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[PATCH v6 5/5] vhost-user-blk: support inter-host inflight migration

Alexandr Moshkov posted 5 patches 4 weeks ago
There is a newer version of this series
[PATCH v6 5/5] vhost-user-blk: support inter-host inflight migration
Posted by Alexandr Moshkov 4 weeks ago 
During inter-host migration, waiting for disk requests to be drained
in the vhost-user backend can incur significant downtime.

This can be avoided if QEMU migrates the inflight region in
vhost-user-blk.
Thus, during the qemu migration, with feature flag the vhost-user
back-end can immediately stop vrings, so all in-flight requests will be
migrated to another host.

Signed-off-by: Alexandr Moshkov <dtalexundeer@yandex-team.ru>
---
 hw/block/vhost-user-blk.c          | 28 ++++++++++++++++++++++++++++
 include/hw/virtio/vhost-user-blk.h |  1 +
 2 files changed, 29 insertions(+)

diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
index a8fd90480a..9093e98841 100644
--- a/hw/block/vhost-user-blk.c
+++ b/hw/block/vhost-user-blk.c
@@ -377,6 +377,7 @@ static int vhost_user_blk_init(DeviceState *dev, bool connect, Error **errp)
     vhost_dev_set_config_notifier(&s->dev, &blk_ops);
 
     s->vhost_user.supports_config = true;
+    s->vhost_user.supports_inflight_migration = s->inflight_migration;
     ret = vhost_dev_init(&s->dev, &s->vhost_user, VHOST_BACKEND_TYPE_USER, 0,
                          false, errp);
     if (ret < 0) {
@@ -656,6 +657,27 @@ static struct vhost_dev *vhost_user_blk_get_vhost(VirtIODevice *vdev)
     return &s->dev;
 }
 
+static bool vhost_user_blk_inflight_needed(void *opaque)
+{
+    struct VHostUserBlk *s = opaque;
+
+    bool inflight_migration = vhost_dev_has_feature(&s->dev,
+                        VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT);
+
+    return inflight_migration &&
+           !migrate_local_vhost_user_blk();
+}
+
+static const VMStateDescription vmstate_vhost_user_blk_inflight = {
+    .name = "vhost-user-blk/inflight",
+    .version_id = 1,
+    .needed = vhost_user_blk_inflight_needed,
+    .fields = (const VMStateField[]) {
+        VMSTATE_VHOST_INFLIGHT_REGION(inflight, VHostUserBlk),
+        VMSTATE_END_OF_LIST()
+    },
+};
+
 static bool vhost_user_blk_pre_incoming(void *opaque, Error **errp)
 {
     VHostUserBlk *s = VHOST_USER_BLK(opaque);
@@ -678,6 +700,10 @@ static const VMStateDescription vmstate_vhost_user_blk = {
         VMSTATE_VIRTIO_DEVICE,
         VMSTATE_END_OF_LIST()
     },
+    .subsections = (const VMStateDescription * const []) {
+        &vmstate_vhost_user_blk_inflight,
+        NULL
+    }
 };
 
 static bool vhost_user_needed(void *opaque)
@@ -751,6 +777,8 @@ 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("inflight-migration", VHostUserBlk,
+                     inflight_migration, false),
 };
 
 static void vhost_user_blk_class_init(ObjectClass *klass, const void *data)
diff --git a/include/hw/virtio/vhost-user-blk.h b/include/hw/virtio/vhost-user-blk.h
index b06f55fd6f..e1466e5cf6 100644
--- a/include/hw/virtio/vhost-user-blk.h
+++ b/include/hw/virtio/vhost-user-blk.h
@@ -52,6 +52,7 @@ struct VHostUserBlk {
     bool started_vu;
 
     bool skip_get_vring_base_on_force_shutdown;
+    bool inflight_migration;
 
     bool incoming_backend;
 };
-- 
2.34.1
Re: [PATCH v6 5/5] vhost-user-blk: support inter-host inflight migration
Posted by Peter Xu 3 weeks, 6 days ago 
On Tue, Jan 13, 2026 at 02:58:19PM +0500, Alexandr Moshkov wrote:
> During inter-host migration, waiting for disk requests to be drained
> in the vhost-user backend can incur significant downtime.
> 
> This can be avoided if QEMU migrates the inflight region in
> vhost-user-blk.
> Thus, during the qemu migration, with feature flag the vhost-user
> back-end can immediately stop vrings, so all in-flight requests will be
> migrated to another host.
> 
> Signed-off-by: Alexandr Moshkov <dtalexundeer@yandex-team.ru>
> ---
>  hw/block/vhost-user-blk.c          | 28 ++++++++++++++++++++++++++++
>  include/hw/virtio/vhost-user-blk.h |  1 +
>  2 files changed, 29 insertions(+)
> 
> diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
> index a8fd90480a..9093e98841 100644
> --- a/hw/block/vhost-user-blk.c
> +++ b/hw/block/vhost-user-blk.c
> @@ -377,6 +377,7 @@ static int vhost_user_blk_init(DeviceState *dev, bool connect, Error **errp)
>      vhost_dev_set_config_notifier(&s->dev, &blk_ops);
>  
>      s->vhost_user.supports_config = true;
> +    s->vhost_user.supports_inflight_migration = s->inflight_migration;
>      ret = vhost_dev_init(&s->dev, &s->vhost_user, VHOST_BACKEND_TYPE_USER, 0,
>                           false, errp);
>      if (ret < 0) {
> @@ -656,6 +657,27 @@ static struct vhost_dev *vhost_user_blk_get_vhost(VirtIODevice *vdev)
>      return &s->dev;
>  }
>  
> +static bool vhost_user_blk_inflight_needed(void *opaque)
> +{
> +    struct VHostUserBlk *s = opaque;
> +
> +    bool inflight_migration = vhost_dev_has_feature(&s->dev,
> +                        VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT);
> +
> +    return inflight_migration &&
> +           !migrate_local_vhost_user_blk();

Here's the spot that should depend on migrate_local_vhost_user_blk() from
Vladimilr's RFC patch (again, likely to be renamed..).

