Opt-out backend initialization code, and instead get the state
from migration channel (including inflight region).
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
---
hw/block/vhost-user-blk.c | 185 +++++++++++++++++++++++------
include/hw/virtio/vhost-user-blk.h | 2 +
migration/options.c | 7 ++
migration/options.h | 1 +
qapi/migration.json | 15 ++-
5 files changed, 169 insertions(+), 41 deletions(-)
diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
index c8bc2c78e6..2e6ef6477e 100644
--- a/hw/block/vhost-user-blk.c
+++ b/hw/block/vhost-user-blk.c
@@ -17,6 +17,7 @@
*/
#include "qemu/osdep.h"
+#include "qapi-types-run-state.h"
#include "qapi/error.h"
#include "qemu/error-report.h"
#include "qemu/cutils.h"
@@ -32,6 +33,11 @@
#include "system/system.h"
#include "system/runstate.h"
#include "trace.h"
+#include "migration/qemu-file.h"
+#include "migration/migration.h"
+#include "migration/options.h"
+#include "qemu/event_notifier.h"
+#include <sys/mman.h>
static const int user_feature_bits[] = {
VIRTIO_BLK_F_SIZE_MAX,
@@ -159,32 +165,35 @@ static int vhost_user_blk_start(VirtIODevice *vdev, Error **errp)
s->dev.acked_features = vdev->guest_features;
- ret = vhost_dev_prepare_inflight(&s->dev, vdev);
- if (ret < 0) {
- error_setg_errno(errp, -ret, "Error setting inflight format");
- goto err_guest_notifiers;
- }
-
- if (!s->inflight->addr) {
- ret = vhost_dev_get_inflight(&s->dev, s->queue_size, s->inflight);
+ if (!s->dev.migrating_backend) {
+ ret = vhost_dev_prepare_inflight(&s->dev, vdev);
if (ret < 0) {
- error_setg_errno(errp, -ret, "Error getting inflight");
+ error_setg_errno(errp, -ret, "Error setting inflight format");
goto err_guest_notifiers;
}
- }
- ret = vhost_dev_set_inflight(&s->dev, s->inflight);
- if (ret < 0) {
- error_setg_errno(errp, -ret, "Error setting inflight");
- goto err_guest_notifiers;
- }
+ if (!s->inflight->addr) {
+ ret = vhost_dev_get_inflight(&s->dev, s->queue_size, s->inflight);
+ if (ret < 0) {
+ error_setg_errno(errp, -ret, "Error getting inflight");
+ goto err_guest_notifiers;
+ }
+ }
- /* guest_notifier_mask/pending not used yet, so just unmask
- * everything here. virtio-pci will do the right thing by
- * enabling/disabling irqfd.
- */
- for (i = 0; i < s->dev.nvqs; i++) {
- vhost_virtqueue_mask(&s->dev, vdev, i, false);
+ ret = vhost_dev_set_inflight(&s->dev, s->inflight);
+ if (ret < 0) {
+ error_setg_errno(errp, -ret, "Error setting inflight");
+ goto err_guest_notifiers;
+ }
+
+ /*
+ * guest_notifier_mask/pending not used yet, so just unmask
+ * everything here. virtio-pci will do the right thing by
+ * enabling/disabling irqfd.
+ */
+ for (i = 0; i < s->dev.nvqs; i++) {
+ vhost_virtqueue_mask(&s->dev, vdev, i, false);
+ }
}
s->dev.vq_index_end = s->dev.nvqs;
@@ -231,6 +240,10 @@ static int vhost_user_blk_stop(VirtIODevice *vdev)
force_stop = s->skip_get_vring_base_on_force_shutdown &&
qemu_force_shutdown_requested();
+ s->dev.migrating_backend = s->dev.migrating_backend ||
+ (runstate_check(RUN_STATE_FINISH_MIGRATE) &&
+ migrate_local_vhost_user_blk());
+
ret = force_stop ? vhost_dev_force_stop(&s->dev, vdev, true) :
vhost_dev_stop(&s->dev, vdev, true);
@@ -343,7 +356,9 @@ static void vhost_user_blk_reset(VirtIODevice *vdev)
vhost_dev_free_inflight(s->inflight);
}
-static int vhost_user_blk_connect(DeviceState *dev, Error **errp)
+static int vhost_user_blk_connect(DeviceState *dev,
+ bool migrating_backend,
+ Error **errp)
{
VirtIODevice *vdev = VIRTIO_DEVICE(dev);
VHostUserBlk *s = VHOST_USER_BLK(vdev);
@@ -359,6 +374,7 @@ static int vhost_user_blk_connect(DeviceState *dev, Error **errp)
s->dev.nvqs = s->num_queues;
s->dev.vqs = s->vhost_vqs;
s->dev.vq_index = 0;
+ s->dev.migrating_backend = migrating_backend;
vhost_dev_set_config_notifier(&s->dev, &blk_ops);
@@ -409,7 +425,7 @@ static void vhost_user_blk_event(void *opaque, QEMUChrEvent event)
switch (event) {
case CHR_EVENT_OPENED:
- if (vhost_user_blk_connect(dev, &local_err) < 0) {
+ if (vhost_user_blk_connect(dev, false, &local_err) < 0) {
error_report_err(local_err);
qemu_chr_fe_disconnect(&s->chardev);
return;
@@ -428,31 +444,37 @@ static void vhost_user_blk_event(void *opaque, QEMUChrEvent event)
}
}
-static int vhost_user_blk_realize_connect(VHostUserBlk *s, Error **errp)
+static int vhost_user_blk_realize_connect(VHostUserBlk *s,
+ bool migrating_backend,
+ Error **errp)
{
DeviceState *dev = DEVICE(s);
int ret;
s->connected = false;
- ret = qemu_chr_fe_wait_connected(&s->chardev, errp);
- if (ret < 0) {
- return ret;
+ if (!migrating_backend) {
+ ret = qemu_chr_fe_wait_connected(&s->chardev, errp);
+ if (ret < 0) {
+ return ret;
+ }
}
- ret = vhost_user_blk_connect(dev, errp);
+ ret = vhost_user_blk_connect(dev, migrating_backend, errp);
if (ret < 0) {
qemu_chr_fe_disconnect(&s->chardev);
return ret;
}
assert(s->connected);
- ret = vhost_dev_get_config(&s->dev, (uint8_t *)&s->blkcfg,
- VIRTIO_DEVICE(s)->config_len, errp);
- if (ret < 0) {
- qemu_chr_fe_disconnect(&s->chardev);
- vhost_dev_cleanup(&s->dev);
- return ret;
+ if (!migrating_backend) {
+ ret = vhost_dev_get_config(&s->dev, (uint8_t *)&s->blkcfg,
+ VIRTIO_DEVICE(s)->config_len, errp);
+ if (ret < 0) {
+ qemu_chr_fe_disconnect(&s->chardev);
+ vhost_dev_cleanup(&s->dev);
+ return ret;
+ }
}
return 0;
@@ -469,6 +491,11 @@ static void vhost_user_blk_device_realize(DeviceState *dev, Error **errp)
trace_vhost_user_blk_device_realize();
