Re: [RFC] vsock: add multiple transports support for dgram

[Jorgen Hansen <jhansen@vmware.com>]

> On 6 Apr 2021, at 20:31, Jiang Wang <jiang.wang@bytedance.com> wrote:
> 
> From: "jiang.wang" <jiang.wang@bytedance.com>
> 
> Currently, only VMCI supports dgram sockets. To supported
> nested VM use case, this patch removes transport_dgram and
> uses transport_g2h and transport_h2g for dgram too.

Could you provide some background for introducing this change - are you
looking at introducing datagrams for a different transport? VMCI datagrams
already support the nested use case, but if we need to support multiple datagram
transports we need to rework how we administer port assignment for datagrams.
One specific issue is that the vmci transport won’t receive any datagrams for a
port unless the datagram socket has already been assigned the vmci transport
and the port bound to the underlying VMCI device (see below for more details).


> The transport is assgined when sending every packet and
> receiving every packet on dgram sockets.

Is the intent that the same datagram socket can be used for sending packets both
In the host to guest, and the guest to directions? 

Also, as mentioned above the vSocket datagram needs to be bound to a port in the
VMCI transport before we can receive any datagrams on that port. This means that
vmci_transport_recv_dgram_cb won’t be called unless it is already associated with
a socket as the transport, and therefore we can’t delay the transport assignment to
that point.


