In case of migration of QEMU from the new version (where the
inllight-migration parameter is present), to the old one (where it is
absent) there is no way to disable this feature on the backend during
runtime.

This commit slightly changes the semantics of the protocol feature
VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT. Enabling this feature
adds a new parameter for GET_VRING_BASE, which allows to control the
drain in-flight requests on the backend.
Thus, QEMU will be able to turn this feature on GET_VRING_BASE off and
on anytime.

In vhost-user-blk use inflight_migration param to enable skip_drain to
suspend in-flight I/O requests, and then migrate them throught inflight
subsection.

Also now QEMU will always try to setup
VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT protocol featrue with
backend. This will allow to use skip_drain parameter on GET_VRING_BASE
message.

Signed-off-by: Alexandr Moshkov <dtalexundeer@yandex-team.ru>
---
 docs/interop/vhost-user.rst    |  6 ++----
 hw/block/vhost-user-blk.c      | 29 +++++++++++++++++++++++------
 hw/virtio/vhost-user.c         |  3 +--
 hw/virtio/vhost.c              |  4 +---
 include/hw/virtio/vhost-user.h |  1 -
 5 files changed, 27 insertions(+), 16 deletions(-)

diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst
index bfa75ff9a3..63efc87264 100644
--- a/docs/interop/vhost-user.rst
+++ b/docs/interop/vhost-user.rst
@@ -1255,14 +1255,12 @@ Front-end message types
   *suspended*, see :ref:`Suspended device state
   <suspended_device_state>`.
 
-  The request payload's *num* field is currently reserved and must be
-  set to 0.
-
   By default, the back-end must complete all inflight I/O requests for the
   specified vring before stopping it.
 
   If the ``VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT`` protocol
-  feature has been negotiated, the back-end may suspend in-flight I/O
+  feature has been negotiated, using request payload's *num* field,
+  when *num* is set to 1, QEMU can tell the back-end to suspend in-flight I/O
   requests and record them as described in :ref:`Inflight I/O tracking
   <inflight_io_tracking>` instead of completing them before stopping the vring.
   How to suspend an in-flight request depends on the implementation of the back-end
diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
index 1dc49c104e..8cc80eb0c3 100644
--- a/hw/block/vhost-user-blk.c
+++ b/hw/block/vhost-user-blk.c
@@ -134,10 +134,7 @@ static bool vhost_user_blk_inflight_needed(void *opaque)
 {
     struct VHostUserBlk *s = opaque;
 
-    bool inflight_migration = virtio_has_feature(s->dev.protocol_features,
-                               VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT);
-
-    return inflight_migration;
+    return s->inflight_migration;
 }
 
 
@@ -232,11 +229,14 @@ static int vhost_user_blk_stop(VirtIODevice *vdev)
         return 0;
     }
 
+    bool skip_drain = vhost_user_blk_inflight_needed(s) &&
+                      runstate_check(RUN_STATE_FINISH_MIGRATE);
+
     force_stop = s->skip_get_vring_base_on_force_shutdown &&
                  qemu_force_shutdown_requested();
 
     ret = force_stop ? vhost_dev_force_stop(&s->dev, vdev, true) :
-                       vhost_dev_stop(&s->dev, vdev, true, false);
+                       vhost_dev_stop(&s->dev, vdev, true, skip_drain);
 
     if (k->set_guest_notifiers(qbus->parent, s->dev.nvqs, false) < 0) {
         error_report("vhost guest notifier cleanup failed: %d", ret);
@@ -364,7 +364,6 @@ static int vhost_user_blk_connect(DeviceState *dev, 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,
                          errp);
     if (ret < 0) {
@@ -580,10 +579,28 @@ static struct vhost_dev *vhost_user_blk_get_vhost(VirtIODevice *vdev)
     return &s->dev;
 }
 
+static bool vhost_user_blk_pre_save(void *opaqueue, Error **errp)
+{
+    VHostUserBlk *s = VHOST_USER_BLK(vdev);
+
+    bool inflight_migration_enabled = vhost_user_has_protocol_feature(&s->dev,
+                            VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT);
+    if (vhost_user_blk_inflight_needed(s) && !inflight_migration_enabled) {
+        error_setg(errp, "can't migrate vhost-user-blk device: "
+                         "backend doesn't support "
+                         "VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT "
+                         "protocol feature");
+        return false;
+    }
+
+    return true;
+}
+
 static const VMStateDescription vmstate_vhost_user_blk_inflight = {
     .name = "vhost-user-blk/inflight",
     .version_id = 1,
     .needed = vhost_user_blk_inflight_needed,
+    .pre_save_errp = vhost_user_blk_pre_save,
     .fields = (const VMStateField[]) {
         VMSTATE_VHOST_INFLIGHT_REGION(inflight, VHostUserBlk),
         VMSTATE_END_OF_LIST()
diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index bb8f8eab77..ed95ec7523 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -2225,8 +2225,7 @@ static int vhost_user_backend_init(struct vhost_dev *dev, void *opaque,
             }
         }
 
