[RFC v2 09/10] vhost: Support VDUSE QUEUE_READY feature

Eugenio Pérez
2026-03-10T19:17:58Z

From: Super User <root@wsfd-advnetlab45.anl.eng.rdu2.dc.redhat.com>

Add support for the VDUSE_F_QUEUE_READY feature.

In VDUSE, the dataplane is enabled only after control virtqueue so the
device is fully configured in the destination of a live migration before
the dataplane starts. This message signals the VDUSE device when the
dataplane queues should be enabled.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
v2:
* Following latest comments on kernel series about VDUSE features, not
checking API version but only check if VDUSE_GET_FEATURES success.
---
lib/vhost/vduse.c | 72 +++++++++++++++++++++++++++++++++++++++++++++--
lib/vhost/vhost.h | 1 +
2 files changed, 71 insertions(+), 2 deletions(-)

diff --git a/lib/vhost/vduse.c b/lib/vhost/vduse.c
index 54fe6cf35bc6..f62cc3189076 100644
--- a/lib/vhost/vduse.c
+++ b/lib/vhost/vduse.c
@@ -39,12 +39,15 @@ static const char * const vduse_reqs_str[] = {
"VDUSE_SET_STATUS",
"VDUSE_UPDATE_IOTLB",
"VDUSE_SET_VQ_GROUP_ASID",
+ "VDUSE_SET_VQ_READY",
};

#define vduse_req_id_to_str(id) \
(id < RTE_DIM(vduse_reqs_str) ? \
vduse_reqs_str[id] : "Unknown")

+static const uint64_t supported_vduse_features = RTE_BIT64(VDUSE_F_QUEUE_READY);
+
static uint64_t vduse_vq_to_group(struct virtio_net *dev, struct vhost_virtqueue *vq)
{
if (dev->vduse_api_ver < 1)
@@ -500,6 +503,46 @@ vduse_events_handler(int fd, void *arg, int *close __rte_unused)
}
resp.result = VDUSE_REQ_RESULT_OK;
break;
+ case VDUSE_SET_VQ_READY:
+ if (!(dev->status & VIRTIO_DEVICE_STATUS_DRIVER_OK)) {
+ /*
+ * dev->notify_ops is NULL if !S_DRIVER_OK,
+ * vduse_device_start will check the queue readiness.
+ */
+ resp.result = VDUSE_REQ_RESULT_OK;
+ break;
+ }
+ if (!(dev->vduse_features & RTE_BIT64(VDUSE_F_QUEUE_READY))) {
+ VHOST_CONFIG_LOG(dev->ifname, ERR,
+ "Unexpected ready message with feature %d",
+ !!(dev->vduse_features &
+ RTE_BIT64(VDUSE_F_QUEUE_READY)));
+ resp.result = VDUSE_REQ_RESULT_FAILED;
+ break;
+ }
+
+ i = req.vq_ready.num;
+ vq = dev->virtqueue[i];
+ if (!dev->notify_ops || !dev->notify_ops->vring_state_changed) {
+ VHOST_CONFIG_LOG(dev->ifname, ERR,
+ "No ops->vring_state_changed");
+ resp.result = VDUSE_REQ_RESULT_FAILED;
+ break;
+ }
+
+ ret = dev->notify_ops->vring_state_changed(dev->vid, i,
+ req.vq_ready.ready);
+ VHOST_CONFIG_LOG(dev->ifname, INFO,
+ "\t\t VQ %d gets ready %d ok %d", i,
+ req.vq_ready.ready, ret);
+ if (ret != 0) {
+ resp.result = VDUSE_REQ_RESULT_FAILED;
+ break;
+ }
+
+ vq->enabled = req.vq_ready.ready;
+ resp.result = VDUSE_REQ_RESULT_OK;
+ break;
default:
resp.result = VDUSE_REQ_RESULT_FAILED;
break;
@@ -517,7 +560,8 @@ vduse_events_handler(int fd, void *arg, int *close __rte_unused)
if ((old_status ^ dev->status) & VIRTIO_DEVICE_STATUS_DRIVER_OK) {
if (dev->status & VIRTIO_DEVICE_STATUS_DRIVER_OK) {
/* Poll virtqueues ready states before starting device */
- ret = vduse_wait_for_virtqueues_ready(dev);
+ ret = dev->vduse_features & RTE_BIT64(VDUSE_F_QUEUE_READY) ? 0
+ : vduse_wait_for_virtqueues_ready(dev);
if (ret < 0) {
VHOST_CONFIG_LOG(dev->ifname, ERR,
"Failed to wait for virtqueues ready, aborting device start");
@@ -723,6 +767,26 @@ vduse_reconnect_start_device(struct virtio_net *dev)
return ret;
}

+/* If some error occurs just continue as if the kernel exposed no features */
+static uint64_t
+vduse_device_get_vduse_features(int control_fd, const char *log_name)
+{
+ uint64_t vduse_kernel_features;
+ int ret;
+
+ ret = ioctl(control_fd, VDUSE_GET_FEATURES, &vduse_kernel_features);
+ if (ret < 0) {
+ VHOST_CONFIG_LOG(log_name, INFO,
+ "Failed to get kernel VDUSE features, assuming not supported: %d(%s)",
+ errno, strerror(errno));
+ return 0;
+ }
+
+ VHOST_CONFIG_LOG(log_name, DEBUG, "Setting vhost kernel features: %lx",
+ vduse_kernel_features & supported_vduse_features);
+ return vduse_kernel_features & supported_vduse_features;
+}
+
int
vduse_device_create(const char *path, bool compliant_ol_flags, bool extbuf, bool linearbuf)
{
@@ -731,7 +795,7 @@ vduse_device_create(const char *path, bool compliant_ol_flags, bool extbuf, bool
struct virtio_net *dev;
struct virtio_net_config vnet_config = {{ 0 }};
uint64_t ver;
- uint64_t features;
+ uint64_t features, vduse_features = 0;
const char *name = path + strlen("/dev/vduse/");
bool reconnect = false;

@@ -815,6 +879,9 @@ vduse_device_create(const char *path, bool compliant_ol_flags, bool extbuf, bool
dev_config->ngroups = 2;
dev_config->nas = 2;
}
+
+ vduse_features = vduse_device_get_vduse_features(control_fd, name);
+ dev_config->vduse_features = vduse_features;
dev_config->config_size = sizeof(struct virtio_net_config);
memcpy(dev_config->config, &vnet_config, sizeof(vnet_config));

@@ -865,6 +932,7 @@ vduse_device_create(const char *path, bool compliant_ol_flags, bool extbuf, bool
dev->vduse_ctrl_fd = control_fd;
dev->vduse_dev_fd = dev_fd;
dev->vduse_api_ver = ver;
+ dev->vduse_features = vduse_features;

ret = vduse_reconnect_log_map(dev, !reconnect);
if (ret < 0)
diff --git a/lib/vhost/vhost.h b/lib/vhost/vhost.h
index 50b09da5ecf7..ce2e1a271c6f 100644
--- a/lib/vhost/vhost.h
+++ b/lib/vhost/vhost.h
@@ -533,6 +533,7 @@ struct __rte_cache_aligned virtio_net {
int vduse_ctrl_fd;
int vduse_dev_fd;
uint64_t vduse_api_ver;
+ uint64_t vduse_features;

struct vhost_virtqueue *cvq;

--
2.53.0