviceSyncConfig)(DeviceState *dev, Error **errp);
+typedef bool (*DeviceSupportBackendTransfer)(DeviceState *dev, Error **errp);
/**
* struct DeviceClass - The base class for all devices.
@@ -174,6 +175,12 @@ struct DeviceClass {
DeviceUnrealize unrealize;
DeviceSyncConfig sync_config;
+ /**
+ * @backend_transfer_support: reports support for backend-transfer
+ * migration of the device.
+ */
+ DeviceSupportBackendTransfer backend_transfer_support;
+
/**
* @vmsd: device state serialisation description for
* migration/save/restore
diff --git a/qapi/qdev.json b/qapi/qdev.json
index e14a0c9259..d7e878d58d 100644
--- a/qapi/qdev.json
+++ b/qapi/qdev.json
@@ -188,3 +188,29 @@
{ 'command': 'device-sync-config',
'features': [ 'unstable' ],
'data': {'id': 'str'} }
+
+##
+# @DevPath:
+#
+# @path: the device's QOM path
+#
+# Since: 10.2
+##
+{ 'struct': 'DevPath',
+ 'data': { 'path': 'str' } }
+
+##
+# @query-backend-transfer-support:
+#
+# Returns list of devices, supporting backend-transfer
+# migration.
+#
+# Features:
+#
+# @unstable: The command is experimental.
+#
+# Since: 10.2
+##
+{ 'command': 'query-backend-transfer-support',
+ 'features': [ 'unstable' ],
+ 'returns': [ 'DevPath' ] }
diff --git a/system/qdev-monitor.c b/system/qdev-monitor.c
index ec4a2394ce..9d3d961c15 100644
--- a/system/qdev-monitor.c
+++ b/system/qdev-monitor.c
@@ -939,6 +939,49 @@ void qmp_device_del(const char *id, Error **errp)
}
}
+static bool qdev_backend_transfer_support(DeviceState *dev, Error **errp)
+{
+ DeviceClass *dc = DEVICE_GET_CLASS(dev);
+
+ if (!dc->backend_transfer_support) {
+ error_setg(errp, "backend-transfer is not supported for '%s'",
+ object_get_typename(OBJECT(dev)));
+ return false;
+ }
+
+ return dc->backend_transfer_support(dev, errp);
+}
+
+static int qdev_add_if_backend_transfer_supported(Object *obj, void *opaque)
+{
+ DevPathList **list = opaque;
+ DeviceState *dev = (DeviceState *)object_dynamic_cast(obj, TYPE_DEVICE);
+
+ if (dev != NULL && qdev_backend_transfer_support(dev, NULL)) {
+ DevPath *el = g_new(DevPath, 1);
+ *el = (DevPath) {
+ .path = g_strdup(dev->canonical_path),
+ };
+ QAPI_LIST_PREPEND(*list, el);
+ }
+
+ /* Recursively check all children */
+ object_child_foreach(obj, qdev_add_if_backend_transfer_supported, opaque);
+
+ return 0;
+}
+
+DevPathList *qmp_query_backend_transfer_support(Error **errp)
+{
+ DevPathList *result = NULL;
+ Object *peripheral = machine_get_container("peripheral");
+
+ object_child_foreach(peripheral, qdev_add_if_backend_transfer_supported,
+ &result);
+
+ return result;
+}
+
int qdev_sync_config(DeviceState *dev, Error **errp)
{
DeviceClass *dc = DEVICE_GET_CLASS(dev);
--
2.48.1Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> writes:
> We are going to implement backend-transfer feature: some devices
> will be able to transfer their backend through migration stream
> for local migration through UNIX domain socket. For example,
> virtio-net will migrate its attached TAP netdev, with all its
> connected file descriptors.
>
> Let's add a command to list supporting devices (no one for now),
> together with necessary infrastructure in qdev code.
Use case?
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
> ---
> include/hw/qdev-core.h | 7 +++++++
> qapi/qdev.json | 26 +++++++++++++++++++++++++
> system/qdev-monitor.c | 43 ++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 76 insertions(+)
>
> diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
> index 2caa0cbd26..0551fbaa6c 100644
> --- a/include/hw/qdev-core.h
> +++ b/include/hw/qdev-core.h
> @@ -96,6 +96,7 @@ typedef void (*DeviceReset)(DeviceState *dev);
> typedef void (*BusRealize)(BusState *bus, Error **errp);
> typedef void (*BusUnrealize)(BusState *bus);
> typedef int (*DeviceSyncConfig)(DeviceState *dev, Error **errp);
> +typedef bool (*DeviceSupportBackendTransfer)(DeviceState *dev, Error **errp);
>
> /**
> * struct DeviceClass - The base class for all devices.
> @@ -174,6 +175,12 @@ struct DeviceClass {
> DeviceUnrealize unrealize;
> DeviceSyncConfig sync_config;
>
> + /**
> + * @backend_transfer_support: reports support for backend-transfer
> + * migration of the device.
> + */
> + DeviceSupportBackendTransfer backend_transfer_support;
> +
> /**
> * @vmsd: device state serialisation description for
> * migration/save/restore
> diff --git a/qapi/qdev.json b/qapi/qdev.json
> index e14a0c9259..d7e878d58d 100644
> --- a/qapi/qdev.json
> +++ b/qapi/qdev.json
> @@ -188,3 +188,29 @@
> { 'command': 'device-sync-config',
> 'features': [ 'unstable' ],
> 'data': {'id': 'str'} }
> +
> +##
> +# @DevPath:
> +#
> +# @path: the device's QOM path
> +#
> +# Since: 10.2
> +##
> +{ 'struct': 'DevPath',
> + 'data': { 'path': 'str' } }
> +
> +##
> +# @query-backend-transfer-support:
> +#
> +# Returns list of devices, supporting backend-transfer
> +# migration.
