the ones that do:
* VHOST_GET_FEATURES
+ * VHOST_GET_PROTOCOL_FEATURES
* VHOST_GET_VRING_BASE
There are several messages that the master sends with file descriptors passed
If Master is unable to send the full message or receives a wrong reply it will
close the connection. An optional reconnection mechanism can be implemented.
+Any protocol extensions are gated by protocol feature bits,
+which allows full backwards compatibility on both master
+and slave.
+As older slaves don't support negotiating protocol features,
+a feature bit was dedicated for this purpose:
+#define VHOST_USER_F_PROTOCOL_FEATURES 30
+
Message types
-------------
Slave payload: u64
Get from the underlying vhost implementation the features bitmask.
+ Feature bit VHOST_USER_F_PROTOCOL_FEATURES signals slave support for
+ VHOST_USER_GET_PROTOCOL_FEATURES and VHOST_USER_SET_PROTOCOL_FEATURES.
* VHOST_USER_SET_FEATURES
Master payload: u64
Enable features in the underlying vhost implementation using a bitmask.
+ Feature bit VHOST_USER_F_PROTOCOL_FEATURES signals slave support for
+ VHOST_USER_GET_PROTOCOL_FEATURES and VHOST_USER_SET_PROTOCOL_FEATURES.
+
+ * VHOST_USER_GET_PROTOCOL_FEATURES
+
+ Id: 15
+ Equivalent ioctl: VHOST_GET_FEATURES
+ Master payload: N/A
+ Slave payload: u64
+
+ Get the protocol feature bitmask from the underlying vhost implementation.
+ Only legal if feature bit VHOST_USER_F_PROTOCOL_FEATURES is present in
+ VHOST_USER_GET_FEATURES.
+ Note: slave that reported VHOST_USER_F_PROTOCOL_FEATURES must support
+ this message even before VHOST_USER_SET_FEATURES was called.
+
+ * VHOST_USER_SET_PROTOCOL_FEATURES
+
+ Id: 16
+ Ioctl: VHOST_SET_FEATURES
+ Master payload: u64
+
+ Enable protocol features in the underlying vhost implementation.
+ Only legal if feature bit VHOST_USER_F_PROTOCOL_FEATURES is present in
+ VHOST_USER_GET_FEATURES.
+ Note: slave that reported VHOST_USER_F_PROTOCOL_FEATURES must support
+ this message even before VHOST_USER_SET_FEATURES was called.
* VHOST_USER_SET_OWNER
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;
}
net->nc = options->net_backend;
#include <linux/vhost.h>
#define VHOST_MEMORY_MAX_NREGIONS 8
+#define VHOST_USER_F_PROTOCOL_FEATURES 30
+#define VHOST_USER_PROTOCOL_FEATURE_MASK 0x0ULL
typedef enum VhostUserRequest {
VHOST_USER_NONE = 0,
VHOST_USER_SET_VRING_KICK = 12,
VHOST_USER_SET_VRING_CALL = 13,
VHOST_USER_SET_VRING_ERR = 14,
+ VHOST_USER_GET_PROTOCOL_FEATURES = 15,
+ VHOST_USER_SET_PROTOCOL_FEATURES = 16,
VHOST_USER_MAX
} VhostUserRequest;
switch (msg_request) {
case VHOST_USER_GET_FEATURES:
+ case VHOST_USER_GET_PROTOCOL_FEATURES:
need_reply = 1;
break;
case VHOST_USER_SET_FEATURES:
case VHOST_USER_SET_LOG_BASE:
+ case VHOST_USER_SET_PROTOCOL_FEATURES:
msg.u64 = *((__u64 *) arg);
msg.size = sizeof(m.u64);
break;
switch (msg_request) {
case VHOST_USER_GET_FEATURES:
+ case VHOST_USER_GET_PROTOCOL_FEATURES:
if (msg.size != sizeof(m.u64)) {
error_report("Received bad msg size.");
return -1;
static int vhost_user_init(struct vhost_dev *dev, void *opaque)
{
+ unsigned long long features;
+ int err;
+
assert(dev->vhost_ops->backend_type == VHOST_BACKEND_TYPE_USER);
dev->opaque = opaque;
+ err = vhost_user_call(dev, VHOST_USER_GET_FEATURES, &features);
+ if (err < 0) {
+ return err;
+ }
+
+ if (virtio_has_feature(features, VHOST_USER_F_PROTOCOL_FEATURES)) {
+ dev->backend_features |= 1ULL << VHOST_USER_F_PROTOCOL_FEATURES;
+
+ err = vhost_user_call(dev, VHOST_USER_GET_PROTOCOL_FEATURES, &features);
+ if (err < 0) {
+ return err;
+ }
+
+ dev->protocol_features = features & VHOST_USER_PROTOCOL_FEATURE_MASK;
+ err = vhost_user_call(dev, VHOST_USER_SET_PROTOCOL_FEATURES,
+ &dev->protocol_features);
+ if (err < 0) {
+ return err;
+ }
+ }
+
return 0;
}
unsigned long long features;
unsigned long long acked_features;
unsigned long long backend_features;
+ unsigned long long protocol_features;
bool started;
bool log_enabled;
unsigned long long log_size;