+ if (s->incoming_backend && !runstate_check(RUN_STATE_INMIGRATE)) {
+ error_setg(errp, "__yc_local-incoming can be used "
+ "only for incoming migration");
+ }
+
if (!s->chardev.chr) {
error_setg(errp, "chardev is mandatory");
return;
@@ -517,7 +544,7 @@ static void vhost_user_blk_device_realize(DeviceState *dev, Error **errp)
error_report_err(*errp);
*errp = NULL;
}
- ret = vhost_user_blk_realize_connect(s, errp);
+ ret = vhost_user_blk_realize_connect(s, s->incoming_backend, errp);
} while (ret < 0 && retries--);
if (ret < 0) {
@@ -525,9 +552,12 @@ static void vhost_user_blk_device_realize(DeviceState *dev, Error **errp)
}
/* we're fully initialized, now we can operate, so add the handler */
- qemu_chr_fe_set_handlers(&s->chardev, NULL, NULL,
- vhost_user_blk_event, NULL, (void *)dev,
- NULL, true);
+ if (!s->incoming_backend) {
+ qemu_chr_fe_set_handlers(&s->chardev, NULL, NULL,
+ vhost_user_blk_event, NULL, (void *)dev,
+ NULL, true);
+ }
+
trace_vhost_user_blk_device_realize_finish();
return;
@@ -592,6 +622,79 @@ static const VMStateDescription vmstate_vhost_user_blk = {
},
};
+static void vhost_user_blk_save(VirtIODevice *vdev, QEMUFile *f)
+{
+ VHostUserBlk *s = VHOST_USER_BLK(vdev);
+ struct vhost_dev *hdev = vhost_user_blk_get_vhost(vdev);
+
+ if (!hdev->migrating_backend) {
+ return;
+ }
+
+ qemu_file_put_fd(f, s->inflight->fd);
+ qemu_put_be64(f, s->inflight->size);
+ qemu_put_be64(f, s->inflight->offset);
+ qemu_put_be16(f, s->inflight->queue_size);
+
+ vhost_save_backend(hdev, f);
+}
+
+static int vhost_user_blk_load(VirtIODevice *vdev, QEMUFile *f,
+ int version_id)
+{
+ VHostUserBlk *s = VHOST_USER_BLK(vdev);
+ struct vhost_dev *hdev = vhost_user_blk_get_vhost(vdev);
+
+ if (!hdev->migrating_backend) {
+ return 0;
+ }
+
+ s->inflight->fd = qemu_file_get_fd(f);
+ qemu_get_be64s(f, &s->inflight->size);
+ qemu_get_be64s(f, &s->inflight->offset);
+ qemu_get_be16s(f, &s->inflight->queue_size);
+
+ s->inflight->addr = mmap(0, s->inflight->size, PROT_READ | PROT_WRITE,
+ MAP_SHARED, s->inflight->fd, s->inflight->offset);
+ if (s->inflight->addr == MAP_FAILED) {
+ return -EINVAL;
+ }
+
+ vhost_load_backend(hdev, f);
+
+ return 0;
+}
+
+static int vhost_user_blk_post_load(VirtIODevice *vdev)
+{
+ VHostUserBlk *s = VHOST_USER_BLK(vdev);
+ struct vhost_dev *hdev = vhost_user_blk_get_vhost(vdev);
+ DeviceState *dev = &s->parent_obj.parent_obj;
+
+ if (!hdev->migrating_backend) {
+ return 0;
+ }
+
+ memcpy(&s->blkcfg, vdev->config, vdev->config_len);
+
+ /* we're fully initialized, now we can operate, so add the handler */
+ qemu_chr_fe_set_handlers(&s->chardev, NULL, NULL,
+ vhost_user_blk_event, NULL, (void *)dev,
+ NULL, true);
+
+ return 0;
+}
+
+static bool vhost_user_blk_skip_migration_log(VirtIODevice *vdev)
+{
+ /*
+ * Note that hdev->migrating_backend is false at this moment,
+ * as logging is being setup during outging migration setup stage,
+ * which is far before vm stop.
+ */
+ return migrate_local_vhost_user_blk();
+}
+
static const Property vhost_user_blk_properties[] = {
DEFINE_PROP_CHR("chardev", VHostUserBlk, chardev),
DEFINE_PROP_UINT16("num-queues", VHostUserBlk, num_queues,
@@ -605,6 +708,8 @@ static const Property vhost_user_blk_properties[] = {
VIRTIO_BLK_F_WRITE_ZEROES, true),
DEFINE_PROP_BOOL("skip-get-vring-base-on-force-shutdown", VHostUserBlk,
skip_get_vring_base_on_force_shutdown, false),
+ DEFINE_PROP_BOOL("local-incoming", VHostUserBlk,
+ incoming_backend, false),
};
static void vhost_user_blk_class_init(ObjectClass *klass, const void *data)
@@ -624,6 +729,10 @@ static void vhost_user_blk_class_init(ObjectClass *klass, const void *data)
vdc->set_status = vhost_user_blk_set_status;
vdc->reset = vhost_user_blk_reset;
vdc->get_vhost = vhost_user_blk_get_vhost;
+ vdc->save = vhost_user_blk_save;
+ vdc->load = vhost_user_blk_load;
+ vdc->post_load = vhost_user_blk_post_load,
+ vdc->skip_vhost_migration_log = vhost_user_blk_skip_migration_log;
}
static const TypeInfo vhost_user_blk_info = {
diff --git a/include/hw/virtio/vhost-user-blk.h b/include/hw/virtio/vhost-user-blk.h
index a10f785672..b06f55fd6f 100644
--- a/include/hw/virtio/vhost-user-blk.h
+++ b/include/hw/virtio/vhost-user-blk.h
@@ -52,6 +52,8 @@ struct VHostUserBlk {
bool started_vu;
bool skip_get_vring_base_on_force_shutdown;
+
+ bool incoming_backend;
};
#endif
diff --git a/migration/options.c b/migration/options.c
index dffb6910f4..11b719c81b 100644
--- a/migration/options.c
+++ b/migration/options.c
@@ -269,6 +269,13 @@ bool migrate_local_char_socket(void)
return s->capabilities[MIGRATION_CAPABILITY_LOCAL_CHAR_SOCKET];
}
+bool migrate_local_vhost_user_blk(void)
+{
+ MigrationState *s = migrate_get_current();
+
+ return s->capabilities[MIGRATION_CAPABILITY_LOCAL_VHOST_USER_BLK];
+}
+
bool migrate_ignore_shared(void)
{
MigrationState *s = migrate_get_current();
diff --git a/migration/options.h b/migration/options.h
index 40971f0aa0..5a40ac073d 100644
--- a/migration/options.h
+++ b/migration/options.h
@@ -31,6 +31,7 @@ bool migrate_dirty_bitmaps(void);
bool migrate_events(void);
bool migrate_mapped_ram(void);
bool migrate_local_char_socket(void);
+bool migrate_local_vhost_user_blk(void);
bool migrate_ignore_shared(void);
bool migrate_late_block_activate(void);
bool migrate_multifd(void);
diff --git a/qapi/migration.json b/qapi/migration.json
index 4f282d168e..ead7f4d17c 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -520,11 +520,19 @@
