Re: [PATCH RFC net-next v5 01/14] af_vsock: generalize vsock_dgram_recvmsg() to all transports

[Arseniy Krasnov]

On 19.07.2023 03:50, Bobby Eshleman wrote:
> This commit drops the transport->dgram_dequeue callback and makes
> vsock_dgram_recvmsg() generic to all transports.
> 
> To make this possible, two transport-level changes are introduced:
> - implementation of the ->dgram_addr_init() callback to initialize
>   the sockaddr_vm structure with data from incoming socket buffers.
> - transport implementations set the skb->data pointer to the beginning
>   of the payload prior to adding the skb to the socket's receive queue.
>   That is, they must use skb_pull() before enqueuing. This is an
>   agreement between the transport and the socket layer that skb->data
>   always points to the beginning of the payload (and not, for example,
>   the packet header).
> 
> Signed-off-by: Bobby Eshleman <bobby.eshleman@xxxxxxxxxxxxx>
> ---
>  drivers/vhost/vsock.c                   |  1 -
>  include/linux/virtio_vsock.h            |  5 ---
>  include/net/af_vsock.h                  |  3 +-
>  net/vmw_vsock/af_vsock.c                | 40 ++++++++++++++++++++++-
>  net/vmw_vsock/hyperv_transport.c        |  7 ----
>  net/vmw_vsock/virtio_transport.c        |  1 -
>  net/vmw_vsock/virtio_transport_common.c |  9 -----
>  net/vmw_vsock/vmci_transport.c          | 58 ++++++---------------------------
>  net/vmw_vsock/vsock_loopback.c          |  1 -
>  9 files changed, 50 insertions(+), 75 deletions(-)
> 
> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> index 6578db78f0ae..ae8891598a48 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_dequeue            = virtio_transport_dgram_dequeue,
>  		.dgram_bind               = virtio_transport_dgram_bind,
>  		.dgram_allow              = virtio_transport_dgram_allow,
>  
> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
> index c58453699ee9..18cbe8d37fca 100644
> --- a/include/linux/virtio_vsock.h
> +++ b/include/linux/virtio_vsock.h
> @@ -167,11 +167,6 @@ virtio_transport_stream_dequeue(struct vsock_sock *vsk,
>  				size_t len,
>  				int type);
>  int
> -virtio_transport_dgram_dequeue(struct vsock_sock *vsk,
> -			       struct msghdr *msg,
> -			       size_t len, int flags);
> -
> -int
>  virtio_transport_seqpacket_enqueue(struct vsock_sock *vsk,
>  				   struct msghdr *msg,
>  				   size_t len);
> diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
> index 0e7504a42925..305d57502e89 100644
> --- a/include/net/af_vsock.h
> +++ b/include/net/af_vsock.h
> @@ -120,11 +120,10 @@ struct vsock_transport {
>  
>  	/* DGRAM. */
>  	int (*dgram_bind)(struct vsock_sock *, struct sockaddr_vm *);
> -	int (*dgram_dequeue)(struct vsock_sock *vsk, struct msghdr *msg,
> -			     size_t len, int flags);
>  	int (*dgram_enqueue)(struct vsock_sock *, struct sockaddr_vm *,
>  			     struct msghdr *, size_t len);
>  	bool (*dgram_allow)(u32 cid, u32 port);
> +	void (*dgram_addr_init)(struct sk_buff *skb, struct sockaddr_vm *addr);
>  
>  	/* STREAM. */
>  	/* TODO: stream_bind() */
> diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> index deb72a8c44a7..ad71e084bf2f 100644
> --- a/net/vmw_vsock/af_vsock.c
> +++ b/net/vmw_vsock/af_vsock.c
> @@ -1272,11 +1272,15 @@ static int vsock_dgram_connect(struct socket *sock,
>  int vsock_dgram_recvmsg(struct socket *sock, struct msghdr *msg,
>  			size_t len, int flags)
>  {
> +	const struct vsock_transport *transport;
>  #ifdef CONFIG_BPF_SYSCALL
>  	const struct proto *prot;
>  #endif
>  	struct vsock_sock *vsk;
> +	struct sk_buff *skb;
> +	size_t payload_len;
>  	struct sock *sk;
> +	int err;
>  
>  	sk = sock->sk;
>  	vsk = vsock_sk(sk);
> @@ -1287,7 +1291,41 @@ int vsock_dgram_recvmsg(struct socket *sock, struct msghdr *msg,
>  		return prot->recvmsg(sk, msg, len, flags, NULL);
>  #endif
>  
> -	return vsk->transport->dgram_dequeue(vsk, msg, len, flags);
> +	if (flags & MSG_OOB || flags & MSG_ERRQUEUE)
> +		return -EOPNOTSUPP;
> +
> +	transport = vsk->transport;
> +
> +	/* Retrieve the head sk_buff from the socket's receive queue. */
> +	err = 0;
> +	skb = skb_recv_datagram(sk_vsock(vsk), flags, &err);
> +	if (!skb)
> +		return err;
> +
> +	payload_len = skb->len;
> +
> +	if (payload_len > len) {
> +		payload_len = len;
> +		msg->msg_flags |= MSG_TRUNC;
> +	}
> +
> +	/* Place the datagram payload in the user's iovec. */
> +	err = skb_copy_datagram_msg(skb, 0, msg, payload_len);
> +	if (err)
> +		goto out;
> +
> +	if (msg->msg_name) {
> +		/* Provide the address of the sender. */
> +		DECLARE_SOCKADDR(struct sockaddr_vm *, vm_addr, msg->msg_name);
> +
> +		transport->dgram_addr_init(skb, vm_addr);

