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VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT was introduced to allow the back-end to suspend in-flight I/O during GET_VRING_BASE instead of draining it, enabling live migration of in-flight requests. However, this behaviour is tied to the protocol feature itself - once negotiated, there is no way for the front-end to tell the back-end to fall back to the normal drain behaviour on a per-stop basis. Introduce a separate message VHOST_USER_GET_VRING_BASE_SKIP_DRAIN (id=45) guarded by a new protocol feature VHOST_USER_PROTOCOL_F_GET_VRING_BASE_SKIP_DRAIN. The message is identical to GET_VRING_BASE except that the back-end must immediately suspend all in-flight I/O and record it in the inflight region. This way the front-end has explicit per-call control: send GET_VRING_BASE for normal drain, send GET_VRING_BASE_SKIP_DRAIN when immediate suspend is needed. The new feature requires both VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT and VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD to be negotiated. Signed-off-by: Alexandr Moshkov <dtalexundeer@yandex-team.ru> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Message-ID: <20260803072853.2920007-3-dtalexundeer@yandex-team.ru>