Suggest
# Return the devices that support backend-transfer migration.
> +#
> +# Features:
> +#
> +# @unstable: The command is experimental.
The conventional text ist "This command is experimental."
> +#
> +# Since: 10.2
> +##
> +{ 'command': 'query-backend-transfer-support',
> + 'features': [ 'unstable' ],
> + 'returns': [ 'DevPath' ] }
> diff --git a/system/qdev-monitor.c b/system/qdev-monitor.c
> index ec4a2394ce..9d3d961c15 100644
> --- a/system/qdev-monitor.c
> +++ b/system/qdev-monitor.c
> @@ -939,6 +939,49 @@ void qmp_device_del(const char *id, Error **errp)
> }
> }
>
> +static bool qdev_backend_transfer_support(DeviceState *dev, Error **errp)
> +{
> + DeviceClass *dc = DEVICE_GET_CLASS(dev);
> +
> + if (!dc->backend_transfer_support) {
> + error_setg(errp, "backend-transfer is not supported for '%s'",
> + object_get_typename(OBJECT(dev)));
> + return false;
> + }
> +
> + return dc->backend_transfer_support(dev, errp);
> +}
@errp is useless in this patch: the only caller passes NULL. Took me a
minute to check it doesn't remain useless. The next patch puts it to
use.
> +
> +static int qdev_add_if_backend_transfer_supported(Object *obj, void *opaque)
> +{
> + DevPathList **list = opaque;
> + DeviceState *dev = (DeviceState *)object_dynamic_cast(obj, TYPE_DEVICE);
> +
> + if (dev != NULL && qdev_backend_transfer_support(dev, NULL)) {
> + DevPath *el = g_new(DevPath, 1);
> + *el = (DevPath) {
> + .path = g_strdup(dev->canonical_path),
> + };
> + QAPI_LIST_PREPEND(*list, el);
> + }
> +
> + /* Recursively check all children */
> + object_child_foreach(obj, qdev_add_if_backend_transfer_supported, opaque);
> +
> + return 0;
> +}
> +
> +DevPathList *qmp_query_backend_transfer_support(Error **errp)
> +{
> + DevPathList *result = NULL;
> + Object *peripheral = machine_get_container("peripheral");
> +
> + object_child_foreach(peripheral, qdev_add_if_backend_transfer_supported,
> + &result);
> +
> + return result;
> +}
> +
> int qdev_sync_config(DeviceState *dev, Error **errp)
> {
> DeviceClass *dc = DEVICE_GET_CLASS(dev);
On 06.11.25 18:30, Markus Armbruster wrote: > Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> writes: > >> We are going to implement backend-transfer feature: some devices >> will be able to transfer their backend through migration stream >> for local migration through UNIX domain socket. For example, >> virtio-net will migrate its attached TAP netdev, with all its >> connected file descriptors. >> >> Let's add a command to list supporting devices (no one for now), >> together with necessary infrastructure in qdev code. > > Use case? Will add: With this command management tool can query such lists on source and target, and get intersection of them, to now the set of devices, for which we can enable backend-transfer for given source and target QEMUs. > >> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> >> --- >> include/hw/qdev-core.h | 7 +++++++ >> qapi/qdev.json | 26 +++++++++++++++++++++++++ >> system/qdev-monitor.c | 43 ++++++++++++++++++++++++++++++++++++++++++ >> 3 files changed, 76 insertions(+) >> >> diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h >> index 2caa0cbd26..0551fbaa6c 100644 -- Best regards, Vladimir
Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> writes: > On 06.11.25 18:30, Markus Armbruster wrote: >> Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> writes: >> >>> We are going to implement backend-transfer feature: some devices >>> will be able to transfer their backend through migration stream >>> for local migration through UNIX domain socket. For example, >>> virtio-net will migrate its attached TAP netdev, with all its >>> connected file descriptors. >>> >>> Let's add a command to list supporting devices (no one for now), >>> together with necessary infrastructure in qdev code. >> >> Use case? > > Will add: > > With this command management tool can query such lists on source and > target, and get intersection of them, to now the set of devices, for > which we can enable backend-transfer for given source and target QEMUs. I like it. Would it make sense to add something similar to QAPI schema doc comments? [...]
On 07.11.25 08:28, Markus Armbruster wrote: > Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> writes: > >> On 06.11.25 18:30, Markus Armbruster wrote: >>> Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> writes: >>> >>>> We are going to implement backend-transfer feature: some devices >>>> will be able to transfer their backend through migration stream >>>> for local migration through UNIX domain socket. For example, >>>> virtio-net will migrate its attached TAP netdev, with all its >>>> connected file descriptors. >>>> >>>> Let's add a command to list supporting devices (no one for now), >>>> together with necessary infrastructure in qdev code. >>> >>> Use case? >> >> Will add: >> >> With this command management tool can query such lists on source and >> target, and get intersection of them, to now the set of devices, for >> which we can enable backend-transfer for given source and target QEMUs. > > I like it. Would it make sense to add something similar to QAPI schema > doc comments? > Agree, will do. -- Best regards, Vladimir
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