# @local-char-socket: Migrate socket chardevs open file descriptors.
# Only may be used when migration channel is unix socket. Only
# involves socket chardevs with "support-local-migration" option
-# enabled. (since 10.2)
+# enabled. For target device also @local-incoming option must
+# be specified (since 10.2)
+#
+# @local-vhost-user-blk: Migrate vhost-user-blk locally, keeping
+# backend alive. Open file descriptors and backend-related state are
+# migrated. Only may be used when migration channel is unix socket.
+# For target device also @local-incoming option must be specified
+# (since 10.2)
#
# Features:
#
-# @unstable: Members @x-colo and @x-ignore-shared are experimental.
+# @unstable: Members @x-colo, @x-ignore-shared, @local-char-socket,
+# @local-vhost-user-blk are experimental.
# @deprecated: Member @zero-blocks is deprecated as being part of
# block migration which was already removed.
#
@@ -542,7 +550,8 @@
'validate-uuid', 'background-snapshot',
'zero-copy-send', 'postcopy-preempt', 'switchover-ack',
'dirty-limit', 'mapped-ram',
- { 'name': 'local-char-socket', 'features': [ 'unstable' ] } ] }
+ { 'name': 'local-char-socket', 'features': [ 'unstable' ] },
+ { 'name': 'local-vhost-user-blk', 'features': [ 'unstable' ] } ] }
##
# @MigrationCapabilityStatus:
--
2.48.1A small question here but will review more thoroughly pending feedback
on my overall comments.
On Wed, Aug 13, 2025 at 12:53 PM Vladimir Sementsov-Ogievskiy
<vsementsov@yandex-team.ru> wrote:
>
> Opt-out backend initialization code, and instead get the state
> from migration channel (including inflight region).
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
> ---
> hw/block/vhost-user-blk.c | 185 +++++++++++++++++++++++------
> include/hw/virtio/vhost-user-blk.h | 2 +
> migration/options.c | 7 ++
> migration/options.h | 1 +
> qapi/migration.json | 15 ++-
> 5 files changed, 169 insertions(+), 41 deletions(-)
>
> diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
> index c8bc2c78e6..2e6ef6477e 100644
> --- a/hw/block/vhost-user-blk.c
> +++ b/hw/block/vhost-user-blk.c
> @@ -17,6 +17,7 @@
> */
>
> #include "qemu/osdep.h"
> +#include "qapi-types-run-state.h"
> #include "qapi/error.h"
> #include "qemu/error-report.h"
> #include "qemu/cutils.h"
> @@ -32,6 +33,11 @@
> #include "system/system.h"
> #include "system/runstate.h"
> #include "trace.h"
> +#include "migration/qemu-file.h"
> +#include "migration/migration.h"
> +#include "migration/options.h"
> +#include "qemu/event_notifier.h"
> +#include <sys/mman.h>
>
> static const int user_feature_bits[] = {
> VIRTIO_BLK_F_SIZE_MAX,
> @@ -159,32 +165,35 @@ static int vhost_user_blk_start(VirtIODevice *vdev, Error **errp)
>
> s->dev.acked_features = vdev->guest_features;
>
> - ret = vhost_dev_prepare_inflight(&s->dev, vdev);
> - if (ret < 0) {
> - error_setg_errno(errp, -ret, "Error setting inflight format");
> - goto err_guest_notifiers;
> - }
> -
> - if (!s->inflight->addr) {
> - ret = vhost_dev_get_inflight(&s->dev, s->queue_size, s->inflight);
> + if (!s->dev.migrating_backend) {
> + ret = vhost_dev_prepare_inflight(&s->dev, vdev);
> if (ret < 0) {
> - error_setg_errno(errp, -ret, "Error getting inflight");
> + error_setg_errno(errp, -ret, "Error setting inflight format");
> goto err_guest_notifiers;
> }
> - }
>
> - ret = vhost_dev_set_inflight(&s->dev, s->inflight);
> - if (ret < 0) {
> - error_setg_errno(errp, -ret, "Error setting inflight");
> - goto err_guest_notifiers;
> - }
> + if (!s->inflight->addr) {
> + ret = vhost_dev_get_inflight(&s->dev, s->queue_size, s->inflight);
> + if (ret < 0) {
> + error_setg_errno(errp, -ret, "Error getting inflight");
> + goto err_guest_notifiers;
> + }
> + }
>
> - /* guest_notifier_mask/pending not used yet, so just unmask
> - * everything here. virtio-pci will do the right thing by
> - * enabling/disabling irqfd.
> - */
> - for (i = 0; i < s->dev.nvqs; i++) {
> - vhost_virtqueue_mask(&s->dev, vdev, i, false);
> + ret = vhost_dev_set_inflight(&s->dev, s->inflight);
> + if (ret < 0) {
> + error_setg_errno(errp, -ret, "Error setting inflight");
> + goto err_guest_notifiers;
> + }
> +
> + /*
> + * guest_notifier_mask/pending not used yet, so just unmask
> + * everything here. virtio-pci will do the right thing by
> + * enabling/disabling irqfd.
