Re: [PATCH v5 5/5] vhost-user-blk: support inter-host inflight migration

On 1/12/26 23:19, Stefan Hajnoczi wrote:
> On Mon, Jan 12, 2026 at 04:45:03PM +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 <[email protected]>
>> ---
>>   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..5e44f6253c 100644
>> --- a/hw/block/vhost-user-blk.c
>> +++ b/hw/block/vhost-user-blk.c
>> @@ -656,6 +656,28 @@ 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_drain = vhost_dev_has_feature(&s->dev,
>> +                        VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT);
> VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT must only be negotiated
> when inflight_migration is enabled. Otherwise the backend will use this
> feature even though vhost_user_blk_inflight_needed() skips migrating the
> in-flight region.
Oh, I understand now. I'll fix this too, thanks!