> Signed-off-by: Jiang Wang <jiang.wang@bytedance.com>
> ---
> This patch is not tested. I don't have a VMWare testing
> environment. Could someone help me to test it? 
> 
> include/net/af_vsock.h         |  2 --
> net/vmw_vsock/af_vsock.c       | 63 +++++++++++++++++++++---------------------
> net/vmw_vsock/vmci_transport.c | 20 +++++++++-----
> 3 files changed, 45 insertions(+), 40 deletions(-)
> 
> diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
> index b1c717286993..aba241e0d202 100644
> --- a/include/net/af_vsock.h
> +++ b/include/net/af_vsock.h
> @@ -96,8 +96,6 @@ struct vsock_transport_send_notify_data {
> #define VSOCK_TRANSPORT_F_H2G		0x00000001
> /* Transport provides guest->host communication */
> #define VSOCK_TRANSPORT_F_G2H		0x00000002
> -/* Transport provides DGRAM communication */
> -#define VSOCK_TRANSPORT_F_DGRAM		0x00000004
> /* Transport provides local (loopback) communication */
> #define VSOCK_TRANSPORT_F_LOCAL		0x00000008
> 
> diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> index 92a72f0e0d94..7739ab2521a1 100644
> --- a/net/vmw_vsock/af_vsock.c
> +++ b/net/vmw_vsock/af_vsock.c
> @@ -449,8 +449,6 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk)
> 
> 	switch (sk->sk_type) {
> 	case SOCK_DGRAM:
> -		new_transport = transport_dgram;
> -		break;
> 	case SOCK_STREAM:
> 		if (vsock_use_local_transport(remote_cid))
> 			new_transport = transport_local;
> @@ -1096,7 +1094,6 @@ static int vsock_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
> 	struct sock *sk;
> 	struct vsock_sock *vsk;
> 	struct sockaddr_vm *remote_addr;
> -	const struct vsock_transport *transport;
> 
> 	if (msg->msg_flags & MSG_OOB)
> 		return -EOPNOTSUPP;
> @@ -1108,25 +1105,30 @@ static int vsock_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
> 
> 	lock_sock(sk);
> 
> -	transport = vsk->transport;
> -
> 	err = vsock_auto_bind(vsk);
> 	if (err)
> 		goto out;
> 
> -
> 	/* If the provided message contains an address, use that.  Otherwise
> 	 * fall back on the socket's remote handle (if it has been connected).
> 	 */
> 	if (msg->msg_name &&
> 	    vsock_addr_cast(msg->msg_name, msg->msg_namelen,
> 			    &remote_addr) == 0) {
> +		vsock_addr_init(&vsk->remote_addr, remote_addr->svm_cid,
> +			remote_addr->svm_port);
> +
> +		err = vsock_assign_transport(vsk, NULL);
> +		if (err) {
> +			err = -EINVAL;
> +			goto out;
> +		}
> +
> 		/* Ensure this address is of the right type and is a valid
> 		 * destination.
> 		 */
> -
> 		if (remote_addr->svm_cid == VMADDR_CID_ANY)
> -			remote_addr->svm_cid = transport->get_local_cid();
> +			remote_addr->svm_cid = vsk->transport->get_local_cid();
> 
> 		if (!vsock_addr_bound(remote_addr)) {
> 			err = -EINVAL;
> @@ -1136,7 +1138,7 @@ static int vsock_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
> 		remote_addr = &vsk->remote_addr;
> 
> 		if (remote_addr->svm_cid == VMADDR_CID_ANY)
> -			remote_addr->svm_cid = transport->get_local_cid();
> +			remote_addr->svm_cid = vsk->transport->get_local_cid();
> 
> 		/* XXX Should connect() or this function ensure remote_addr is
> 		 * bound?
> @@ -1150,13 +1152,13 @@ static int vsock_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
> 		goto out;
> 	}
> 
> -	if (!transport->dgram_allow(remote_addr->svm_cid,
> +	if (!vsk->transport->dgram_allow(remote_addr->svm_cid,
> 				    remote_addr->svm_port)) {
> 		err = -EINVAL;
> 		goto out;
> 	}
> 
> -	err = transport->dgram_enqueue(vsk, remote_addr, msg, len);
> +	err = vsk->transport->dgram_enqueue(vsk, remote_addr, msg, len);
> 
> out:
> 	release_sock(sk);
> @@ -1191,13 +1193,20 @@ static int vsock_dgram_connect(struct socket *sock,
> 	if (err)
> 		goto out;
> 
> +	memcpy(&vsk->remote_addr, remote_addr, sizeof(vsk->remote_addr));
> +
> +	err = vsock_assign_transport(vsk, NULL);
> +	if (err) {
> +		err = -EINVAL;
> +		goto out;
> +	}
> +
> 	if (!vsk->transport->dgram_allow(remote_addr->svm_cid,
> 					 remote_addr->svm_port)) {
> 		err = -EINVAL;
> 		goto out;
> 	}
> 
> -	memcpy(&vsk->remote_addr, remote_addr, sizeof(vsk->remote_addr));
> 	sock->state = SS_CONNECTED;
> 
> out:
> @@ -1209,6 +1218,16 @@ static int vsock_dgram_recvmsg(struct socket *sock, struct msghdr *msg,
> 			       size_t len, int flags)
> {
> 	struct vsock_sock *vsk = vsock_sk(sock->sk);
> +	long timeo;
> +
> +	timeo = sock_rcvtimeo(sock->sk, flags & MSG_DONTWAIT);
> +	do {
> +		if (vsk->transport)
> +			break;
> +	} while (timeo && !vsk->transport);
> +
> +	if (!vsk->transport)
> +		return -EAGAIN;
> 
> 	return vsk->transport->dgram_dequeue(vsk, msg, len, flags);
> }
> @@ -2055,14 +2074,6 @@ static int vsock_create(struct net *net, struct socket *sock,
> 
> 	vsk = vsock_sk(sk);
> 
> -	if (sock->type == SOCK_DGRAM) {
> -		ret = vsock_assign_transport(vsk, NULL);
> -		if (ret < 0) {
> -			sock_put(sk);
> -			return ret;
> -		}
> -	}
> -
> 	vsock_insert_unbound(vsk);
> 
> 	return 0;
> @@ -2182,7 +2193,7 @@ EXPORT_SYMBOL_GPL(vsock_core_get_transport);
> 
> int vsock_core_register(const struct vsock_transport *t, int features)
> {
> -	const struct vsock_transport *t_h2g, *t_g2h, *t_dgram, *t_local;
> +	const struct vsock_transport *t_h2g, *t_g2h, *t_local;
> 	int err = mutex_lock_interruptible(&vsock_register_mutex);
> 
> 	if (err)
> @@ -2190,7 +2201,6 @@ int vsock_core_register(const struct vsock_transport *t, int features)
> 
> 	t_h2g = transport_h2g;
> 	t_g2h = transport_g2h;
> -	t_dgram = transport_dgram;
> 	t_local = transport_local;
> 
> 	if (features & VSOCK_TRANSPORT_F_H2G) {
> @@ -2209,14 +2219,6 @@ int vsock_core_register(const struct vsock_transport *t, int features)
> 		t_g2h = t;
> 	}
> 
> -	if (features & VSOCK_TRANSPORT_F_DGRAM) {
> -		if (t_dgram) {
> -			err = -EBUSY;
> -			goto err_busy;
> -		}
> -		t_dgram = t;
> -	}
> -
> 	if (features & VSOCK_TRANSPORT_F_LOCAL) {
> 		if (t_local) {
> 			err = -EBUSY;
> @@ -2227,7 +2229,6 @@ int vsock_core_register(const struct vsock_transport *t, int features)
> 
> 	transport_h2g = t_h2g;
> 	transport_g2h = t_g2h;
> -	transport_dgram = t_dgram;
> 	transport_local = t_local;
> 
> err_busy:
> diff --git a/net/vmw_vsock/vmci_transport.c b/net/vmw_vsock/vmci_transport.c
> index 8b65323207db..42ea2a1c92ce 100644
> --- a/net/vmw_vsock/vmci_transport.c
> +++ b/net/vmw_vsock/vmci_transport.c
> @@ -613,6 +613,7 @@ static int vmci_transport_recv_dgram_cb(void *data, struct vmci_datagram *dg)
> 	size_t size;
> 	struct sk_buff *skb;
> 	struct vsock_sock *vsk;
> +	int err;
> 
> 	sk = (struct sock *)data;
> 
> @@ -629,6 +630,17 @@ static int vmci_transport_recv_dgram_cb(void *data, struct vmci_datagram *dg)
> 	if (!vmci_transport_allow_dgram(vsk, dg->src.context))
> 		return VMCI_ERROR_NO_ACCESS;
> 
> +	vsock_addr_init(&vsk->remote_addr, dg->src.context,
> +				dg->src.resource);
> +
> +	bh_lock_sock(sk);
> +	if (!sock_owned_by_user(sk)) {
> +		err = vsock_assign_transport(vsk, NULL);
> +		if (err)
> +			return err;
> +	}
> +	bh_unlock_sock(sk);
> +
> 	size = VMCI_DG_SIZE(dg);
> 
> 	/* Attach the packet to the socket's receive queue as an sk_buff. */
> @@ -2093,13 +2105,7 @@ static int __init vmci_transport_init(void)
> 		goto err_destroy_stream_handle;
> 	}
> 
> -	/* Register only with dgram feature, other features (H2G, G2H) will be
> -	 * registered when the first host or guest becomes active.
> -	 */
> -	err = vsock_core_register(&vmci_transport, VSOCK_TRANSPORT_F_DGRAM);
> -	if (err < 0)
> -		goto err_unsubscribe;
> -
> +	/* H2G, G2H will be registered when the first host or guest becomes active. */
> 	err = vmci_register_vsock_callback(vmci_vsock_transport_cb);
> 	if (err < 0)
> 		goto err_unregister;
> -- 
> 2.11.0
>