On Tue, Feb 24, 2026 at 12:50:53PM +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. > > Signed-off-by: Alexandr Moshkov <[email protected]> > --- > backends/cryptodev-vhost.c | 2 +- > backends/vhost-user.c | 2 +- > docs/interop/vhost-user.rst | 3 ++- > hw/block/vhost-user-blk.c | 2 +- > hw/net/vhost_net.c | 9 +++++---- > hw/scsi/vhost-scsi-common.c | 2 +- > hw/virtio/vdpa-dev.c | 2 +- > hw/virtio/vhost-user-base.c | 2 +- > hw/virtio/vhost-user-fs.c | 2 +- > hw/virtio/vhost-user-scmi.c | 2 +- > hw/virtio/vhost-vsock-common.c | 2 +- > hw/virtio/vhost.c | 24 +++++++++++++++--------- > include/hw/virtio/vhost.h | 7 +++++-- > 13 files changed, 36 insertions(+), 25 deletions(-) > > diff --git a/backends/cryptodev-vhost.c b/backends/cryptodev-vhost.c > index 943680a23a..7a457380d0 100644 > --- a/backends/cryptodev-vhost.c > +++ b/backends/cryptodev-vhost.c > @@ -110,7 +110,7 @@ static void > cryptodev_vhost_stop_one(CryptoDevBackendVhost *crypto, > VirtIODevice *dev) > { > - vhost_dev_stop(&crypto->dev, dev, false); > + vhost_dev_stop(&crypto->dev, dev, false, false); > vhost_dev_disable_notifiers(&crypto->dev, dev); > } > > diff --git a/backends/vhost-user.c b/backends/vhost-user.c > index 42845329e7..10be713ebd 100644 > --- a/backends/vhost-user.c > +++ b/backends/vhost-user.c > @@ -108,7 +108,7 @@ vhost_user_backend_stop(VhostUserBackend *b) > return 0; > } > > - ret = vhost_dev_stop(&b->dev, b->vdev, true); > + ret = vhost_dev_stop(&b->dev, b->vdev, true, false); > > if (k->set_guest_notifiers && > k->set_guest_notifiers(qbus->parent, b->dev.nvqs, false) < 0) { > diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst > index bfa75ff9a3..5b944322b4 100644 > --- a/docs/interop/vhost-user.rst > +++ b/docs/interop/vhost-user.rst > @@ -1262,7 +1262,8 @@ Front-end message types > 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
This changes the behavior of an existing feature bit. How can the
front-end detect that the back-end supports this new behavior?
> 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 c151e83677..7f2067d6cf 100644
> --- a/hw/block/vhost-user-blk.c
> +++ b/hw/block/vhost-user-blk.c
> @@ -225,7 +225,7 @@ static int vhost_user_blk_stop(VirtIODevice *vdev)
> qemu_force_shutdown_requested();
>
> ret = force_stop ? vhost_dev_force_stop(&s->dev, vdev, true) :
> - vhost_dev_stop(&s->dev, vdev, true);
> + vhost_dev_stop(&s->dev, vdev, true, false);
>
> if (k->set_guest_notifiers(qbus->parent, s->dev.nvqs, false) < 0) {
> error_report("vhost guest notifier cleanup failed: %d", ret);
> diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
> index a8ee18a912..604f19e03a 100644
> --- a/hw/net/vhost_net.c
> +++ b/hw/net/vhost_net.c
> @@ -384,7 +384,7 @@ fail:
> if (net->nc->info->poll) {
> net->nc->info->poll(net->nc, true);
> }
> - vhost_dev_stop(&net->dev, dev, false);
> + vhost_dev_stop(&net->dev, dev, false, false);
> fail_start:
> return r;
> }
> @@ -403,7 +403,7 @@ static void vhost_net_stop_one(struct vhost_net *net,
> if (net->nc->info->poll) {
> net->nc->info->poll(net->nc, true);
> }
> - vhost_dev_stop(&net->dev, dev, false);
> + vhost_dev_stop(&net->dev, dev, false, false);
> if (net->nc->info->stop) {
> net->nc->info->stop(net->nc);
> }
> @@ -641,7 +641,8 @@ void vhost_net_virtqueue_reset(VirtIODevice *vdev,
> NetClientState *nc,
> vhost_virtqueue_stop(&net->dev,
> vdev,
> net->dev.vqs + idx,
> - net->dev.vq_index + idx);
> + net->dev.vq_index + idx,
> + false);
> }
>
> int vhost_net_virtqueue_restart(VirtIODevice *vdev, NetClientState *nc,
> @@ -691,7 +692,7 @@ err_start:
> assert(ret >= 0);