Do we need check that dgram_addr_init != NULL? because I see that not all transports have this
callback set in this patch

> +		msg->msg_namelen = sizeof(*vm_addr);
> +	}
> +	err = payload_len;
> +
> +out:
> +	skb_free_datagram(&vsk->sk, skb);
> +	return err;
>  }
>  EXPORT_SYMBOL_GPL(vsock_dgram_recvmsg);
>  
> diff --git a/net/vmw_vsock/hyperv_transport.c b/net/vmw_vsock/hyperv_transport.c
> index 7cb1a9d2cdb4..7f1ea434656d 100644
> --- a/net/vmw_vsock/hyperv_transport.c
> +++ b/net/vmw_vsock/hyperv_transport.c
> @@ -556,12 +556,6 @@ static int hvs_dgram_bind(struct vsock_sock *vsk, struct sockaddr_vm *addr)
>  	return -EOPNOTSUPP;
>  }
>  
> -static int hvs_dgram_dequeue(struct vsock_sock *vsk, struct msghdr *msg,
> -			     size_t len, int flags)
> -{
> -	return -EOPNOTSUPP;
> -}
> -
>  static int hvs_dgram_enqueue(struct vsock_sock *vsk,
>  			     struct sockaddr_vm *remote, struct msghdr *msg,
>  			     size_t dgram_len)
> @@ -833,7 +827,6 @@ static struct vsock_transport hvs_transport = {
>  	.shutdown                 = hvs_shutdown,
>  
>  	.dgram_bind               = hvs_dgram_bind,
> -	.dgram_dequeue            = hvs_dgram_dequeue,
>  	.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 e95df847176b..66edffdbf303 100644
> --- a/net/vmw_vsock/virtio_transport.c
> +++ b/net/vmw_vsock/virtio_transport.c
> @@ -429,7 +429,6 @@ static struct virtio_transport virtio_transport = {
>  		.cancel_pkt               = virtio_transport_cancel_pkt,
>  
>  		.dgram_bind               = virtio_transport_dgram_bind,
> -		.dgram_dequeue            = virtio_transport_dgram_dequeue,
>  		.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 b769fc258931..01ea1402ad40 100644
> --- a/net/vmw_vsock/virtio_transport_common.c
> +++ b/net/vmw_vsock/virtio_transport_common.c
> @@ -583,15 +583,6 @@ virtio_transport_seqpacket_enqueue(struct vsock_sock *vsk,
>  }
>  EXPORT_SYMBOL_GPL(virtio_transport_seqpacket_enqueue);
>  
> -int
> -virtio_transport_dgram_dequeue(struct vsock_sock *vsk,
> -			       struct msghdr *msg,
> -			       size_t len, int flags)
> -{
> -	return -EOPNOTSUPP;
> -}
> -EXPORT_SYMBOL_GPL(virtio_transport_dgram_dequeue);
> -
>  s64 virtio_transport_stream_has_data(struct vsock_sock *vsk)
>  {
>  	struct virtio_vsock_sock *vvs = vsk->trans;
> diff --git a/net/vmw_vsock/vmci_transport.c b/net/vmw_vsock/vmci_transport.c
> index b370070194fa..0bbbdb222245 100644
> --- a/net/vmw_vsock/vmci_transport.c
> +++ b/net/vmw_vsock/vmci_transport.c
> @@ -641,6 +641,7 @@ static int vmci_transport_recv_dgram_cb(void *data, struct vmci_datagram *dg)
>  	sock_hold(sk);
>  	skb_put(skb, size);
>  	memcpy(skb->data, dg, size);
> +	skb_pull(skb, VMCI_DG_HEADERSIZE);
>  	sk_receive_skb(sk, skb, 0);
>  
>  	return VMCI_SUCCESS;
> @@ -1731,57 +1732,18 @@ static int vmci_transport_dgram_enqueue(
>  	return err - sizeof(*dg);
>  }
>  
> -static int vmci_transport_dgram_dequeue(struct vsock_sock *vsk,
> -					struct msghdr *msg, size_t len,
> -					int flags)
> +static void vmci_transport_dgram_addr_init(struct sk_buff *skb,
> +					   struct sockaddr_vm *addr)
>  {
> -	int err;
>  	struct vmci_datagram *dg;
> -	size_t payload_len;
> -	struct sk_buff *skb;
> -
> -	if (flags & MSG_OOB || flags & MSG_ERRQUEUE)
> -		return -EOPNOTSUPP;
> -
> -	/* Retrieve the head sk_buff from the socket's receive queue. */
> -	err = 0;
> -	skb = skb_recv_datagram(&vsk->sk, flags, &err);
> -	if (!skb)
> -		return err;
> -
> -	dg = (struct vmci_datagram *)skb->data;
> -	if (!dg)
> -		/* err is 0, meaning we read zero bytes. */
> -		goto out;
> -
> -	payload_len = dg->payload_size;
> -	/* Ensure the sk_buff matches the payload size claimed in the packet. */
> -	if (payload_len != skb->len - sizeof(*dg)) {
> -		err = -EINVAL;
> -		goto out;
> -	}
> -
> -	if (payload_len > len) {
> -		payload_len = len;
> -		msg->msg_flags |= MSG_TRUNC;
> -	}
> +	unsigned int cid, port;
>  
> -	/* Place the datagram payload in the user's iovec. */
> -	err = skb_copy_datagram_msg(skb, sizeof(*dg), msg, payload_len);
> -	if (err)
> -		goto out;
> -
> -	if (msg->msg_name) {
> -		/* Provide the address of the sender. */
> -		DECLARE_SOCKADDR(struct sockaddr_vm *, vm_addr, msg->msg_name);
> -		vsock_addr_init(vm_addr, dg->src.context, dg->src.resource);
> -		msg->msg_namelen = sizeof(*vm_addr);
> -	}
> -	err = payload_len;
> +	WARN_ONCE(skb->head == skb->data, "vmci vsock bug: bad dgram skb");
>  
> -out:
> -	skb_free_datagram(&vsk->sk, skb);
> -	return err;
> +	dg = (struct vmci_datagram *)skb->head;
> +	cid = dg->src.context;
> +	port = dg->src.resource;
> +	vsock_addr_init(addr, cid, port);