> + */
> + for (i = 0; i < s->dev.nvqs; i++) {
> + vhost_virtqueue_mask(&s->dev, vdev, i, false);
> + }
> }
>
> s->dev.vq_index_end = s->dev.nvqs;
> @@ -231,6 +240,10 @@ static int vhost_user_blk_stop(VirtIODevice *vdev)
> force_stop = s->skip_get_vring_base_on_force_shutdown &&
> qemu_force_shutdown_requested();
>
> + s->dev.migrating_backend = s->dev.migrating_backend ||
> + (runstate_check(RUN_STATE_FINISH_MIGRATE) &&
> + migrate_local_vhost_user_blk());
> +
> ret = force_stop ? vhost_dev_force_stop(&s->dev, vdev, true) :
> vhost_dev_stop(&s->dev, vdev, true);
>
> @@ -343,7 +356,9 @@ static void vhost_user_blk_reset(VirtIODevice *vdev)
> vhost_dev_free_inflight(s->inflight);
> }
>
> -static int vhost_user_blk_connect(DeviceState *dev, Error **errp)
> +static int vhost_user_blk_connect(DeviceState *dev,
> + bool migrating_backend,
> + Error **errp)
> {
> VirtIODevice *vdev = VIRTIO_DEVICE(dev);
> VHostUserBlk *s = VHOST_USER_BLK(vdev);
> @@ -359,6 +374,7 @@ static int vhost_user_blk_connect(DeviceState *dev, Error **errp)
> s->dev.nvqs = s->num_queues;
> s->dev.vqs = s->vhost_vqs;
> s->dev.vq_index = 0;
> + s->dev.migrating_backend = migrating_backend;
>
> vhost_dev_set_config_notifier(&s->dev, &blk_ops);
>
> @@ -409,7 +425,7 @@ static void vhost_user_blk_event(void *opaque, QEMUChrEvent event)
>
> switch (event) {
> case CHR_EVENT_OPENED:
> - if (vhost_user_blk_connect(dev, &local_err) < 0) {
> + if (vhost_user_blk_connect(dev, false, &local_err) < 0) {
> error_report_err(local_err);
> qemu_chr_fe_disconnect(&s->chardev);
> return;
> @@ -428,31 +444,37 @@ static void vhost_user_blk_event(void *opaque, QEMUChrEvent event)
> }
> }
>
> -static int vhost_user_blk_realize_connect(VHostUserBlk *s, Error **errp)
> +static int vhost_user_blk_realize_connect(VHostUserBlk *s,
> + bool migrating_backend,
> + Error **errp)
> {
> DeviceState *dev = DEVICE(s);
> int ret;
>
> s->connected = false;
>
> - ret = qemu_chr_fe_wait_connected(&s->chardev, errp);
> - if (ret < 0) {
> - return ret;
> + if (!migrating_backend) {
> + ret = qemu_chr_fe_wait_connected(&s->chardev, errp);
> + if (ret < 0) {
> + return ret;
> + }
> }
>
> - ret = vhost_user_blk_connect(dev, errp);
> + ret = vhost_user_blk_connect(dev, migrating_backend, errp);
> if (ret < 0) {
> qemu_chr_fe_disconnect(&s->chardev);
> return ret;
> }
> assert(s->connected);
>
> - ret = vhost_dev_get_config(&s->dev, (uint8_t *)&s->blkcfg,
> - VIRTIO_DEVICE(s)->config_len, errp);
> - if (ret < 0) {
> - qemu_chr_fe_disconnect(&s->chardev);
> - vhost_dev_cleanup(&s->dev);
> - return ret;
> + if (!migrating_backend) {
> + ret = vhost_dev_get_config(&s->dev, (uint8_t *)&s->blkcfg,
> + VIRTIO_DEVICE(s)->config_len, errp);
> + if (ret < 0) {
> + qemu_chr_fe_disconnect(&s->chardev);
> + vhost_dev_cleanup(&s->dev);
> + return ret;
> + }
> }
>
> return 0;
> @@ -469,6 +491,11 @@ static void vhost_user_blk_device_realize(DeviceState *dev, Error **errp)
>
> trace_vhost_user_blk_device_realize();
>
> + if (s->incoming_backend && !runstate_check(RUN_STATE_INMIGRATE)) {
> + error_setg(errp, "__yc_local-incoming can be used "
> + "only for incoming migration");
> + }
> +
> if (!s->chardev.chr) {
> error_setg(errp, "chardev is mandatory");
> return;
> @@ -517,7 +544,7 @@ static void vhost_user_blk_device_realize(DeviceState *dev, Error **errp)
> error_report_err(*errp);
> *errp = NULL;
> }
> - ret = vhost_user_blk_realize_connect(s, errp);
> + ret = vhost_user_blk_realize_connect(s, s->incoming_backend, errp);
> } while (ret < 0 && retries--);
>
> if (ret < 0) {
> @@ -525,9 +552,12 @@ static void vhost_user_blk_device_realize(DeviceState *dev, Error **errp)
> }
>
> /* we're fully initialized, now we can operate, so add the handler */
> - qemu_chr_fe_set_handlers(&s->chardev, NULL, NULL,
> - vhost_user_blk_event, NULL, (void *)dev,
> - NULL, true);
> + if (!s->incoming_backend) {
> + qemu_chr_fe_set_handlers(&s->chardev, NULL, NULL,
> + vhost_user_blk_event, NULL, (void *)dev,
> + NULL, true);
> + }
> +
> trace_vhost_user_blk_device_realize_finish();
> return;
>
> @@ -592,6 +622,79 @@ static const VMStateDescription vmstate_vhost_user_blk = {
> },
> };
>
> +static void vhost_user_blk_save(VirtIODevice *vdev, QEMUFile *f)
> +{
> + VHostUserBlk *s = VHOST_USER_BLK(vdev);
> + struct vhost_dev *hdev = vhost_user_blk_get_vhost(vdev);
> +
> + if (!hdev->migrating_backend) {
> + return;
> + }
> +
> + qemu_file_put_fd(f, s->inflight->fd);
> + qemu_put_be64(f, s->inflight->size);
> + qemu_put_be64(f, s->inflight->offset);
> + qemu_put_be16(f, s->inflight->queue_size);
> +
> + vhost_save_backend(hdev, f);
> +}
> +
> +static int vhost_user_blk_load(VirtIODevice *vdev, QEMUFile *f,
> + int version_id)
> +{
> + VHostUserBlk *s = VHOST_USER_BLK(vdev);
> + struct vhost_dev *hdev = vhost_user_blk_get_vhost(vdev);
> +
> + if (!hdev->migrating_backend) {
> + return 0;
> + }
> +
> + s->inflight->fd = qemu_file_get_fd(f);
> + qemu_get_be64s(f, &s->inflight->size);
> + qemu_get_be64s(f, &s->inflight->offset);
> + qemu_get_be16s(f, &s->inflight->queue_size);
> +
> + s->inflight->addr = mmap(0, s->inflight->size, PROT_READ | PROT_WRITE,
> + MAP_SHARED, s->inflight->fd, s->inflight->offset);
> + if (s->inflight->addr == MAP_FAILED) {
> + return -EINVAL;
> + }
> +
> + vhost_load_backend(hdev, f);
> +
> + return 0;
> +}
> +
> +static int vhost_user_blk_post_load(VirtIODevice *vdev)
> +{
> + VHostUserBlk *s = VHOST_USER_BLK(vdev);
> + struct vhost_dev *hdev = vhost_user_blk_get_vhost(vdev);
> + DeviceState *dev = &s->parent_obj.parent_obj;
> +
> + if (!hdev->migrating_backend) {
> + return 0;
> + }
> +
> + memcpy(&s->blkcfg, vdev->config, vdev->config_len);
> +
> + /* we're fully initialized, now we can operate, so add the handler */
> + qemu_chr_fe_set_handlers(&s->chardev, NULL, NULL,
> + vhost_user_blk_event, NULL, (void *)dev,
> + NULL, true);
> +
> + return 0;
> +}
> +
> +static bool vhost_user_blk_skip_migration_log(VirtIODevice *vdev)
> +{
> + /*
> + * Note that hdev->migrating_backend is false at this moment,
> + * as logging is being setup during outging migration setup stage,
> + * which is far before vm stop.
