Re: [PATCH RFC net-next v5 03/14] af_vsock: support multi-transport datagrams

[Arseniy Krasnov <oxffffaa@gmail.com>]

On 19.07.2023 03:50, 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
> - rename VSOCK_TRANSPORT_F_DGRAM to VSOCK_TRANSPORT_F_DGRAM_FALLBACK
> - connect() now assigns the transport for (similar to connectible
>   sockets)
> 
> To preserve backwards compatibility with VMCI, some important changes
> are made. The "transport_dgram" / VSOCK_TRANSPORT_F_DGRAM is changed to
> be used for dgrams only if there is not yet a g2h or h2g transport that
> has 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, and so it
> is renamed "transport_dgram_fallback". VMCI implements this transport.
> 
> The logic around "transport_dgram" needs to be retained to prevent
> breaking VMCI:
> 
> 1) VMCI datagrams existed prior to h2g/g2h and so operate under a
>    different paradigm. When the vmci transport comes 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 is created after
>    VSOCK_TRANSPORT_F_DGRAM registration but before G2H/H2G registration,
>    the "transport_dgram" transport is the only registered transport and so
>    needs to be used.
> 
> 2) VMCI seems to require a 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 to tell the
>    VMCI transport that it has just had bind() called upon it.
> 
> With the new fallback logic, after H2G/G2H comes online the socket layer
> will access the VMCI transport via transport_{h2g,g2h}. Prior to H2G/G2H
> coming online, the socket layer will access the VMCI transport via
> "transport_dgram_fallback".
> 
> Only transports with a special datagram fallback use-case such as VMCI
> need to register VSOCK_TRANSPORT_F_DGRAM_FALLBACK.
> 
> Signed-off-by: Bobby Eshleman <bobby.eshleman@bytedance.com>
> ---
>  drivers/vhost/vsock.c                   |  1 -
>  include/linux/virtio_vsock.h            |  2 --
>  include/net/af_vsock.h                  | 10 +++---
>  net/vmw_vsock/af_vsock.c                | 64 ++++++++++++++++++++++++++-------
>  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/vmci_transport.c          |  2 +-
>  net/vmw_vsock/vsock_loopback.c          |  1 -
>  9 files changed, 58 insertions(+), 36 deletions(-)
> 
> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> index ae8891598a48..d5d6a3c3f273 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,
>  
>  		.stream_enqueue           = virtio_transport_stream_enqueue,
> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
> index 18cbe8d37fca..7632552bee58 100644
> --- a/include/linux/virtio_vsock.h
> +++ b/include/linux/virtio_vsock.h
> @@ -211,8 +211,6 @@ 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_connect(struct vsock_sock *vsk);
> diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
> index 305d57502e89..f6a0ca9d7c3e 100644
> --- a/include/net/af_vsock.h
> +++ b/include/net/af_vsock.h
> @@ -96,13 +96,13 @@ struct vsock_transport_send_notify_data {
>  
>  /* Transport features flags */
>  /* Transport provides host->guest communication */
> -#define VSOCK_TRANSPORT_F_H2G		0x00000001
> +#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
> +#define VSOCK_TRANSPORT_F_G2H			0x00000002
> +/* Transport provides fallback for DGRAM communication */
> +#define VSOCK_TRANSPORT_F_DGRAM_FALLBACK	0x00000004
>  /* Transport provides local (loopback) communication */
> -#define VSOCK_TRANSPORT_F_LOCAL		0x00000008
> +#define VSOCK_TRANSPORT_F_LOCAL			0x00000008
>  
>  struct vsock_transport {
>  	struct module *module;
> diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> index ae5ac5531d96..26c97b33d55a 100644
> --- a/net/vmw_vsock/af_vsock.c
> +++ b/net/vmw_vsock/af_vsock.c
> @@ -139,8 +139,8 @@ struct proto vsock_proto = {
>  static const struct vsock_transport *transport_h2g;
>  /* Transport used for guest->host communication */
>  static const struct vsock_transport *transport_g2h;
> -/* Transport used for DGRAM communication */
> -static const struct vsock_transport *transport_dgram;
> +/* Transport used as a fallback for DGRAM communication */
> +static const struct vsock_transport *transport_dgram_fallback;
>  /* Transport used for local communication */
>  static const struct vsock_transport *transport_local;
>  static DEFINE_MUTEX(vsock_register_mutex);
> @@ -439,6 +439,18 @@ 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_fallback;
> +}
> +
>  /* 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
> @@ -475,7 +487,8 @@ 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);

I'm a little bit confused about this: 
1) Let's create SOCK_DGRAM socket using vsock_create()
2) for SOCK_DGRAM it calls 'vsock_assign_transport()' and we go here, remote_cid == -1
3) I guess 'vsock_dgram_lookup_transport()' calls logic from 0002 and returns h2g for such remote cid, which is not
   correct I think...