> }
>
> - vhost_dev_stop(&net->dev, vdev, false);
> + vhost_dev_stop(&net->dev, vdev, false, false);
>
> return r;
> }
> diff --git a/hw/scsi/vhost-scsi-common.c b/hw/scsi/vhost-scsi-common.c
> index 0bb4305de6..41c1e45aac 100644
> --- a/hw/scsi/vhost-scsi-common.c
> +++ b/hw/scsi/vhost-scsi-common.c
> @@ -108,7 +108,7 @@ int vhost_scsi_common_stop(VHostSCSICommon *vsc)
> VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
> int ret = 0;
>
> - ret = vhost_dev_stop(&vsc->dev, vdev, true);
> + ret = vhost_dev_stop(&vsc->dev, vdev, true, false);
>
> if (k->set_guest_notifiers) {
> int r = k->set_guest_notifiers(qbus->parent, vsc->dev.nvqs, false);
> diff --git a/hw/virtio/vdpa-dev.c b/hw/virtio/vdpa-dev.c
> index 4532d63653..7279f18442 100644
> --- a/hw/virtio/vdpa-dev.c
> +++ b/hw/virtio/vdpa-dev.c
> @@ -301,7 +301,7 @@ static void vhost_vdpa_device_stop(VirtIODevice *vdev)
> return;
> }
>
> - vhost_dev_stop(&s->dev, vdev, false);
> + vhost_dev_stop(&s->dev, vdev, false, false);
>
> ret = k->set_guest_notifiers(qbus->parent, s->dev.nvqs, false);
> if (ret < 0) {
> diff --git a/hw/virtio/vhost-user-base.c b/hw/virtio/vhost-user-base.c
> index 01ab9ca56b..9d3875a04b 100644
> --- a/hw/virtio/vhost-user-base.c
> +++ b/hw/virtio/vhost-user-base.c
> @@ -77,7 +77,7 @@ static int vub_stop(VirtIODevice *vdev)
> return 0;
> }
>
> - ret = vhost_dev_stop(&vub->vhost_dev, vdev, true);
> + ret = vhost_dev_stop(&vub->vhost_dev, vdev, true, false);
>
> if (k->set_guest_notifiers(qbus->parent, vub->vhost_dev.nvqs, false) <
> 0) {
> error_report("vhost guest notifier cleanup failed: %d", ret);
> diff --git a/hw/virtio/vhost-user-fs.c b/hw/virtio/vhost-user-fs.c
> index ad6fcacf06..2f6f6df67f 100644
> --- a/hw/virtio/vhost-user-fs.c
> +++ b/hw/virtio/vhost-user-fs.c
> @@ -111,7 +111,7 @@ static int vuf_stop(VirtIODevice *vdev)
> return 0;
> }
>
> - ret = vhost_dev_stop(&fs->vhost_dev, vdev, true);
> + ret = vhost_dev_stop(&fs->vhost_dev, vdev, true, false);
>
> if (k->set_guest_notifiers(qbus->parent, fs->vhost_dev.nvqs, false) < 0)
> {
> error_report("vhost guest notifier cleanup failed: %d", ret);
> diff --git a/hw/virtio/vhost-user-scmi.c b/hw/virtio/vhost-user-scmi.c
> index f9264c4374..dbde342a6e 100644
> --- a/hw/virtio/vhost-user-scmi.c
> +++ b/hw/virtio/vhost-user-scmi.c
> @@ -101,7 +101,7 @@ static int vu_scmi_stop(VirtIODevice *vdev)
> return 0;
> }
>
> - ret = vhost_dev_stop(vhost_dev, vdev, true);
> + ret = vhost_dev_stop(vhost_dev, vdev, true, false);
>
> if (k->set_guest_notifiers(qbus->parent, vhost_dev->nvqs, false) < 0) {
> error_report("vhost guest notifier cleanup failed: %d", ret);
> diff --git a/hw/virtio/vhost-vsock-common.c b/hw/virtio/vhost-vsock-common.c
> index b33def900a..3d086ed825 100644
> --- a/hw/virtio/vhost-vsock-common.c
> +++ b/hw/virtio/vhost-vsock-common.c
> @@ -106,7 +106,7 @@ int vhost_vsock_common_stop(VirtIODevice *vdev)
> return 0;
> }
>
> - ret = vhost_dev_stop(&vvc->vhost_dev, vdev, true);
> + ret = vhost_dev_stop(&vvc->vhost_dev, vdev, true, false);
>
> if (k->set_guest_notifiers(qbus->parent, vvc->vhost_dev.nvqs, false) <
> 0) {
> error_report("vhost guest notifier cleanup failed: %d", ret);
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index b4cdb7762f..c04bb53159 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -1387,11 +1387,13 @@ fail_alloc_desc:
> static int do_vhost_virtqueue_stop(struct vhost_dev *dev,
> struct VirtIODevice *vdev,
> struct vhost_virtqueue *vq,
> - unsigned idx, bool force)
> + unsigned idx, bool force,
> + bool 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;