> + */
> + return migrate_local_vhost_user_blk();
> +}
> +
> static const Property vhost_user_blk_properties[] = {
> DEFINE_PROP_CHR("chardev", VHostUserBlk, chardev),
> DEFINE_PROP_UINT16("num-queues", VHostUserBlk, num_queues,
> @@ -605,6 +708,8 @@ static const Property vhost_user_blk_properties[] = {
> VIRTIO_BLK_F_WRITE_ZEROES, true),
> DEFINE_PROP_BOOL("skip-get-vring-base-on-force-shutdown", VHostUserBlk,
> skip_get_vring_base_on_force_shutdown, false),
> + DEFINE_PROP_BOOL("local-incoming", VHostUserBlk,
> + incoming_backend, false),
> };
>
> static void vhost_user_blk_class_init(ObjectClass *klass, const void *data)
> @@ -624,6 +729,10 @@ static void vhost_user_blk_class_init(ObjectClass *klass, const void *data)
> vdc->set_status = vhost_user_blk_set_status;
> vdc->reset = vhost_user_blk_reset;
> vdc->get_vhost = vhost_user_blk_get_vhost;
> + vdc->save = vhost_user_blk_save;
> + vdc->load = vhost_user_blk_load;
> + vdc->post_load = vhost_user_blk_post_load,
> + vdc->skip_vhost_migration_log = vhost_user_blk_skip_migration_log;
> }
>
> static const TypeInfo vhost_user_blk_info = {
> diff --git a/include/hw/virtio/vhost-user-blk.h b/include/hw/virtio/vhost-user-blk.h
> index a10f785672..b06f55fd6f 100644
> --- a/include/hw/virtio/vhost-user-blk.h
> +++ b/include/hw/virtio/vhost-user-blk.h
> @@ -52,6 +52,8 @@ struct VHostUserBlk {
> bool started_vu;
>
> bool skip_get_vring_base_on_force_shutdown;
> +
> + bool incoming_backend;
> };
>
> #endif
> diff --git a/migration/options.c b/migration/options.c
> index dffb6910f4..11b719c81b 100644
> --- a/migration/options.c
> +++ b/migration/options.c
> @@ -269,6 +269,13 @@ bool migrate_local_char_socket(void)
> return s->capabilities[MIGRATION_CAPABILITY_LOCAL_CHAR_SOCKET];
> }
>
> +bool migrate_local_vhost_user_blk(void)
> +{
> + MigrationState *s = migrate_get_current();
> +
Where was MIGRATION_CAPABILITY_LOCAL_VHOST_USER_BLK added/defined?
> + return s->capabilities[MIGRATION_CAPABILITY_LOCAL_VHOST_USER_BLK];
> +}
> +
> bool migrate_ignore_shared(void)
> {
> MigrationState *s = migrate_get_current();
> diff --git a/migration/options.h b/migration/options.h
> index 40971f0aa0..5a40ac073d 100644
> --- a/migration/options.h
> +++ b/migration/options.h
> @@ -31,6 +31,7 @@ bool migrate_dirty_bitmaps(void);
> bool migrate_events(void);
> bool migrate_mapped_ram(void);
> bool migrate_local_char_socket(void);
> +bool migrate_local_vhost_user_blk(void);
> bool migrate_ignore_shared(void);
> bool migrate_late_block_activate(void);
> bool migrate_multifd(void);
> diff --git a/qapi/migration.json b/qapi/migration.json
> index 4f282d168e..ead7f4d17c 100644
> --- a/qapi/migration.json
> +++ b/qapi/migration.json
> @@ -520,11 +520,19 @@
> # @local-char-socket: Migrate socket chardevs open file descriptors.
> # Only may be used when migration channel is unix socket. Only
> # involves socket chardevs with "support-local-migration" option
> -# enabled. (since 10.2)
> +# enabled. For target device also @local-incoming option must
> +# be specified (since 10.2)
> +#
> +# @local-vhost-user-blk: Migrate vhost-user-blk locally, keeping
> +# backend alive. Open file descriptors and backend-related state are
> +# migrated. Only may be used when migration channel is unix socket.
> +# For target device also @local-incoming option must be specified
> +# (since 10.2)
> #
> # Features:
> #
> -# @unstable: Members @x-colo and @x-ignore-shared are experimental.
> +# @unstable: Members @x-colo, @x-ignore-shared, @local-char-socket,
> +# @local-vhost-user-blk are experimental.
> # @deprecated: Member @zero-blocks is deprecated as being part of
> # block migration which was already removed.