Please correct me if i'm wrong

Thanks, Arseniy

>  		break;
>  	case SOCK_STREAM:
>  	case SOCK_SEQPACKET:
> @@ -692,6 +705,9 @@ 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);
>  }
>  
> @@ -1162,6 +1178,7 @@ static int vsock_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
>  	struct vsock_sock *vsk;
>  	struct sockaddr_vm *remote_addr;
>  	const struct vsock_transport *transport;
> +	bool module_got = false;
>  
>  	if (msg->msg_flags & MSG_OOB)
>  		return -EOPNOTSUPP;
> @@ -1173,19 +1190,34 @@ 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;
> +		}
> +
> +		/* When looking up a transport dynamically and acquiring a
> +		 * reference on the module, we need to remember to release the
> +		 * reference later.
> +		 */
> +		module_got = true;
> +
>  		/* Ensure this address is of the right type and is a valid
>  		 * destination.
>  		 */
> @@ -1200,6 +1232,7 @@ static int vsock_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
>  	} else if (sock->state == SS_CONNECTED) {
>  		remote_addr = &vsk->remote_addr;
>  
> +		transport = vsk->transport;
>  		if (remote_addr->svm_cid == VMADDR_CID_ANY)
>  			remote_addr->svm_cid = transport->get_local_cid();
>  
> @@ -1224,6 +1257,8 @@ static int vsock_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
>  	err = transport->dgram_enqueue(vsk, remote_addr, msg, len);
>  
>  out:
> +	if (module_got)
> +		module_put(transport->module);
>  	release_sock(sk);
>  	return err;
>  }
> @@ -1256,13 +1291,18 @@ 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 !=
> @@ -2487,7 +2527,7 @@ int vsock_core_register(const struct vsock_transport *t, int features)
>  
>  	t_h2g = transport_h2g;
>  	t_g2h = transport_g2h;
> -	t_dgram = transport_dgram;
> +	t_dgram = transport_dgram_fallback;
>  	t_local = transport_local;
>  
>  	if (features & VSOCK_TRANSPORT_F_H2G) {
> @@ -2506,7 +2546,7 @@ int vsock_core_register(const struct vsock_transport *t, int features)
>  		t_g2h = t;
>  	}
>  
> -	if (features & VSOCK_TRANSPORT_F_DGRAM) {
> +	if (features & VSOCK_TRANSPORT_F_DGRAM_FALLBACK) {
>  		if (t_dgram) {
>  			err = -EBUSY;
>  			goto err_busy;
> @@ -2524,7 +2564,7 @@ int vsock_core_register(const struct vsock_transport *t, int features)
>  
>  	transport_h2g = t_h2g;
>  	transport_g2h = t_g2h;
> -	transport_dgram = t_dgram;
> +	transport_dgram_fallback = t_dgram;
>  	transport_local = t_local;
>  
>  err_busy:
> @@ -2543,8 +2583,8 @@ void vsock_core_unregister(const struct vsock_transport *t)
>  	if (transport_g2h == t)
>  		transport_g2h = NULL;
>  
> -	if (transport_dgram == t)
> -		transport_dgram = NULL;
> +	if (transport_dgram_fallback == t)
> +		transport_dgram_fallback = NULL;
>  
>  	if (transport_local == t)
>  		transport_local = NULL;
> diff --git a/net/vmw_vsock/hyperv_transport.c b/net/vmw_vsock/hyperv_transport.c
> index 7f1ea434656d..c29000f2612a 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_enqueue(struct vsock_sock *vsk,
>  			     struct sockaddr_vm *remote, struct msghdr *msg,
>  			     size_t dgram_len)
> @@ -826,7 +821,6 @@ static struct vsock_transport hvs_transport = {
>  	.connect                  = hvs_connect,
>  	.shutdown                 = hvs_shutdown,
>  
> -	.dgram_bind               = hvs_dgram_bind,
>  	.dgram_enqueue            = hvs_dgram_enqueue,
>  	.dgram_allow              = hvs_dgram_allow,
>  
> diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
> index 66edffdbf303..ac2126c7dac5 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,
>  
> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> index 01ea1402ad40..ffcbdd77feaa 100644
> --- a/net/vmw_vsock/virtio_transport_common.c
> +++ b/net/vmw_vsock/virtio_transport_common.c
> @@ -781,13 +781,6 @@ 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);
> -
>  bool virtio_transport_dgram_allow(u32 cid, u32 port)
>  {
>  	return false;
> diff --git a/net/vmw_vsock/vmci_transport.c b/net/vmw_vsock/vmci_transport.c
> index 0bbbdb222245..857b0461f856 100644
> --- a/net/vmw_vsock/vmci_transport.c
> +++ b/net/vmw_vsock/vmci_transport.c
> @@ -2072,7 +2072,7 @@ static int __init vmci_transport_init(void)
>  	/* 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);
> +	err = vsock_core_register(&vmci_transport, VSOCK_TRANSPORT_F_DGRAM_FALLBACK);
>  	if (err < 0)
>  		goto err_unsubscribe;
>  
> diff --git a/net/vmw_vsock/vsock_loopback.c b/net/vmw_vsock/vsock_loopback.c
> index 2a59dd177c74..278235ea06c4 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,
>  
>