>
> @@ -1439,9 +1441,10 @@ static int do_vhost_virtqueue_stop(struct vhost_dev
> *dev,
> int vhost_virtqueue_stop(struct vhost_dev *dev,
> struct VirtIODevice *vdev,
> struct vhost_virtqueue *vq,
> - unsigned idx)
> + unsigned idx,
> + bool skip_drain)
> {
> - return do_vhost_virtqueue_stop(dev, vdev, vq, idx, false);
> + return do_vhost_virtqueue_stop(dev, vdev, vq, idx, false, skip_drain);
> }
>
> static int vhost_virtqueue_set_busyloop_timeout(struct vhost_dev *dev,
> @@ -2220,7 +2223,8 @@ fail_vq:
> vhost_virtqueue_stop(hdev,
> vdev,
> hdev->vqs + i,
> - hdev->vq_index + i);
> + hdev->vq_index + i,
> + false);
> }
>
> fail_mem:
> @@ -2235,7 +2239,7 @@ fail_features:
>
> /* Host notifiers must be enabled at this point. */
> static int do_vhost_dev_stop(struct vhost_dev *hdev, VirtIODevice *vdev,
> - bool vrings, bool force)
> + bool vrings, bool force, bool skip_drain)
> {
> int i;
> int rc = 0;
> @@ -2262,7 +2266,8 @@ static int do_vhost_dev_stop(struct vhost_dev *hdev,
> VirtIODevice *vdev,
> vdev,
> hdev->vqs + i,
> hdev->vq_index + i,
> - force);
> + force,
> + skip_drain);
> }
> if (hdev->vhost_ops->vhost_reset_status) {
> hdev->vhost_ops->vhost_reset_status(hdev);
> @@ -2282,15 +2287,16 @@ static int do_vhost_dev_stop(struct vhost_dev *hdev,
> VirtIODevice *vdev,
> return rc;
> }
>
> -int vhost_dev_stop(struct vhost_dev *hdev, VirtIODevice *vdev, bool vrings)
> +int vhost_dev_stop(struct vhost_dev *hdev, VirtIODevice *vdev, bool vrings,
> + bool skip_drain)
> {
> - return do_vhost_dev_stop(hdev, vdev, vrings, false);
> + return do_vhost_dev_stop(hdev, vdev, vrings, false, skip_drain);
> }
>
> int vhost_dev_force_stop(struct vhost_dev *hdev, VirtIODevice *vdev,
> bool vrings)
> {
> - return do_vhost_dev_stop(hdev, vdev, vrings, true);
> + return do_vhost_dev_stop(hdev, vdev, vrings, true, false);
> }
>
> int vhost_net_set_backend(struct vhost_dev *hdev,
> diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h
> index 89817bd848..3881f6784b 100644
> --- a/include/hw/virtio/vhost.h
> +++ b/include/hw/virtio/vhost.h
> @@ -233,6 +233,7 @@ int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice
> *vdev, bool vrings);
> * @hdev: common vhost_dev structure
> * @vdev: the VirtIODevice structure
> * @vrings: true to have vrings disabled in this call
> + * @skip_drain: true to notice back-end to skip draining all in-flight
> requests
> *
> * Stop the vhost device. After the device is stopped the notifiers
> * can be disabled (@vhost_dev_disable_notifiers) and the device can
> @@ -240,7 +241,8 @@ int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice
> *vdev, bool vrings);
> *
> * Return: 0 on success, != 0 on error when stopping dev.
> */
> -int vhost_dev_stop(struct vhost_dev *hdev, VirtIODevice *vdev, bool vrings);
> +int vhost_dev_stop(struct vhost_dev *hdev, VirtIODevice *vdev, bool vrings,
> + bool skip_drain);
>
> /**
> * vhost_dev_force_stop() - force stop the vhost device
> @@ -398,7 +400,8 @@ int vhost_device_iotlb_miss(struct vhost_dev *dev,
> uint64_t iova, int write);
> int vhost_virtqueue_start(struct vhost_dev *dev, struct VirtIODevice *vdev,
> struct vhost_virtqueue *vq, unsigned idx);
> int vhost_virtqueue_stop(struct vhost_dev *dev, struct VirtIODevice *vdev,
> - struct vhost_virtqueue *vq, unsigned idx);
> + struct vhost_virtqueue *vq, unsigned idx,
> + bool skip_drain);
>
> void vhost_dev_reset_inflight(struct vhost_inflight *inflight);
> void vhost_dev_free_inflight(struct vhost_inflight *inflight);
> --
> 2.34.1
>
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