> #
> @@ -542,7 +550,8 @@
> 'validate-uuid', 'background-snapshot',
> 'zero-copy-send', 'postcopy-preempt', 'switchover-ack',
> 'dirty-limit', 'mapped-ram',
> - { 'name': 'local-char-socket', 'features': [ 'unstable' ] } ] }
> + { 'name': 'local-char-socket', 'features': [ 'unstable' ] },
> + { 'name': 'local-vhost-user-blk', 'features': [ 'unstable' ] } ] }
>
> ##
> # @MigrationCapabilityStatus:
> --
> 2.48.1
>
>
On 09.10.25 22:09, Raphael Norwitz wrote:
> A small question here but will review more thoroughly pending feedback
> on my overall comments.
>
I really hope you didn't spent much time on these 28-31 patches :/
> On Wed, Aug 13, 2025 at 12:53 PM Vladimir Sementsov-Ogievskiy
> <vsementsov@yandex-team.ru> wrote:
>>
[..]
>> --- a/migration/options.c
>> +++ b/migration/options.c
>> @@ -269,6 +269,13 @@ bool migrate_local_char_socket(void)
>> return s->capabilities[MIGRATION_CAPABILITY_LOCAL_CHAR_SOCKET];
>> }
>>
>> +bool migrate_local_vhost_user_blk(void)
>> +{
>> + MigrationState *s = migrate_get_current();
>> +
>
> Where was MIGRATION_CAPABILITY_LOCAL_VHOST_USER_BLK added/defined?
It is generated by QAPI code generator.
Exactly, it's defined by 'local-vhost-user-blk' member inside 'MigrationCapability':
{ 'enum': 'MigrationCapability',
'data': ['xbzrle', 'rdma-pin-all', 'auto-converge',
...
{ 'name': 'local-vhost-user-blk', 'features': [ 'unstable' ] } ] }
and after build, the generated code is in build/qapi/qapi-types-migration.h, as a enum:
typedef enum MigrationCapability {
MIGRATION_CAPABILITY_XBZRLE,
,,,
MIGRATION_CAPABILITY_LOCAL_VHOST_USER_BLK,
MIGRATION_CAPABILITY__MAX,
} MigrationCapability;
In v2, I'll follow the interface of virtio-net series, look at
https://patchew.org/QEMU/20250923100110.70862-1-vsementsov@yandex-team.ru/20250923100110.70862-17-vsementsov@yandex-team.ru/
so, it would be migration parameter instead of capability, like
QMP migrate-set-parameters {... backend-transfer = ["vhost-user-blk"] }
and to enable both vhost-user-blk and virtio-net-tap together:
QMP migrate-set-parameters {... backend-transfer = ["vhost-user-blk", "virtio-net-tap"] }
>
>
>> + return s->capabilities[MIGRATION_CAPABILITY_LOCAL_VHOST_USER_BLK];
>> +}
>> +
[..]
--
Best regards,
Vladimir
On Thu, Oct 9, 2025 at 5:14 PM Vladimir Sementsov-Ogievskiy
<vsementsov@yandex-team.ru> wrote:
>
> On 09.10.25 22:09, Raphael Norwitz wrote:
> > A small question here but will review more thoroughly pending feedback
> > on my overall comments.
> >
>
> I really hope you didn't spent much time on these 28-31 patches :/
>
I spent much more time on the cleanups :)
> > On Wed, Aug 13, 2025 at 12:53 PM Vladimir Sementsov-Ogievskiy
> > <vsementsov@yandex-team.ru> wrote:
> >>
>
> [..]
>
> >> --- a/migration/options.c
> >> +++ b/migration/options.c
> >> @@ -269,6 +269,13 @@ bool migrate_local_char_socket(void)
> >> return s->capabilities[MIGRATION_CAPABILITY_LOCAL_CHAR_SOCKET];
> >> }
> >>
> >> +bool migrate_local_vhost_user_blk(void)
> >> +{
> >> + MigrationState *s = migrate_get_current();
> >> +
> >
> > Where was MIGRATION_CAPABILITY_LOCAL_VHOST_USER_BLK added/defined?
>
> It is generated by QAPI code generator.
>
> Exactly, it's defined by 'local-vhost-user-blk' member inside 'MigrationCapability':
>
> { 'enum': 'MigrationCapability',
> 'data': ['xbzrle', 'rdma-pin-all', 'auto-converge',
>
> ...
>
> { 'name': 'local-vhost-user-blk', 'features': [ 'unstable' ] } ] }
>
>
> and after build, the generated code is in build/qapi/qapi-types-migration.h, as a enum:
>
> typedef enum MigrationCapability {
> MIGRATION_CAPABILITY_XBZRLE,
>
> ,,,
>
> MIGRATION_CAPABILITY_LOCAL_VHOST_USER_BLK,
> MIGRATION_CAPABILITY__MAX,
> } MigrationCapability;
>
>
> In v2, I'll follow the interface of virtio-net series, look at
>
> https://patchew.org/QEMU/20250923100110.70862-1-vsementsov@yandex-team.ru/20250923100110.70862-17-vsementsov@yandex-team.ru/
>
> so, it would be migration parameter instead of capability, like
>
> QMP migrate-set-parameters {... backend-transfer = ["vhost-user-blk"] }
>
> and to enable both vhost-user-blk and virtio-net-tap together:
>
> QMP migrate-set-parameters {... backend-transfer = ["vhost-user-blk", "virtio-net-tap"] }
>
Why do we need two separate migration parameters for vhost-user-blk
and virtio-net-tap? Why not have a single parameter for virtio local
migrations and, if it is set, all backends types which support local
migration can advertise and take advantage of it?
> >
> >
> >> + return s->capabilities[MIGRATION_CAPABILITY_LOCAL_VHOST_USER_BLK];
> >> +}
> >> +
>
> [..]
>
>
> --
> Best regards,
> Vladimir
On 10.10.25 02:43, Raphael Norwitz wrote:
> On Thu, Oct 9, 2025 at 5:14 PM Vladimir Sementsov-Ogievskiy
> <vsementsov@yandex-team.ru> wrote:
>>
>> On 09.10.25 22:09, Raphael Norwitz wrote:
>>> A small question here but will review more thoroughly pending feedback
>>> on my overall comments.
>>>
>>
>> I really hope you didn't spent much time on these 28-31 patches :/
>>
>
> I spent much more time on the cleanups :)
>
>>> On Wed, Aug 13, 2025 at 12:53 PM Vladimir Sementsov-Ogievskiy
>>> <vsementsov@yandex-team.ru> wrote:
>>>>
>>
>> [..]
