Acked-by: Raphael Norwitz <raphael.s.norwitz@gmail.com>
On Wed, Aug 13, 2025 at 1:01 PM Vladimir Sementsov-Ogievskiy
<vsementsov@yandex-team.ru> wrote:
>
> This field is mostly unused and sometimes confusing (we even have
> a TODO-like comment to drop it). Let's finally do.
>
> The field is used to held VHOST_USER_F_PROTOCOL_FEATURES for vhost-user
> and/or VHOST_NET_F_VIRTIO_NET_HDR for vhost-net (which may be
> vhoust-user-net). But we can simply recalculte these two flags inplace
> from hdev->features, and from net-client for
> VHOST_NET_F_VIRTIO_NET_HDR.
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
> ---
> hw/block/vhost-user-blk.c | 1 -
> hw/net/vhost_net.c | 16 ++++++++--------
> hw/scsi/vhost-scsi.c | 1 -
> hw/scsi/vhost-user-scsi.c | 1 -
> hw/virtio/vdpa-dev.c | 1 -
> hw/virtio/vhost-user.c | 19 +++++++++----------
> hw/virtio/virtio-hmp-cmds.c | 2 --
> hw/virtio/virtio-qmp.c | 2 --
> include/hw/virtio/vhost.h | 7 -------
> qapi/virtio.json | 3 ---
> 10 files changed, 17 insertions(+), 36 deletions(-)
>
> diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
> index c0cc5f6942..de7a810c93 100644
> --- a/hw/block/vhost-user-blk.c
> +++ b/hw/block/vhost-user-blk.c
> @@ -348,7 +348,6 @@ static int vhost_user_blk_connect(DeviceState *dev, Error **errp)
> s->dev.nvqs = s->num_queues;
> s->dev.vqs = s->vhost_vqs;
> s->dev.vq_index = 0;
> - s->dev.backend_features = 0;
>
> vhost_dev_set_config_notifier(&s->dev, &blk_ops);
>
> diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
> index 540492b37d..fcee279f0b 100644
> --- a/hw/net/vhost_net.c
> +++ b/hw/net/vhost_net.c
> @@ -53,7 +53,10 @@ int vhost_net_set_config(struct vhost_net *net, const uint8_t *data,
>
> void vhost_net_ack_features(struct vhost_net *net, uint64_t features)
> {
> - net->dev.acked_features = net->dev.backend_features;
> + net->dev.acked_features =
> + (qemu_has_vnet_hdr(net->nc) ? 0 : (1ULL << VHOST_NET_F_VIRTIO_NET_HDR))
> + | (net->dev.features & (1ULL << VHOST_USER_F_PROTOCOL_FEATURES));
> +
> vhost_ack_features(&net->dev, net->feature_bits, features);
> }
>
> @@ -256,12 +259,9 @@ struct vhost_net *vhost_net_init(VhostNetOptions *options)
> if (r < 0) {
> goto fail;
> }
> - net->dev.backend_features = qemu_has_vnet_hdr(options->net_backend)
> - ? 0 : (1ULL << VHOST_NET_F_VIRTIO_NET_HDR);
> net->backend = r;
> net->dev.protocol_features = 0;
> } else {
> - net->dev.backend_features = 0;
> net->dev.protocol_features = 0;
> net->backend = -1;
>
> @@ -281,10 +281,10 @@ struct vhost_net *vhost_net_init(VhostNetOptions *options)
> sizeof(struct virtio_net_hdr_mrg_rxbuf))) {
> net->dev.features &= ~(1ULL << VIRTIO_NET_F_MRG_RXBUF);
> }
> - if (~net->dev.features & net->dev.backend_features) {
