vhost: drop backend_features field
This field is mostly unused and sometimes confusing. We even have a TODO-like comment to drop it, the comment is removed in this commit. 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 vhost-user-net). But we can simply recalculate these two flags in place from hdev->features, and from net-client for VHOST_NET_F_VIRTIO_NET_HDR. Note: removing field from x-query-virtio-status result is incompatible change. We can do it because the command is unstable. Cc: devel@lists.libvirt.org Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> Acked-by: Markus Armbruster <armbru@redhat.com> Reviewed-by: Daniil Tatianin <d-tatianin@yandex-team.ru> Acked-by: Raphael Norwitz <raphael.s.norwitz@gmail.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Tested-by: Lei Yang <leiyang@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Message-Id: <20260420200339.708640-3-vsementsov@yandex-team.ru>
Vladimir Sementsov-Ogievskiy committed
Apr 20, 2026 at 23:03 UTC
1ee0bc0c9bf006a1ea9afeae67b6b7a0b57a4783
10 files changed
+22
-41
hw/block/vhost-user-blk.c
-1
@@ -348,7 +348,6 @@ static int vhost_user_blk_connect(DeviceState *dev, Error **errp)
348
s->dev.nvqs = s->num_queues;
349
s->dev.vqs = s->vhost_vqs;
350
s->dev.vq_index = 0;
351
- s->dev.backend_features = 0;
351
352
vhost_dev_set_config_notifier(&s->dev, &blk_ops);
353
hw/net/vhost_net.c
+14
-12
@@ -52,8 +52,14 @@ int vhost_net_set_config(struct vhost_net *net, const uint8_t *data,
52
53
void vhost_net_ack_features_ex(struct vhost_net *net, const uint64_t *features)
54
{
55
- virtio_features_copy(net->dev.acked_features_ex,
56
- net->dev.backend_features_ex);
55
+ virtio_features_clear(net->dev.acked_features_ex);
56
+ if (net->backend == -1) {
57
+ net->dev.acked_features =
58
+ net->dev.features & (1ULL << VHOST_USER_F_PROTOCOL_FEATURES);
59
+ } else if (!qemu_has_vnet_hdr(net->nc)) {
60
+ net->dev.acked_features = 1ULL << VHOST_NET_F_VIRTIO_NET_HDR;
61
+ }
62
+
63
vhost_ack_features_ex(&net->dev, net->feature_bits, features);
64
}
65
@@ -258,12 +264,9 @@ struct vhost_net *vhost_net_init(VhostNetOptions *options)
264
if (r < 0) {
265
goto fail;
266
}
261
- net->dev.backend_features = qemu_has_vnet_hdr(options->net_backend)
262
- ? 0 : (1ULL << VHOST_NET_F_VIRTIO_NET_HDR);
267
net->backend = r;
268
net->dev.protocol_features = 0;
269
} else {
266
- virtio_features_clear(net->dev.backend_features_ex);
270
net->dev.protocol_features = 0;
271
net->backend = -1;
272
@@ -284,13 +287,12 @@ struct vhost_net *vhost_net_init(VhostNetOptions *options)
287
net->dev.features &= ~(1ULL << VIRTIO_NET_F_MRG_RXBUF);
288
}
289
287
- if (virtio_features_andnot(missing_features,
288
- net->dev.backend_features_ex,
289
- net->dev.features_ex)) {
290
- fprintf(stderr, "vhost lacks feature mask 0x" VIRTIO_FEATURES_FMT
291
- " for backend\n", VIRTIO_FEATURES_PR(missing_features));
292
- goto fail;
293
- }
290
+ if (!qemu_has_vnet_hdr(options->net_backend) &&
291
+ (~net->dev.features & (1ULL << VHOST_NET_F_VIRTIO_NET_HDR))) {
292
+ fprintf(stderr, "vhost lacks feature mask 0x%llx for backend\n",
293
+ ~net->dev.features & (1ULL << VHOST_NET_F_VIRTIO_NET_HDR));
294
+ goto fail;
295
+ }
296
}
297
298
/* Set sane init value. Override when guest acks. */
hw/scsi/vhost-scsi.c
-1
@@ -275,7 +275,6 @@ static void vhost_scsi_realize(DeviceState *dev, Error **errp)
275
vqs = g_new0(struct vhost_virtqueue, vsc->dev.nvqs);
276
vsc->dev.vqs = vqs;
277
vsc->dev.vq_index = 0;
278
- vsc->dev.backend_features = 0;
278
279
ret = vhost_dev_init(&vsc->dev, (void *)(uintptr_t)vhostfd,
280
VHOST_BACKEND_TYPE_KERNEL, 0, errp);
hw/scsi/vhost-user-scsi.c
-1
@@ -159,7 +159,6 @@ static int vhost_user_scsi_connect(DeviceState *dev, Error **errp)
159
vsc->dev.nvqs = VIRTIO_SCSI_VQ_NUM_FIXED + vs->conf.num_queues;
160
vsc->dev.vqs = s->vhost_vqs;
161
vsc->dev.vq_index = 0;
162
- vsc->dev.backend_features = 0;
162
163
ret = vhost_dev_init(&vsc->dev, &s->vhost_user, VHOST_BACKEND_TYPE_USER, 0,
164
errp);
hw/virtio/vdpa-dev.c
-1
@@ -104,7 +104,6 @@ static void vhost_vdpa_device_realize(DeviceState *dev, Error **errp)
104
v->dev.vqs = vqs;
105
v->dev.vq_index = 0;
106
v->dev.vq_index_end = v->dev.nvqs;
107
- v->dev.backend_features = 0;
107
v->started = false;
108
109
ret = vhost_vdpa_get_iova_range(v->vhostfd, &iova_range);
hw/virtio/vhost-user.c
+8
-9
@@ -1465,14 +1465,15 @@ static int vhost_user_set_features(struct vhost_dev *dev,
1465
int ret;
1466
1467
/*
1468
- * We need to include any extra backend only feature bits that
1469
- * might be needed by our device. Currently this includes the
1470
- * VHOST_USER_F_PROTOCOL_FEATURES bit for enabling protocol
1471
- * features.