>>
>>>> --- a/migration/options.c
>>>> +++ b/migration/options.c
>>>> @@ -269,6 +269,13 @@ bool migrate_local_char_socket(void)
>>>> return s->capabilities[MIGRATION_CAPABILITY_LOCAL_CHAR_SOCKET];
>>>> }
>>>>
>>>> +bool migrate_local_vhost_user_blk(void)
>>>> +{
>>>> + MigrationState *s = migrate_get_current();
>>>> +
>>>
>>> Where was MIGRATION_CAPABILITY_LOCAL_VHOST_USER_BLK added/defined?
>>
>> It is generated by QAPI code generator.
>>
>> Exactly, it's defined by 'local-vhost-user-blk' member inside 'MigrationCapability':
>>
>> { 'enum': 'MigrationCapability',
>> 'data': ['xbzrle', 'rdma-pin-all', 'auto-converge',
>>
>> ...
>>
>> { 'name': 'local-vhost-user-blk', 'features': [ 'unstable' ] } ] }
>>
>>
>> and after build, the generated code is in build/qapi/qapi-types-migration.h, as a enum:
>>
>> typedef enum MigrationCapability {
>> MIGRATION_CAPABILITY_XBZRLE,
>>
>> ,,,
>>
>> MIGRATION_CAPABILITY_LOCAL_VHOST_USER_BLK,
>> MIGRATION_CAPABILITY__MAX,
>> } MigrationCapability;
>>
>>
>> In v2, I'll follow the interface of virtio-net series, look at
>>
>> https://patchew.org/QEMU/20250923100110.70862-1-vsementsov@yandex-team.ru/20250923100110.70862-17-vsementsov@yandex-team.ru/
>>
>> so, it would be migration parameter instead of capability, like
>>
>> QMP migrate-set-parameters {... backend-transfer = ["vhost-user-blk"] }
>>
>> and to enable both vhost-user-blk and virtio-net-tap together:
>>
>> QMP migrate-set-parameters {... backend-transfer = ["vhost-user-blk", "virtio-net-tap"] }
>>
>
> Why do we need two separate migration parameters for vhost-user-blk
> and virtio-net-tap? Why not have a single parameter for virtio local
> migrations and, if it is set, all backends types which support local
> migration can advertise and take advantage of it?
As I describe in the commit message https://patchew.org/QEMU/20250923100110.70862-1-vsementsov@yandex-team.ru/20250923100110.70862-17-vsementsov@yandex-team.ru/ :
Why not simple boolean? To simplify migration to further versions,
when more devices will support backend-transfer migration.
Alternatively, we may add per-device option to disable backend-transfer
migration, but still:
1. It's more comfortable to set same capabilities/parameters on both
source and target QEMU, than care about each device.
2. To not break the design, that machine-type + device options +
migration capabilities and parameters are fully define the resulting
migration stream. We'll break this if add in future more
backend-transfer support in devices under same backend-transfer=true
parameter.
>
>>>
>>>
>>>> + return s->capabilities[MIGRATION_CAPABILITY_LOCAL_VHOST_USER_BLK];
>>>> +}
>>>> +
>>
>> [..]
>>
>>
>> --
>> Best regards,
>> Vladimir
--
Best regards,
Vladimir
On Fri, Oct 10, 2025 at 2:27 AM Vladimir Sementsov-Ogievskiy
<vsementsov@yandex-team.ru> wrote:
>
> On 10.10.25 02:43, Raphael Norwitz wrote:
> > On Thu, Oct 9, 2025 at 5:14 PM Vladimir Sementsov-Ogievskiy
> > <vsementsov@yandex-team.ru> wrote:
> >>
> >> On 09.10.25 22:09, Raphael Norwitz wrote:
> >>> A small question here but will review more thoroughly pending feedback
> >>> on my overall comments.
> >>>
> >>
> >> I really hope you didn't spent much time on these 28-31 patches :/
> >>
> >
> > I spent much more time on the cleanups :)
> >
> >>> On Wed, Aug 13, 2025 at 12:53 PM Vladimir Sementsov-Ogievskiy
> >>> <vsementsov@yandex-team.ru> wrote:
> >>>>
> >>
> >> [..]
> >>
> >>>> --- a/migration/options.c
> >>>> +++ b/migration/options.c
> >>>> @@ -269,6 +269,13 @@ bool migrate_local_char_socket(void)
> >>>> return s->capabilities[MIGRATION_CAPABILITY_LOCAL_CHAR_SOCKET];
> >>>> }
> >>>>
> >>>> +bool migrate_local_vhost_user_blk(void)
> >>>> +{
> >>>> + MigrationState *s = migrate_get_current();
> >>>> +
> >>>
> >>> Where was MIGRATION_CAPABILITY_LOCAL_VHOST_USER_BLK added/defined?
> >>
> >> It is generated by QAPI code generator.
> >>
> >> Exactly, it's defined by 'local-vhost-user-blk' member inside 'MigrationCapability':
> >>
> >> { 'enum': 'MigrationCapability',
> >> 'data': ['xbzrle', 'rdma-pin-all', 'auto-converge',
> >>
> >> ...
> >>
> >> { 'name': 'local-vhost-user-blk', 'features': [ 'unstable' ] } ] }
> >>
> >>
> >> and after build, the generated code is in build/qapi/qapi-types-migration.h, as a enum:
> >>
> >> typedef enum MigrationCapability {
> >> MIGRATION_CAPABILITY_XBZRLE,
> >>
> >> ,,,
> >>
> >> MIGRATION_CAPABILITY_LOCAL_VHOST_USER_BLK,
> >> MIGRATION_CAPABILITY__MAX,
> >> } MigrationCapability;
> >>
> >>
> >> In v2, I'll follow the interface of virtio-net series, look at
> >>
> >> https://patchew.org/QEMU/20250923100110.70862-1-vsementsov@yandex-team.ru/20250923100110.70862-17-vsementsov@yandex-team.ru/
> >>
> >> so, it would be migration parameter instead of capability, like
> >>
> >> QMP migrate-set-parameters {... backend-transfer = ["vhost-user-blk"] }
> >>
> >> and to enable both vhost-user-blk and virtio-net-tap together:
> >>
> >> QMP migrate-set-parameters {... backend-transfer = ["vhost-user-blk", "virtio-net-tap"] }
> >>
> >
> > Why do we need two separate migration parameters for vhost-user-blk
> > and virtio-net-tap? Why not have a single parameter for virtio local
> > migrations and, if it is set, all backends types which support local
> > migration can advertise and take advantage of it?
