Subject: Re: [PATCH RFC net-next v4 3/8] vsock: support multi-transport datagrams

From: Bobby Eshleman <[email-masked]>
Date: Fri, 23 Jun 2023 02:50:01 +0000

On Thu, Jun 22, 2023 at 05:19:08PM +0200, Stefano Garzarella wrote:
> On Sat, Jun 10, 2023 at 12:58:30AM +0000, Bobby Eshleman wrote:
> > This patch adds support for multi-transport datagrams.
> > 
> > This includes:
> > - Per-packet lookup of transports when using sendto(sockaddr_vm)
> > - Selecting H2G or G2H transport using VMADDR_FLAG_TO_HOST and CID in
> >  sockaddr_vm
> > 
> > To preserve backwards compatibility with VMCI, some important changes
> > were made. The "transport_dgram" / VSOCK_TRANSPORT_F_DGRAM is changed to
> > be used for dgrams iff there is not yet a g2h or h2g transport that has
> 
> s/iff/if
> 
> > been registered that can transmit the packet. If there is a g2h/h2g
> > transport for that remote address, then that transport will be used and
> > not "transport_dgram". This essentially makes "transport_dgram" a
> > fallback transport for when h2g/g2h has not yet gone online, which
> > appears to be the exact use case for VMCI.
> > 
> > This design makes sense, because there is no reason that the
> > transport_{g2h,h2g} cannot also service datagrams, which makes the role
> > of transport_dgram difficult to understand outside of the VMCI context.
> > 
> > The logic around "transport_dgram" had to be retained to prevent
> > breaking VMCI:
> > 
> > 1) VMCI datagrams appear to function outside of the h2g/g2h
> >   paradigm. When the vmci transport becomes online, it registers itself
> >   with the DGRAM feature, but not H2G/G2H. Only later when the
> >   transport has more information about its environment does it register
> >   H2G or G2H. In the case that a datagram socket becomes active
> >   after DGRAM registration but before G2H/H2G registration, the
> >   "transport_dgram" transport needs to be used.
> 
> IIRC we did this, because at that time only VMCI supported DGRAM. Now that
> there are more transports, maybe DGRAM can follow the h2g/g2h paradigm.
> 

Totally makes sense. I'll add the detail above that the prior design was
a result of chronology.

> > 
> > 2) VMCI seems to require special message be sent by the transport when a
> >   datagram socket calls bind(). Under the h2g/g2h model, the transport
> >   is selected using the remote_addr which is set by connect(). At
> >   bind time there is no remote_addr because often no connect() has been
> >   called yet: the transport is null. Therefore, with a null transport
> >   there doesn't seem to be any good way for a datagram socket a tell the
> >   VMCI transport that it has just had bind() called upon it.
> 
> @Vishnu, @Bryan do you think we can avoid this in some way?
> 
> > 
> > Only transports with a special datagram fallback use-case such as VMCI
> > need to register VSOCK_TRANSPORT_F_DGRAM.
> 
> Maybe we should rename it in VSOCK_TRANSPORT_F_DGRAM_FALLBACK or
> something like that.
> 
> In any case, we definitely need to update the comment in
> include/net/af_vsock.h on top of VSOCK_TRANSPORT_F_DGRAM mentioning
> this.
> 

Agreed. I'll rename to VSOCK_TRANSPORT_F_DGRAM_FALLBACK, unless we find
there is a better way altogether.