-        if (!u->user->supports_inflight_migration ||
-            !virtio_has_feature(protocol_features,
+        if (!virtio_has_feature(protocol_features,
                                 VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD)) {
             protocol_features &= ~(1ULL <<
                                VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT);
diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 4e196fc773..c04bb53159 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -1390,12 +1390,10 @@ static int do_vhost_virtqueue_stop(struct vhost_dev *dev,
                                    unsigned idx, bool force,
                                    bool skip_drain)
 {
-    /* TODO: support skip drain */
-    assert(!skip_drain);
-
     int vhost_vq_index = dev->vhost_ops->vhost_get_vq_index(dev, idx);
     struct vhost_vring_state state = {
         .index = vhost_vq_index,
+        .num = skip_drain,
     };
     int r = 0;
 
diff --git a/include/hw/virtio/vhost-user.h b/include/hw/virtio/vhost-user.h
index 53fe996686..c95bad5ddc 100644
--- a/include/hw/virtio/vhost-user.h
+++ b/include/hw/virtio/vhost-user.h
@@ -69,7 +69,6 @@ typedef struct VhostUserState {
     GPtrArray *notifiers;
     int memory_slots;
     bool supports_config;
-    bool supports_inflight_migration;
 } VhostUserState;
 
 /**
-- 
2.34.1

On Wed, Mar 11, 2026 at 01:47:28PM +0500, Alexandr Moshkov wrote:
> In case of migration of QEMU from the new version (where the
> inllight-migration parameter is present), to the old one (where it is
> absent) there is no way to disable this feature on the backend during
> runtime.
> 
> This commit slightly changes the semantics of the protocol feature
> VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT. Enabling this feature
> adds a new parameter for GET_VRING_BASE, which allows to control the
> drain in-flight requests on the backend.
> Thus, QEMU will be able to turn this feature on GET_VRING_BASE off and
> on anytime.
> 
> In vhost-user-blk use inflight_migration param to enable skip_drain to
> suspend in-flight I/O requests, and then migrate them throught inflight
> subsection.
> 
> Also now QEMU will always try to setup
> VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT protocol featrue with
> backend. This will allow to use skip_drain parameter on GET_VRING_BASE
> message.
> 
> Signed-off-by: Alexandr Moshkov <dtalexundeer@yandex-team.ru>
> ---
>  docs/interop/vhost-user.rst    |  6 ++----
>  hw/block/vhost-user-blk.c      | 29 +++++++++++++++++++++++------
>  hw/virtio/vhost-user.c         |  3 +--
>  hw/virtio/vhost.c              |  4 +---
>  include/hw/virtio/vhost-user.h |  1 -
>  5 files changed, 27 insertions(+), 16 deletions(-)
> 
> diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst
> index bfa75ff9a3..63efc87264 100644
> --- a/docs/interop/vhost-user.rst
> +++ b/docs/interop/vhost-user.rst
> @@ -1255,14 +1255,12 @@ Front-end message types
>    *suspended*, see :ref:`Suspended device state
>    <suspended_device_state>`.
>  
> -  The request payload's *num* field is currently reserved and must be
> -  set to 0.
> -
>    By default, the back-end must complete all inflight I/O requests for the
>    specified vring before stopping it.
>  
>    If the ``VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT`` protocol
> -  feature has been negotiated, the back-end may suspend in-flight I/O
> +  feature has been negotiated, using request payload's *num* field,
> +  when *num* is set to 1, QEMU can tell the back-end to suspend in-flight I/O
>    requests and record them as described in :ref:`Inflight I/O tracking
>    <inflight_io_tracking>` instead of completing them before stopping the vring.
>    How to suspend an in-flight request depends on the implementation of the back-end
> diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
> index 1dc49c104e..8cc80eb0c3 100644
> --- a/hw/block/vhost-user-blk.c
> +++ b/hw/block/vhost-user-blk.c
> @@ -134,10 +134,7 @@ static bool vhost_user_blk_inflight_needed(void *opaque)
>  {
>      struct VHostUserBlk *s = opaque;
>  
> -    bool inflight_migration = virtio_has_feature(s->dev.protocol_features,
> -                               VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT);
> -
> -    return inflight_migration;
> +    return s->inflight_migration;
>  }
>  
>  
> @@ -232,11 +229,14 @@ static int vhost_user_blk_stop(VirtIODevice *vdev)
>          return 0;
>      }
>  
> +    bool skip_drain = vhost_user_blk_inflight_needed(s) &&
> +                      runstate_check(RUN_STATE_FINISH_MIGRATE);
> +
>      force_stop = s->skip_get_vring_base_on_force_shutdown &&
>                   qemu_force_shutdown_requested();
>  
>      ret = force_stop ? vhost_dev_force_stop(&s->dev, vdev, true) :
> -                       vhost_dev_stop(&s->dev, vdev, true, false);
> +                       vhost_dev_stop(&s->dev, vdev, true, skip_drain);
>  
>      if (k->set_guest_notifiers(qbus->parent, s->dev.nvqs, false) < 0) {
>          error_report("vhost guest notifier cleanup failed: %d", ret);
> @@ -364,7 +364,6 @@ static int vhost_user_blk_connect(DeviceState *dev, 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,
>                           errp);
>      if (ret < 0) {
> @@ -580,10 +579,28 @@ static struct vhost_dev *vhost_user_blk_get_vhost(VirtIODevice *vdev)
>      return &s->dev;
>  }
>  
> +static bool vhost_user_blk_pre_save(void *opaqueue, Error **errp)
> +{
> +    VHostUserBlk *s = VHOST_USER_BLK(vdev);