I think we

1) can short this to:

vsock_addr_init(addr, dg->src.context, dg->src.resource);

2) w/o previous point, cid and port better be u32, as VMCI structure has u32 fields 'context' and
   'resource' and 'vsock_addr_init()' also has u32 type for both arguments.

Thanks, Arseniy

>  }
>  
>  static bool vmci_transport_dgram_allow(u32 cid, u32 port)
> @@ -2040,9 +2002,9 @@ static struct vsock_transport vmci_transport = {
>  	.release = vmci_transport_release,
>  	.connect = vmci_transport_connect,
>  	.dgram_bind = vmci_transport_dgram_bind,
> -	.dgram_dequeue = vmci_transport_dgram_dequeue,
>  	.dgram_enqueue = vmci_transport_dgram_enqueue,
>  	.dgram_allow = vmci_transport_dgram_allow,
> +	.dgram_addr_init = vmci_transport_dgram_addr_init,
>  	.stream_dequeue = vmci_transport_stream_dequeue,
>  	.stream_enqueue = vmci_transport_stream_enqueue,
>  	.stream_has_data = vmci_transport_stream_has_data,
> diff --git a/net/vmw_vsock/vsock_loopback.c b/net/vmw_vsock/vsock_loopback.c
> index 5c6360df1f31..2a59dd177c74 100644
> --- a/net/vmw_vsock/vsock_loopback.c
> +++ b/net/vmw_vsock/vsock_loopback.c
> @@ -62,7 +62,6 @@ static struct virtio_transport loopback_transport = {
>  		.cancel_pkt               = vsock_loopback_cancel_pkt,
>  
>  		.dgram_bind               = virtio_transport_dgram_bind,
> -		.dgram_dequeue            = virtio_transport_dgram_dequeue,
>  		.dgram_enqueue            = virtio_transport_dgram_enqueue,
>  		.dgram_allow              = virtio_transport_dgram_allow,
>  
>