> > 
> > Signed-off-by: Bobby Eshleman <[email-masked]>
> > ---
> > drivers/vhost/vsock.c                   |  1 -
> > include/linux/virtio_vsock.h            |  2 -
> > net/vmw_vsock/af_vsock.c                | 78 +++++++++++++++++++++++++--------
> > net/vmw_vsock/hyperv_transport.c        |  6 ---
> > net/vmw_vsock/virtio_transport.c        |  1 -
> > net/vmw_vsock/virtio_transport_common.c |  7 ---
> > net/vmw_vsock/vsock_loopback.c          |  1 -
> > 7 files changed, 60 insertions(+), 36 deletions(-)
> > 
> > diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> > index c8201c070b4b..8f0082da5e70 100644
> > --- a/drivers/vhost/vsock.c
> > +++ b/drivers/vhost/vsock.c
> > @@ -410,7 +410,6 @@ static struct virtio_transport vhost_transport = {
> > 		.cancel_pkt               = vhost_transport_cancel_pkt,
> > 
> > 		.dgram_enqueue            = virtio_transport_dgram_enqueue,
> > -		.dgram_bind               = virtio_transport_dgram_bind,
> > 		.dgram_allow              = virtio_transport_dgram_allow,
> > 		.dgram_get_cid		  = virtio_transport_dgram_get_cid,
> > 		.dgram_get_port		  = virtio_transport_dgram_get_port,
> > diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
> > index 23521a318cf0..73afa09f4585 100644
> > --- a/include/linux/virtio_vsock.h
> > +++ b/include/linux/virtio_vsock.h
> > @@ -216,8 +216,6 @@ void virtio_transport_notify_buffer_size(struct vsock_sock *vsk, u64 *val);
> > u64 virtio_transport_stream_rcvhiwat(struct vsock_sock *vsk);
> > bool virtio_transport_stream_is_active(struct vsock_sock *vsk);
> > bool virtio_transport_stream_allow(u32 cid, u32 port);
> > -int virtio_transport_dgram_bind(struct vsock_sock *vsk,
> > -				struct sockaddr_vm *addr);
> > bool virtio_transport_dgram_allow(u32 cid, u32 port);
> > int virtio_transport_dgram_get_cid(struct sk_buff *skb, unsigned int *cid);
> > int virtio_transport_dgram_get_port(struct sk_buff *skb, unsigned int *port);
> > diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> > index 74358f0b47fa..ef86765f3765 100644
> > --- a/net/vmw_vsock/af_vsock.c
> > +++ b/net/vmw_vsock/af_vsock.c
> > @@ -438,6 +438,18 @@ vsock_connectible_lookup_transport(unsigned int cid, __u8 flags)
> > 	return transport;
> > }
> > 
> > +static const struct vsock_transport *
> > +vsock_dgram_lookup_transport(unsigned int cid, __u8 flags)
> > +{
> > +	const struct vsock_transport *transport;
> > +
> > +	transport = vsock_connectible_lookup_transport(cid, flags);
> > +	if (transport)
> > +		return transport;
> > +
> > +	return transport_dgram;
> > +}
> > +
> > /* Assign a transport to a socket and call the .init transport callback.
> >  *
> >  * Note: for connection oriented socket this must be called when vsk->remote_addr
> > @@ -474,7 +486,8 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk)
> > 
> > 	switch (sk->sk_type) {
> > 	case SOCK_DGRAM:
> > -		new_transport = transport_dgram;
> > +		new_transport = vsock_dgram_lookup_transport(remote_cid,
> > +							     remote_flags);
> > 		break;
> > 	case SOCK_STREAM:
> > 	case SOCK_SEQPACKET:
> > @@ -691,6 +704,9 @@ static int __vsock_bind_connectible(struct vsock_sock *vsk,
> > static int __vsock_bind_dgram(struct vsock_sock *vsk,
> > 			      struct sockaddr_vm *addr)
> > {
> > +	if (!vsk->transport || !vsk->transport->dgram_bind)
> > +		return -EINVAL;
> > +
> > 	return vsk->transport->dgram_bind(vsk, addr);
> > }
> > 
> > @@ -1172,19 +1188,24 @@ 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) {
> > +		transport = vsock_dgram_lookup_transport(remote_addr->svm_cid,
> > +							 remote_addr->svm_flags);
> > +		if (!transport) {
> > +			err = -EINVAL;
> > +			goto out;
> > +		}
> > +
> > +		if (!try_module_get(transport->module)) {
> > +			err = -ENODEV;
> > +			goto out;
> > +		}
> > +
> > 		/* Ensure this address is of the right type and is a valid
> > 		 * destination.
> > 		 */
> > @@ -1193,11 +1214,27 @@ static int vsock_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
> > 			remote_addr->svm_cid = transport->get_local_cid();
> > 
> 
> From here ...
> 
> > 		if (!vsock_addr_bound(remote_addr)) {
> > +			module_put(transport->module);
> > +			err = -EINVAL;
> > +			goto out;
> > +		}
> > +
> > +		if (!transport->dgram_allow(remote_addr->svm_cid,
> > +					    remote_addr->svm_port)) {
> > +			module_put(transport->module);
> > 			err = -EINVAL;
> > 			goto out;
> > 		}
> > +
> > +		err = transport->dgram_enqueue(vsk, remote_addr, msg, len);
> 
> ... to here, looks like duplicate code, can we get it out of the if block?
> 

Yes, I think using something like this:

[...]
	bool module_got = false;

[...]
		if (!try_module_get(transport->module)) {
			err = -ENODEV;
			goto out;
		}
		module_got = true;

[...]

out:
	if (likely(transport && !err && module_got))
		module_put(transport->module)