>
> As I describe in the commit message https://patchew.org/QEMU/20250923100110.70862-1-vsementsov@yandex-team.ru/20250923100110.70862-17-vsementsov@yandex-team.ru/ :
>
>
> Why not simple boolean? To simplify migration to further versions,
> when more devices will support backend-transfer migration.
>
> Alternatively, we may add per-device option to disable backend-transfer
> migration, but still:
>
> 1. It's more comfortable to set same capabilities/parameters on both
> source and target QEMU, than care about each device.
>
> 2. To not break the design, that machine-type + device options +
> migration capabilities and parameters are fully define the resulting
> migration stream. We'll break this if add in future more
> backend-transfer support in devices under same backend-transfer=true
> parameter.
ACK on needing a separate migration parameter. Thanks for the references.
I would suggest having the incoming_backend field in the struct
vhost_user (or maybe even in struct vhost_dev if the tap device
migration is similar enough) rather than in struct VHostUserBlk, so
that device-specific code can be kept as similar as possible.
>
>
> >
> >>>
> >>>
> >>>> + return s->capabilities[MIGRATION_CAPABILITY_LOCAL_VHOST_USER_BLK];
> >>>> +}
> >>>> +
> >>
> >> [..]
> >>
> >>
> >> --
> >> Best regards,
> >> Vladimir
>
>
> --
> Best regards,
> Vladimir
On 14.10.25 00:50, Raphael Norwitz wrote:
> On Fri, Oct 10, 2025 at 2:27 AM Vladimir Sementsov-Ogievskiy
> <vsementsov@yandex-team.ru> wrote:
>>
>> On 10.10.25 02:43, Raphael Norwitz wrote:
>>> On Thu, Oct 9, 2025 at 5:14 PM Vladimir Sementsov-Ogievskiy
>>> <vsementsov@yandex-team.ru> wrote:
>>>>
>>>> On 09.10.25 22:09, Raphael Norwitz wrote:
>>>>> A small question here but will review more thoroughly pending feedback
>>>>> on my overall comments.
>>>>>
>>>>
>>>> I really hope you didn't spent much time on these 28-31 patches :/
>>>>
>>>
>>> I spent much more time on the cleanups :)
>>>
>>>>> On Wed, Aug 13, 2025 at 12:53 PM Vladimir Sementsov-Ogievskiy
>>>>> <vsementsov@yandex-team.ru> wrote:
>>>>>>
>>>>
>>>> [..]
>>>>
>>>>>> --- a/migration/options.c
>>>>>> +++ b/migration/options.c
>>>>>> @@ -269,6 +269,13 @@ bool migrate_local_char_socket(void)
>>>>>> return s->capabilities[MIGRATION_CAPABILITY_LOCAL_CHAR_SOCKET];
>>>>>> }
>>>>>>
>>>>>> +bool migrate_local_vhost_user_blk(void)
>>>>>> +{
>>>>>> + MigrationState *s = migrate_get_current();
>>>>>> +
>>>>>
>>>>> Where was MIGRATION_CAPABILITY_LOCAL_VHOST_USER_BLK added/defined?
>>>>
>>>> It is generated by QAPI code generator.
>>>>
>>>> Exactly, it's defined by 'local-vhost-user-blk' member inside 'MigrationCapability':
>>>>
>>>> { 'enum': 'MigrationCapability',
>>>> 'data': ['xbzrle', 'rdma-pin-all', 'auto-converge',
>>>>
>>>> ...
>>>>
>>>> { 'name': 'local-vhost-user-blk', 'features': [ 'unstable' ] } ] }
>>>>
>>>>
>>>> and after build, the generated code is in build/qapi/qapi-types-migration.h, as a enum:
>>>>
>>>> typedef enum MigrationCapability {
>>>> MIGRATION_CAPABILITY_XBZRLE,
>>>>
>>>> ,,,
>>>>
>>>> MIGRATION_CAPABILITY_LOCAL_VHOST_USER_BLK,
>>>> MIGRATION_CAPABILITY__MAX,
>>>> } MigrationCapability;
>>>>
>>>>
>>>> In v2, I'll follow the interface of virtio-net series, look at
>>>>
>>>> https://patchew.org/QEMU/20250923100110.70862-1-vsementsov@yandex-team.ru/20250923100110.70862-17-vsementsov@yandex-team.ru/
>>>>
>>>> so, it would be migration parameter instead of capability, like
>>>>
>>>> QMP migrate-set-parameters {... backend-transfer = ["vhost-user-blk"] }
>>>>
>>>> and to enable both vhost-user-blk and virtio-net-tap together:
>>>>
>>>> QMP migrate-set-parameters {... backend-transfer = ["vhost-user-blk", "virtio-net-tap"] }
>>>>
>>>
>>> Why do we need two separate migration parameters for vhost-user-blk
>>> and virtio-net-tap? Why not have a single parameter for virtio local
>>> migrations and, if it is set, all backends types which support local
>>> migration can advertise and take advantage of it?
>>
>> As I describe in the commit message https://patchew.org/QEMU/20250923100110.70862-1-vsementsov@yandex-team.ru/20250923100110.70862-17-vsementsov@yandex-team.ru/ :
>>
>>
>> Why not simple boolean? To simplify migration to further versions,
>> when more devices will support backend-transfer migration.
>>
>> Alternatively, we may add per-device option to disable backend-transfer
>> migration, but still:
>>
>> 1. It's more comfortable to set same capabilities/parameters on both
>> source and target QEMU, than care about each device.
>>
>> 2. To not break the design, that machine-type + device options +
>> migration capabilities and parameters are fully define the resulting
>> migration stream. We'll break this if add in future more
>> backend-transfer support in devices under same backend-transfer=true
>> parameter.
>
> ACK on needing a separate migration parameter. Thanks for the references.
>
> I would suggest having the incoming_backend field in the struct
> vhost_user (or maybe even in struct vhost_dev if the tap device
> migration is similar enough) rather than in struct VHostUserBlk, so
> that device-specific code can be kept as similar as possible.
In v2 it will be "backend_transfer" field in struct vhost_dev.
>
>>
>>
>>>
>>>>>
>>>>>
>>>>>> + return s->capabilities[MIGRATION_CAPABILITY_LOCAL_VHOST_USER_BLK];
>>>>>> +}
>>>>>> +
>>>>
>>>> [..]
>>>>
>>>>
>>>> --
>>>> Best regards,
>>>> Vladimir
>>
>>
>> --
>> Best regards,
>> Vladimir
--
Best regards,
Vladimir
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