This commit implements datagram support for vhost/vsock by teaching
vhost to use the common virtio transport datagram functions.

If the virtio RX buffer is too small, then the transmission is
abandoned, the packet dropped, and EHOSTUNREACH is added to the socket's
error queue.

Signed-off-by: Bobby Eshleman <redacted>
---
 drivers/vhost/vsock.c    | 62 +++++++++++++++++++++++++++++++++++++++++++++---
 net/vmw_vsock/af_vsock.c |  5 +++-
 2 files changed, 63 insertions(+), 4 deletions(-)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index d5d6a3c3f273..da14260c6654 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c

@@ -8,6 +8,7 @@
  */
 #include <linux/miscdevice.h>
 #include <linux/atomic.h>
+#include <linux/errqueue.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
 #include <linux/vmalloc.h>

@@ -32,7 +33,8 @@
 enum {
 	VHOST_VSOCK_FEATURES = VHOST_FEATURES |
 			       (1ULL << VIRTIO_F_ACCESS_PLATFORM) |
-			       (1ULL << VIRTIO_VSOCK_F_SEQPACKET)
+			       (1ULL << VIRTIO_VSOCK_F_SEQPACKET) |
+			       (1ULL << VIRTIO_VSOCK_F_DGRAM)
 };
 
 enum {

@@ -56,6 +58,7 @@ struct vhost_vsock {
 	atomic_t queued_replies;
 
 	u32 guest_cid;
+	bool dgram_allow;
 	bool seqpacket_allow;
 };
 

@@ -86,6 +89,32 @@ static struct vhost_vsock *vhost_vsock_get(u32 guest_cid)
 	return NULL;
 }
 
+/* Claims ownership of the skb, do not free the skb after calling! */
+static void
+vhost_transport_error(struct sk_buff *skb, int err)
+{
+	struct sock_exterr_skb *serr;
+	struct sock *sk = skb->sk;
+	struct sk_buff *clone;
+
+	serr = SKB_EXT_ERR(skb);
+	memset(serr, 0, sizeof(*serr));
+	serr->ee.ee_errno = err;
+	serr->ee.ee_origin = SO_EE_ORIGIN_NONE;
+
+	clone = skb_clone(skb, GFP_KERNEL);

+
+	if (sock_queue_err_skb(sk, clone))
+		kfree_skb(clone);
+
+	sk->sk_err = err;
+	sk_error_report(sk);
+
+	kfree_skb(skb);
+}
+
 static void
 vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
 			    struct vhost_virtqueue *vq)

@@ -160,9 +189,15 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
 		hdr = virtio_vsock_hdr(skb);
 
 		/* If the packet is greater than the space available in the
-		 * buffer, we split it using multiple buffers.
+		 * buffer, we split it using multiple buffers for connectible
+		 * sockets and drop the packet for datagram sockets.
 		 */
 		if (payload_len > iov_len - sizeof(*hdr)) {
+			if (le16_to_cpu(hdr->type) == VIRTIO_VSOCK_TYPE_DGRAM) {
+				vhost_transport_error(skb, EHOSTUNREACH);
+				continue;
+			}
+
 			payload_len = iov_len - sizeof(*hdr);
 
 			/* As we are copying pieces of large packet's buffer to

@@ -394,6 +429,7 @@ static bool vhost_vsock_more_replies(struct vhost_vsock *vsock)
 	return val < vq->num;
 }
 
+static bool vhost_transport_dgram_allow(u32 cid, u32 port);
 static bool vhost_transport_seqpacket_allow(u32 remote_cid);
 
 static struct virtio_transport vhost_transport = {

@@ -410,7 +446,8 @@ static struct virtio_transport vhost_transport = {
 		.cancel_pkt               = vhost_transport_cancel_pkt,
 
 		.dgram_enqueue            = virtio_transport_dgram_enqueue,
-		.dgram_allow              = virtio_transport_dgram_allow,
+		.dgram_allow              = vhost_transport_dgram_allow,
+		.dgram_addr_init          = virtio_transport_dgram_addr_init,
 
 		.stream_enqueue           = virtio_transport_stream_enqueue,
 		.stream_dequeue           = virtio_transport_stream_dequeue,

@@ -443,6 +480,22 @@ static struct virtio_transport vhost_transport = {
 	.send_pkt = vhost_transport_send_pkt,
 };
 
+static bool vhost_transport_dgram_allow(u32 cid, u32 port)
+{
+	struct vhost_vsock *vsock;
+	bool dgram_allow = false;
+
+	rcu_read_lock();
+	vsock = vhost_vsock_get(cid);
+
+	if (vsock)
+		dgram_allow = vsock->dgram_allow;
+
+	rcu_read_unlock();
+
+	return dgram_allow;
+}
+
 static bool vhost_transport_seqpacket_allow(u32 remote_cid)
 {
 	struct vhost_vsock *vsock;

@@ -799,6 +852,9 @@ static int vhost_vsock_set_features(struct vhost_vsock *vsock, u64 features)
 	if (features & (1ULL << VIRTIO_VSOCK_F_SEQPACKET))
 		vsock->seqpacket_allow = true;
 
+	if (features & (1ULL << VIRTIO_VSOCK_F_DGRAM))
+		vsock->dgram_allow = true;
+
 	for (i = 0; i < ARRAY_SIZE(vsock->vqs); i++) {
 		vq = &vsock->vqs[i];
 		mutex_lock(&vq->mutex);

diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index e73f3b2c52f1..449ed63ac2b0 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c

@@ -1427,9 +1427,12 @@ int vsock_dgram_recvmsg(struct socket *sock, struct msghdr *msg,
 		return prot->recvmsg(sk, msg, len, flags, NULL);
 #endif
 
-	if (flags & MSG_OOB || flags & MSG_ERRQUEUE)
+	if (unlikely(flags & MSG_OOB))
 		return -EOPNOTSUPP;
 
+	if (unlikely(flags & MSG_ERRQUEUE))
+		return sock_recv_errqueue(sk, msg, len, SOL_VSOCK, 0);
+