This won't compile. "opaqueue" is unused and the vdev variable does not
exist.

> +
> +    bool inflight_migration_enabled = vhost_user_has_protocol_feature(&s->dev,

vhost_user_has_protocol_feature() does not exist.

> +                            VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT);
> +    if (vhost_user_blk_inflight_needed(s) && !inflight_migration_enabled) {
> +        error_setg(errp, "can't migrate vhost-user-blk device: "
> +                         "backend doesn't support "
> +                         "VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT "
> +                         "protocol feature");
> +        return false;
> +    }
> +
> +    return true;
> +}
> +
>  static const VMStateDescription vmstate_vhost_user_blk_inflight = {
>      .name = "vhost-user-blk/inflight",
>      .version_id = 1,
>      .needed = vhost_user_blk_inflight_needed,
> +    .pre_save_errp = vhost_user_blk_pre_save,
>      .fields = (const VMStateField[]) {
>          VMSTATE_VHOST_INFLIGHT_REGION(inflight, VHostUserBlk),
>          VMSTATE_END_OF_LIST()
> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> index bb8f8eab77..ed95ec7523 100644
> --- a/hw/virtio/vhost-user.c
> +++ b/hw/virtio/vhost-user.c
> @@ -2225,8 +2225,7 @@ static int vhost_user_backend_init(struct vhost_dev *dev, void *opaque,
>              }
>          }
>  
> -        if (!u->user->supports_inflight_migration ||
> -            !virtio_has_feature(protocol_features,
> +        if (!virtio_has_feature(protocol_features,
>                                  VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD)) {
>              protocol_features &= ~(1ULL <<
>                                 VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT);
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index 4e196fc773..c04bb53159 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -1390,12 +1390,10 @@ static int do_vhost_virtqueue_stop(struct vhost_dev *dev,
>                                     unsigned idx, bool force,
>                                     bool skip_drain)
>  {
> -    /* TODO: support skip drain */
> -    assert(!skip_drain);

The following assertion would be useful:

  if (skip_drain) {
      assert(virtio_has_feature(...protocol_features...,
              VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT));
  }

> -
>      int vhost_vq_index = dev->vhost_ops->vhost_get_vq_index(dev, idx);
>      struct vhost_vring_state state = {
>          .index = vhost_vq_index,
> +        .num = skip_drain,
>      };
>      int r = 0;
>  
> diff --git a/include/hw/virtio/vhost-user.h b/include/hw/virtio/vhost-user.h
> index 53fe996686..c95bad5ddc 100644
> --- a/include/hw/virtio/vhost-user.h
> +++ b/include/hw/virtio/vhost-user.h
> @@ -69,7 +69,6 @@ typedef struct VhostUserState {
>      GPtrArray *notifiers;
>      int memory_slots;
>      bool supports_config;
> -    bool supports_inflight_migration;
>  } VhostUserState;
>  
>  /**
> -- 
> 2.34.1
> 