Btw, is this check correct against "!migrate_local_vhost_user_blk()"?  I
was expecting the feature off only if local=on, so I expect it to be:

       return inflight_migration && migrate_local_vhost_user_blk();

?

> +}
> +
> +static const VMStateDescription vmstate_vhost_user_blk_inflight = {
> +    .name = "vhost-user-blk/inflight",
> +    .version_id = 1,
> +    .needed = vhost_user_blk_inflight_needed,
> +    .fields = (const VMStateField[]) {
> +        VMSTATE_VHOST_INFLIGHT_REGION(inflight, VHostUserBlk),

One other trivial nitpick while glimpsing over the patch: should we move
the macro definition from previous patch to this one, where it is used?

> +        VMSTATE_END_OF_LIST()
> +    },
> +};
> +
>  static bool vhost_user_blk_pre_incoming(void *opaque, Error **errp)
>  {
>      VHostUserBlk *s = VHOST_USER_BLK(opaque);
> @@ -678,6 +700,10 @@ static const VMStateDescription vmstate_vhost_user_blk = {
>          VMSTATE_VIRTIO_DEVICE,
>          VMSTATE_END_OF_LIST()
>      },
> +    .subsections = (const VMStateDescription * const []) {
> +        &vmstate_vhost_user_blk_inflight,
> +        NULL
> +    }
>  };
>  
>  static bool vhost_user_needed(void *opaque)
> @@ -751,6 +777,8 @@ 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("inflight-migration", VHostUserBlk,
> +                     inflight_migration, false),
>  };
>  
>  static void vhost_user_blk_class_init(ObjectClass *klass, const void *data)
> diff --git a/include/hw/virtio/vhost-user-blk.h b/include/hw/virtio/vhost-user-blk.h
> index b06f55fd6f..e1466e5cf6 100644
> --- a/include/hw/virtio/vhost-user-blk.h
> +++ b/include/hw/virtio/vhost-user-blk.h
> @@ -52,6 +52,7 @@ struct VHostUserBlk {
>      bool started_vu;
>  
>      bool skip_get_vring_base_on_force_shutdown;
> +    bool inflight_migration;
>  
>      bool incoming_backend;
>  };
> -- 
> 2.34.1
> 

-- 
Peter Xu
Re: [PATCH v6 5/5] vhost-user-blk: support inter-host inflight migration
Posted by Alexandr Moshkov 3 weeks, 5 days ago 
On 1/14/26 17:26, Peter Xu wrote:
>> +}
>> +
>> +static const VMStateDescription vmstate_vhost_user_blk_inflight = {
>> +    .name = "vhost-user-blk/inflight",
>> +    .version_id = 1,
>> +    .needed = vhost_user_blk_inflight_needed,
>> +    .fields = (const VMStateField[]) {
>> +        VMSTATE_VHOST_INFLIGHT_REGION(inflight, VHostUserBlk),
> One other trivial nitpick while glimpsing over the patch: should we move
> the macro definition from previous patch to this one, where it is used?
Thanks for reply! I think you right, I'll move this macro.
>
>> +        VMSTATE_END_OF_LIST()
>> +    },
>> +};
>> +
>>   static bool vhost_user_blk_pre_incoming(void *opaque, Error **errp)
>>   {
>>       VHostUserBlk *s = VHOST_USER_BLK(opaque);
>> @@ -678,6 +700,10 @@ static const VMStateDescription vmstate_vhost_user_blk = {
>>           VMSTATE_VIRTIO_DEVICE,
>>           VMSTATE_END_OF_LIST()
>>       },
>> +    .subsections = (const VMStateDescription * const []) {
>> +        &vmstate_vhost_user_blk_inflight,
>> +        NULL
>> +    }
>>   };
>>   
>>   static bool vhost_user_needed(void *opaque)
>> @@ -751,6 +777,8 @@ 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("inflight-migration", VHostUserBlk,
>> +                     inflight_migration, false),
>>   };
>>   
>>   static void vhost_user_blk_class_init(ObjectClass *klass, const void *data)
>> diff --git a/include/hw/virtio/vhost-user-blk.h b/include/hw/virtio/vhost-user-blk.h
>> index b06f55fd6f..e1466e5cf6 100644
>> --- a/include/hw/virtio/vhost-user-blk.h
>> +++ b/include/hw/virtio/vhost-user-blk.h
>> @@ -52,6 +52,7 @@ struct VHostUserBlk {
>>       bool started_vu;
>>   
>>       bool skip_get_vring_base_on_force_shutdown;
>> +    bool inflight_migration;
>>   
>>       bool incoming_backend;
>>   };
>> -- 
>> 2.34.1
>>

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