> - fprintf(stderr, "vhost lacks feature mask 0x%" PRIx64
> - " for backend\n",
> - (uint64_t)(~net->dev.features & net->dev.backend_features));
> + if (!qemu_has_vnet_hdr(options->net_backend) &&
> + (~net->dev.features & (1ULL << VHOST_NET_F_VIRTIO_NET_HDR))) {
> + fprintf(stderr, "vhost lacks feature mask 0x%llx for backend\n",
> + ~net->dev.features & (1ULL << VHOST_NET_F_VIRTIO_NET_HDR));
> goto fail;
> }
> }
> diff --git a/hw/scsi/vhost-scsi.c b/hw/scsi/vhost-scsi.c
> index cdf405b0f8..d694a25fe2 100644
> --- a/hw/scsi/vhost-scsi.c
> +++ b/hw/scsi/vhost-scsi.c
> @@ -276,7 +276,6 @@ static void vhost_scsi_realize(DeviceState *dev, Error **errp)
> vqs = g_new0(struct vhost_virtqueue, vsc->dev.nvqs);
> vsc->dev.vqs = vqs;
> vsc->dev.vq_index = 0;
> - vsc->dev.backend_features = 0;
>
> ret = vhost_dev_init(&vsc->dev, (void *)(uintptr_t)vhostfd,
> VHOST_BACKEND_TYPE_KERNEL, 0, errp);
> diff --git a/hw/scsi/vhost-user-scsi.c b/hw/scsi/vhost-user-scsi.c
> index 25f2d894e7..0c80a271d8 100644
> --- a/hw/scsi/vhost-user-scsi.c
> +++ b/hw/scsi/vhost-user-scsi.c
> @@ -159,7 +159,6 @@ static int vhost_user_scsi_connect(DeviceState *dev, Error **errp)
> vsc->dev.nvqs = VIRTIO_SCSI_VQ_NUM_FIXED + vs->conf.num_queues;
> vsc->dev.vqs = s->vhost_vqs;
> vsc->dev.vq_index = 0;
> - vsc->dev.backend_features = 0;
>
> ret = vhost_dev_init(&vsc->dev, &s->vhost_user, VHOST_BACKEND_TYPE_USER, 0,
> errp);
> diff --git a/hw/virtio/vdpa-dev.c b/hw/virtio/vdpa-dev.c
> index d1da40afc8..3c0eed3e8e 100644
> --- a/hw/virtio/vdpa-dev.c
> +++ b/hw/virtio/vdpa-dev.c
> @@ -104,7 +104,6 @@ static void vhost_vdpa_device_realize(DeviceState *dev, Error **errp)
> v->dev.vqs = vqs;
> v->dev.vq_index = 0;
> v->dev.vq_index_end = v->dev.nvqs;
> - v->dev.backend_features = 0;
> v->started = false;
>
> ret = vhost_vdpa_get_iova_range(v->vhostfd, &iova_range);
> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> index 1b2879a90c..cf6f53801d 100644
> --- a/hw/virtio/vhost-user.c
> +++ b/hw/virtio/vhost-user.c
> @@ -1232,7 +1232,7 @@ static int vhost_user_set_vring_base(struct vhost_dev *dev,
>
> static bool vhost_user_set_vring_enable_supported(struct vhost_dev *dev)
> {
> - return virtio_has_feature(dev->backend_features,
> + return virtio_has_feature(dev->features,
> VHOST_USER_F_PROTOCOL_FEATURES);
> }
>
> @@ -1449,14 +1449,15 @@ static int vhost_user_set_features(struct vhost_dev *dev,
> int ret;
>
> /*
> - * We need to include any extra backend only feature bits that
> - * might be needed by our device. Currently this includes the
> - * VHOST_USER_F_PROTOCOL_FEATURES bit for enabling protocol
> - * features.
> + * Don't lose VHOST_USER_F_PROTOCOL_FEATURES, which is vhost-user
> + * specific.