On 3/26/26 20:52, Stefan Hajnoczi wrote:
> On Wed, Mar 11, 2026 at 01:47:28PM +0500, Alexandr Moshkov wrote:
>> In case of migration of QEMU from the new version (where the
>> inllight-migration parameter is present), to the old one (where it is
>> absent) there is no way to disable this feature on the backend during
>> runtime.
>>
>> This commit slightly changes the semantics of the protocol feature
>> VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT. Enabling this feature
>> adds a new parameter for GET_VRING_BASE, which allows to control the
>> drain in-flight requests on the backend.
>> Thus, QEMU will be able to turn this feature on GET_VRING_BASE off and
>> on anytime.
>>
>> In vhost-user-blk use inflight_migration param to enable skip_drain to
>> suspend in-flight I/O requests, and then migrate them throught inflight
>> subsection.
>>
>> Also now QEMU will always try to setup
>> VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT protocol featrue with
>> backend. This will allow to use skip_drain parameter on GET_VRING_BASE
>> message.
>>
>> Signed-off-by: Alexandr Moshkov <dtalexundeer@yandex-team.ru>
>> ---
>>   docs/interop/vhost-user.rst    |  6 ++----
>>   hw/block/vhost-user-blk.c      | 29 +++++++++++++++++++++++------
>>   hw/virtio/vhost-user.c         |  3 +--
>>   hw/virtio/vhost.c              |  4 +---
>>   include/hw/virtio/vhost-user.h |  1 -
>>   5 files changed, 27 insertions(+), 16 deletions(-)
>>
>> diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst
>> index bfa75ff9a3..63efc87264 100644
>> --- a/docs/interop/vhost-user.rst
>> +++ b/docs/interop/vhost-user.rst
>> @@ -1255,14 +1255,12 @@ Front-end message types
>>     *suspended*, see :ref:`Suspended device state
>>     <suspended_device_state>`.
>>   
>> -  The request payload's *num* field is currently reserved and must be
>> -  set to 0.
>> -
>>     By default, the back-end must complete all inflight I/O requests for the
>>     specified vring before stopping it.
>>   
>>     If the ``VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT`` protocol
>> -  feature has been negotiated, the back-end may suspend in-flight I/O
>> +  feature has been negotiated, using request payload's *num* field,
>> +  when *num* is set to 1, QEMU can tell the back-end to suspend in-flight I/O
>>     requests and record them as described in :ref:`Inflight I/O tracking
>>     <inflight_io_tracking>` instead of completing them before stopping the vring.
>>     How to suspend an in-flight request depends on the implementation of the back-end
>> diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
>> index 1dc49c104e..8cc80eb0c3 100644
>> --- a/hw/block/vhost-user-blk.c
>> +++ b/hw/block/vhost-user-blk.c
>> @@ -134,10 +134,7 @@ static bool vhost_user_blk_inflight_needed(void *opaque)
>>   {
>>       struct VHostUserBlk *s = opaque;
>>   
>> -    bool inflight_migration = virtio_has_feature(s->dev.protocol_features,
>> -                               VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT);
>> -
>> -    return inflight_migration;
>> +    return s->inflight_migration;
>>   }
>>   
>>   
>> @@ -232,11 +229,14 @@ static int vhost_user_blk_stop(VirtIODevice *vdev)
>>           return 0;
>>       }
>>   
>> +    bool skip_drain = vhost_user_blk_inflight_needed(s) &&
>> +                      runstate_check(RUN_STATE_FINISH_MIGRATE);
>> +
>>       force_stop = s->skip_get_vring_base_on_force_shutdown &&
>>                    qemu_force_shutdown_requested();
>>   
>>       ret = force_stop ? vhost_dev_force_stop(&s->dev, vdev, true) :
>> -                       vhost_dev_stop(&s->dev, vdev, true, false);
>> +                       vhost_dev_stop(&s->dev, vdev, true, skip_drain);
>>   
>>       if (k->set_guest_notifiers(qbus->parent, s->dev.nvqs, false) < 0) {
>>           error_report("vhost guest notifier cleanup failed: %d", ret);
>> @@ -364,7 +364,6 @@ static int vhost_user_blk_connect(DeviceState *dev, 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,
>>                            errp);
>>       if (ret < 0) {
>> @@ -580,10 +579,28 @@ static struct vhost_dev *vhost_user_blk_get_vhost(VirtIODevice *vdev)
>>       return &s->dev;
>>   }
>>   
>> +static bool vhost_user_blk_pre_save(void *opaqueue, Error **errp)
>> +{
>> +    VHostUserBlk *s = VHOST_USER_BLK(vdev);
> This won't compile. "opaqueue" is unused and the vdev variable does not