1468
+ * Don't lose VHOST_USER_F_PROTOCOL_FEATURES, which is vhost-user
1469
+ * specific.
1470
*/
1473
- ret = vhost_user_set_u64(dev, VHOST_USER_SET_FEATURES,
1474
- features | dev->backend_features,
1475
- log_enabled);
1471
+ if (virtio_has_feature(dev->features, VHOST_USER_F_PROTOCOL_FEATURES)) {
1472
+ features |= 1ULL << VHOST_USER_F_PROTOCOL_FEATURES;
1473
+ }
1474
+
1475
+ ret = vhost_user_set_u64(dev, VHOST_USER_SET_FEATURES, features,
1476
+ log_enabled);
1477
1478
if (virtio_has_feature(dev->protocol_features,
1479
VHOST_USER_PROTOCOL_F_STATUS)) {
@@ -2192,8 +2193,6 @@ static int vhost_user_backend_init(struct vhost_dev *dev, void *opaque,
2193
(dev->config_ops && dev->config_ops->vhost_dev_config_notifier);
2194
uint64_t protocol_features;
2195
2195
- dev->backend_features |= 1ULL << VHOST_USER_F_PROTOCOL_FEATURES;
2196
-
2196
err = vhost_user_get_u64(dev, VHOST_USER_GET_PROTOCOL_FEATURES,
2197
&protocol_features);
2198
if (err < 0) {
hw/virtio/virtio-hmp-cmds.c
-2
@@ -176,8 +176,6 @@ void hmp_virtio_status(Monitor *mon, const QDict *qdict)
176
hmp_virtio_dump_features(mon, s->vhost_dev->features);
177
monitor_printf(mon, " Acked features:\n");
178
hmp_virtio_dump_features(mon, s->vhost_dev->acked_features);
179
- monitor_printf(mon, " Backend features:\n");
180
- hmp_virtio_dump_features(mon, s->vhost_dev->backend_features);
179
monitor_printf(mon, " Protocol features:\n");
180
hmp_virtio_dump_protocols(mon, s->vhost_dev->protocol_features);
181
}
hw/virtio/virtio-qmp.c
-4
@@ -710,8 +710,6 @@ VirtioStatus *qmp_x_query_virtio_status(const char *path, Error **errp)
710
vdev->guest_features_ex);
711
status->host_features = qmp_decode_features(vdev->device_id,
712
vdev->host_features_ex);
713
- status->backend_features = qmp_decode_features(vdev->device_id,
714
- vdev->backend_features_ex);
713
714
switch (vdev->device_endian) {
715
case VIRTIO_DEVICE_ENDIAN_LITTLE:
@@ -752,8 +750,6 @@ VirtioStatus *qmp_x_query_virtio_status(const char *path, Error **errp)
750
qmp_decode_features(vdev->device_id, hdev->features_ex);
751
status->vhost_dev->acked_features =
752
qmp_decode_features(vdev->device_id, hdev->acked_features_ex);
755
- status->vhost_dev->backend_features =
756
- qmp_decode_features(vdev->device_id, hdev->backend_features_ex);
753
754
status->vhost_dev->protocol_features =
755
qmp_decode_protocols(hdev->protocol_features);
include/hw/virtio/vhost.h
-7
@@ -100,16 +100,9 @@ struct vhost_dev {
100
*
101
* @features: available features provided by the backend
102
* @acked_features: final negotiated features with front-end driver
103
- *
104
- * @backend_features: this is used in a couple of places to either
105
- * store VHOST_USER_F_PROTOCOL_FEATURES to apply to
106
- * VHOST_USER_SET_FEATURES or VHOST_NET_F_VIRTIO_NET_HDR. Its
107
- * future use should be discouraged and the variable retired as
108
- * its easy to confuse with the VirtIO backend_features.
103
*/
104
VIRTIO_DECLARE_FEATURES(features);
105
VIRTIO_DECLARE_FEATURES(acked_features);
112
- VIRTIO_DECLARE_FEATURES(backend_features);
106
107
/**
108
* @protocol_features: is the vhost-user only feature set by
qapi/virtio.json
-3
@@ -85,8 +85,6 @@
85
#
86
# @acked-features: vhost_dev acked_features
87
#
88
-# @backend-features: vhost_dev backend_features
89
-#
88
# @protocol-features: vhost_dev protocol_features
89
#
90
# @max-queues: vhost_dev max_queues
@@ -106,7 +104,6 @@
104
'vq-index': 'int',
105
'features': 'VirtioDeviceFeatures',
106
'acked-features': 'VirtioDeviceFeatures',
109
- 'backend-features': 'VirtioDeviceFeatures',
107
'protocol-features': 'VhostDeviceProtocols',
108
'max-queues': 'uint64',
109
'backend-cap': 'uint64',