> */
> - ret = vhost_user_set_u64(dev, VHOST_USER_SET_FEATURES,
> - features | dev->backend_features,
> - log_enabled);
> + if (virtio_has_feature(dev->features, VHOST_USER_F_PROTOCOL_FEATURES)) {
> + features |= 1ULL << VHOST_USER_F_PROTOCOL_FEATURES;
> + }
> +
> + ret = vhost_user_set_u64(dev, VHOST_USER_SET_FEATURES, features,
> + log_enabled);
>
> if (virtio_has_feature(dev->protocol_features,
> VHOST_USER_PROTOCOL_F_STATUS)) {
> @@ -2187,8 +2188,6 @@ static int vhost_user_backend_init(struct vhost_dev *dev, void *opaque,
> (dev->config_ops && dev->config_ops->vhost_dev_config_notifier);
> uint64_t protocol_features;
>
> - dev->backend_features |= 1ULL << VHOST_USER_F_PROTOCOL_FEATURES;
> -
> err = vhost_user_get_u64(dev, VHOST_USER_GET_PROTOCOL_FEATURES,
> &protocol_features);
> if (err < 0) {
> diff --git a/hw/virtio/virtio-hmp-cmds.c b/hw/virtio/virtio-hmp-cmds.c
> index 7d8677bcf0..024904915d 100644
> --- a/hw/virtio/virtio-hmp-cmds.c
> +++ b/hw/virtio/virtio-hmp-cmds.c
> @@ -175,8 +175,6 @@ void hmp_virtio_status(Monitor *mon, const QDict *qdict)
> hmp_virtio_dump_features(mon, s->vhost_dev->features);
> monitor_printf(mon, " Acked features:\n");
> hmp_virtio_dump_features(mon, s->vhost_dev->acked_features);
> - monitor_printf(mon, " Backend features:\n");
> - hmp_virtio_dump_features(mon, s->vhost_dev->backend_features);
> monitor_printf(mon, " Protocol features:\n");
> hmp_virtio_dump_protocols(mon, s->vhost_dev->protocol_features);
> }
> diff --git a/hw/virtio/virtio-qmp.c b/hw/virtio/virtio-qmp.c
> index 3b6377cf0d..e514a4797e 100644
> --- a/hw/virtio/virtio-qmp.c
> +++ b/hw/virtio/virtio-qmp.c
> @@ -788,8 +788,6 @@ VirtioStatus *qmp_x_query_virtio_status(const char *path, Error **errp)
> qmp_decode_features(vdev->device_id, hdev->features);
> status->vhost_dev->acked_features =
> qmp_decode_features(vdev->device_id, hdev->acked_features);
> - status->vhost_dev->backend_features =
> - qmp_decode_features(vdev->device_id, hdev->backend_features);
> status->vhost_dev->protocol_features =
> qmp_decode_protocols(hdev->protocol_features);
> status->vhost_dev->max_queues = hdev->max_queues;
> diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h
> index 66be6afc88..9f9dd2d46d 100644
> --- a/include/hw/virtio/vhost.h
> +++ b/include/hw/virtio/vhost.h
> @@ -100,16 +100,9 @@ struct vhost_dev {
> *
> * @features: available features provided by the backend
> * @acked_features: final negotiated features with front-end driver
> - *
> - * @backend_features: this is used in a couple of places to either
> - * store VHOST_USER_F_PROTOCOL_FEATURES to apply to
> - * VHOST_USER_SET_FEATURES or VHOST_NET_F_VIRTIO_NET_HDR. Its
> - * future use should be discouraged and the variable retired as
> - * its easy to confuse with the VirtIO backend_features.
> */
> uint64_t features;
> uint64_t acked_features;
> - uint64_t backend_features;
>
> /**
> * @protocol_features: is the vhost-user only feature set by
> diff --git a/qapi/virtio.json b/qapi/virtio.json
> index 9d652fe4a8..0aae77340d 100644
> --- a/qapi/virtio.json
> +++ b/qapi/virtio.json
> @@ -85,8 +85,6 @@
> #
> # @acked-features: vhost_dev acked_features
> #
> -# @backend-features: vhost_dev backend_features
> -#
> # @protocol-features: vhost_dev protocol_features
> #
> # @max-queues: vhost_dev max_queues
> @@ -106,7 +104,6 @@
> 'vq-index': 'int',
> 'features': 'VirtioDeviceFeatures',
> 'acked-features': 'VirtioDeviceFeatures',
> - 'backend-features': 'VirtioDeviceFeatures',
> 'protocol-features': 'VhostDeviceProtocols',
> 'max-queues': 'uint64',
> 'backend-cap': 'uint64',
> --
> 2.48.1
>
>