> exist.
>
>> +
>> +    bool inflight_migration_enabled = vhost_user_has_protocol_feature(&s->dev,
> vhost_user_has_protocol_feature() does not exist.
>
>> +                            VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT);
>> +    if (vhost_user_blk_inflight_needed(s) && !inflight_migration_enabled) {
>> +        error_setg(errp, "can't migrate vhost-user-blk device: "
>> +                         "backend doesn't support "
>> +                         "VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT "
>> +                         "protocol feature");
>> +        return false;
>> +    }
>> +
>> +    return true;
>> +}
>> +
>>   static const VMStateDescription vmstate_vhost_user_blk_inflight = {
>>       .name = "vhost-user-blk/inflight",
>>       .version_id = 1,
>>       .needed = vhost_user_blk_inflight_needed,
>> +    .pre_save_errp = vhost_user_blk_pre_save,
>>       .fields = (const VMStateField[]) {
>>           VMSTATE_VHOST_INFLIGHT_REGION(inflight, VHostUserBlk),
>>           VMSTATE_END_OF_LIST()
>> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
>> index bb8f8eab77..ed95ec7523 100644
>> --- a/hw/virtio/vhost-user.c
>> +++ b/hw/virtio/vhost-user.c
>> @@ -2225,8 +2225,7 @@ static int vhost_user_backend_init(struct vhost_dev *dev, void *opaque,
>>               }
>>           }
>>   
>> -        if (!u->user->supports_inflight_migration ||
>> -            !virtio_has_feature(protocol_features,
>> +        if (!virtio_has_feature(protocol_features,
>>                                   VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD)) {
>>               protocol_features &= ~(1ULL <<
>>                                  VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT);
>> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
>> index 4e196fc773..c04bb53159 100644
>> --- a/hw/virtio/vhost.c
>> +++ b/hw/virtio/vhost.c
>> @@ -1390,12 +1390,10 @@ static int do_vhost_virtqueue_stop(struct vhost_dev *dev,
>>                                      unsigned idx, bool force,
>>                                      bool skip_drain)
>>   {
>> -    /* TODO: support skip drain */
>> -    assert(!skip_drain);
> The following assertion would be useful:
>
>    if (skip_drain) {
>        assert(virtio_has_feature(...protocol_features...,
>                VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT));
>    }
Thanks for reply! I'll fix it all
>> -
>>       int vhost_vq_index = dev->vhost_ops->vhost_get_vq_index(dev, idx);
>>       struct vhost_vring_state state = {
>>           .index = vhost_vq_index,
>> +        .num = skip_drain,
>>       };
>>       int r = 0;
>>   
>> diff --git a/include/hw/virtio/vhost-user.h b/include/hw/virtio/vhost-user.h
>> index 53fe996686..c95bad5ddc 100644
>> --- a/include/hw/virtio/vhost-user.h
>> +++ b/include/hw/virtio/vhost-user.h
>> @@ -69,7 +69,6 @@ typedef struct VhostUserState {
>>       GPtrArray *notifiers;
>>       int memory_slots;
>>       bool supports_config;
>> -    bool supports_inflight_migration;
>>   } VhostUserState;
>>   
>>   /**
>> -- 
>> 2.34.1
>>

On 11.03.26 11:47, Alexandr Moshkov wrote:
> In case of migration of QEMU from the new version (where the
> inllight-migration parameter is present), to the old one (where it is
> absent) there is no way to disable this feature on the backend during
> runtime.
> 
> This commit slightly changes the semantics of the protocol feature
> VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT. Enabling this feature
> adds a new parameter for GET_VRING_BASE, which allows to control the
> drain in-flight requests on the backend.
> Thus, QEMU will be able to turn this feature on GET_VRING_BASE off and
> on anytime.
> 
> In vhost-user-blk use inflight_migration param to enable skip_drain to
> suspend in-flight I/O requests, and then migrate them throught inflight
> subsection.
> 
> Also now QEMU will always try to setup
> VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT protocol featrue with
> backend. This will allow to use skip_drain parameter on GET_VRING_BASE
> message.
> 
> Signed-off-by: Alexandr Moshkov<dtalexundeer@yandex-team.ru>

Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>


Is it too late for 11.0, to fix protocol disadvantage we've added?

Or could it be fixed in 11.1?


-- 
Best regards,
Vladimir