> > +		module_put(transport->module);
> > 	} else if (sock->state == SS_CONNECTED) {
> > 		remote_addr = &vsk->remote_addr;
> > +		transport = vsk->transport;
> > +
> > +		err = vsock_auto_bind(vsk);
> > +		if (err)
> > +			goto out;
> > 
> > 		if (remote_addr->svm_cid == VMADDR_CID_ANY)
> > 			remote_addr->svm_cid = transport->get_local_cid();
> > @@ -1205,23 +1242,23 @@ static int vsock_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
> > 		/* XXX Should connect() or this function ensure remote_addr is
> > 		 * bound?
> > 		 */
> > -		if (!vsock_addr_bound(&vsk->remote_addr)) {
> > +		if (!vsock_addr_bound(remote_addr)) {
> > 			err = -EINVAL;
> > 			goto out;
> > 		}
> > -	} else {
> > -		err = -EINVAL;
> > -		goto out;
> > -	}
> > 
> > -	if (!transport->dgram_allow(remote_addr->svm_cid,
> > -				    remote_addr->svm_port)) {
> > +		if (!transport->dgram_allow(remote_addr->svm_cid,
> > +					    remote_addr->svm_port)) {
> > +			err = -EINVAL;
> > +			goto out;
> > +		}
> > +
> > +		err = transport->dgram_enqueue(vsk, remote_addr, msg, len);
> > +	} else {
> > 		err = -EINVAL;
> > 		goto out;
> > 	}
> > 
> > -	err = transport->dgram_enqueue(vsk, remote_addr, msg, len);
> > -
> > out:
> > 	release_sock(sk);
> > 	return err;
> > @@ -1255,13 +1292,18 @@ 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)
> > +		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;
> > 
> > 	/* sock map disallows redirection of non-TCP sockets with sk_state !=
> > diff --git a/net/vmw_vsock/hyperv_transport.c b/net/vmw_vsock/hyperv_transport.c
> > index ff6e87e25fa0..c00bc5da769a 100644
> > --- a/net/vmw_vsock/hyperv_transport.c
> > +++ b/net/vmw_vsock/hyperv_transport.c
> > @@ -551,11 +551,6 @@ static void hvs_destruct(struct vsock_sock *vsk)
> > 	kfree(hvs);
> > }
> > 
> > -static int hvs_dgram_bind(struct vsock_sock *vsk, struct sockaddr_vm *addr)
> > -{
> > -	return -EOPNOTSUPP;
> > -}
> > -
> > static int hvs_dgram_get_cid(struct sk_buff *skb, unsigned int *cid)
> > {
> > 	return -EOPNOTSUPP;
> > @@ -841,7 +836,6 @@ static struct vsock_transport hvs_transport = {
> > 	.connect                  = hvs_connect,
> > 	.shutdown                 = hvs_shutdown,
> > 
> > -	.dgram_bind               = hvs_dgram_bind,
> > 	.dgram_get_cid		  = hvs_dgram_get_cid,
> > 	.dgram_get_port		  = hvs_dgram_get_port,
> > 	.dgram_get_length	  = hvs_dgram_get_length,
> > diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
> > index 5763cdf13804..1b7843a7779a 100644
> > --- a/net/vmw_vsock/virtio_transport.c
> > +++ b/net/vmw_vsock/virtio_transport.c
> > @@ -428,7 +428,6 @@ static struct virtio_transport virtio_transport = {
> > 		.shutdown                 = virtio_transport_shutdown,
> > 		.cancel_pkt               = virtio_transport_cancel_pkt,
> > 
> > -		.dgram_bind               = virtio_transport_dgram_bind,
> > 		.dgram_enqueue            = virtio_transport_dgram_enqueue,
> > 		.dgram_allow              = virtio_transport_dgram_allow,
> > 		.dgram_get_cid		  = virtio_transport_dgram_get_cid,
> > diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> > index e6903c719964..d5a3c8efe84b 100644
> > --- a/net/vmw_vsock/virtio_transport_common.c
> > +++ b/net/vmw_vsock/virtio_transport_common.c
> > @@ -790,13 +790,6 @@ bool virtio_transport_stream_allow(u32 cid, u32 port)
> > }
> > EXPORT_SYMBOL_GPL(virtio_transport_stream_allow);
> > 
> > -int virtio_transport_dgram_bind(struct vsock_sock *vsk,
> > -				struct sockaddr_vm *addr)
> > -{
> > -	return -EOPNOTSUPP;
> > -}
> > -EXPORT_SYMBOL_GPL(virtio_transport_dgram_bind);
> > -
> > int virtio_transport_dgram_get_cid(struct sk_buff *skb, unsigned int *cid)
> > {
> > 	return -EOPNOTSUPP;
> > diff --git a/net/vmw_vsock/vsock_loopback.c b/net/vmw_vsock/vsock_loopback.c
> > index 2f3cabc79ee5..e9de45a26fbd 100644
> > --- a/net/vmw_vsock/vsock_loopback.c
> > +++ b/net/vmw_vsock/vsock_loopback.c
> > @@ -61,7 +61,6 @@ static struct virtio_transport loopback_transport = {
> > 		.shutdown                 = virtio_transport_shutdown,
> > 		.cancel_pkt               = vsock_loopback_cancel_pkt,
> > 
> > -		.dgram_bind               = virtio_transport_dgram_bind,
> > 		.dgram_enqueue            = virtio_transport_dgram_enqueue,
> > 		.dgram_allow              = virtio_transport_dgram_allow,
> > 		.dgram_get_cid		  = virtio_transport_dgram_get_cid,
> > 
> > -- 
> > 2.30.2
> > 
> 
> The rest LGTM!
> 
> Stefano

Thanks,
Bobby