Re: [PATCH RFC net-next v5 11/14] vhost/vsock: implement datagram support

Bobby Eshleman
2023-08-02T19:28:31Z

On Wed, Jul 26, 2023 at 02:40:22PM -0400, Michael S. Tsirkin wrote:
> On Wed, Jul 19, 2023 at 12:50:15AM +0000, Bobby Eshleman wrote:
> > 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 <bobby.eshleman@bytedance.com>
>
> EHOSTUNREACH?
>
>
> > ---
> > 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 (!clone)
> > + return;
> > +
> > + 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.
> > */
>
> won't this break things like recently proposed zerocopy?
> I think splitup has to be supported for all types.
>

Could you elaborate? Is there something about zerocopy that would
prohibit the transport from dropping a datagram?

>
> > 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);
> > +
> > transport = vsk->transport;
> >
> > /* Retrieve the head sk_buff from the socket's receive queue. */
> >
> > --
> > 2.30.2
>
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