Subject: Re: [PATCH RFC net-next v4 1/8] vsock/dgram: generalize recvmsg and drop transport->dgram_dequeue

From: Arseniy Krasnov <[email-masked]>
Date: Sun, 11 Jun 2023 23:43:15 +0300

Hello Bobby! Thanks for this patchset! Small comment below:

On 10.06.2023 03:58, Bobby Eshleman wrote:
> This commit drops the transport->dgram_dequeue callback and makes
> vsock_dgram_recvmsg() generic. It also adds additional transport
> callbacks for use by the generic vsock_dgram_recvmsg(), such as for
> parsing skbs for CID/port which vary in format per transport.
> 
> Signed-off-by: Bobby Eshleman <[email-masked]>
> ---
>  drivers/vhost/vsock.c                   |  4 +-
>  include/linux/virtio_vsock.h            |  3 ++
>  include/net/af_vsock.h                  | 13 ++++++-
>  net/vmw_vsock/af_vsock.c                | 51 ++++++++++++++++++++++++-
>  net/vmw_vsock/hyperv_transport.c        | 17 +++++++--
>  net/vmw_vsock/virtio_transport.c        |  4 +-
>  net/vmw_vsock/virtio_transport_common.c | 18 +++++++++
>  net/vmw_vsock/vmci_transport.c          | 68 +++++++++++++--------------------
>  net/vmw_vsock/vsock_loopback.c          |  4 +-
>  9 files changed, 132 insertions(+), 50 deletions(-)
> 
> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> index 6578db78f0ae..c8201c070b4b 100644
> --- a/drivers/vhost/vsock.c
> +++ b/drivers/vhost/vsock.c
> @@ -410,9 +410,11 @@ 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,
> +		.dgram_get_cid		  = virtio_transport_dgram_get_cid,
> +		.dgram_get_port		  = virtio_transport_dgram_get_port,
> +		.dgram_get_length	  = virtio_transport_dgram_get_length,
>  
>  		.stream_enqueue           = virtio_transport_stream_enqueue,
>  		.stream_dequeue           = virtio_transport_stream_dequeue,
> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
> index c58453699ee9..23521a318cf0 100644
> --- a/include/linux/virtio_vsock.h
> +++ b/include/linux/virtio_vsock.h
> @@ -219,6 +219,9 @@ 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);
> +int virtio_transport_dgram_get_length(struct sk_buff *skb, size_t *len);
>  
>  int virtio_transport_connect(struct vsock_sock *vsk);
>  
> diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
> index 0e7504a42925..7bedb9ee7e3e 100644
> --- a/include/net/af_vsock.h
> +++ b/include/net/af_vsock.h
> @@ -120,11 +120,20 @@ 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);
> +	int (*dgram_get_cid)(struct sk_buff *skb, unsigned int *cid);
> +	int (*dgram_get_port)(struct sk_buff *skb, unsigned int *port);
> +	int (*dgram_get_length)(struct sk_buff *skb, size_t *length);
> +
> +	/* The number of bytes into the buffer at which the payload starts, as
> +	 * first seen by the receiving socket layer. For example, if the
> +	 * transport presets the skb pointers using skb_pull(sizeof(header))
> +	 * than this would be zero, otherwise it would be the size of the
> +	 * header.
> +	 */
> +	const size_t dgram_payload_offset;
>  
>  	/* STREAM. */
>  	/* TODO: stream_bind() */
> diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> index efb8a0937a13..ffb4dd8b6ea7 100644
> --- a/net/vmw_vsock/af_vsock.c
> +++ b/net/vmw_vsock/af_vsock.c
> @@ -1271,11 +1271,15 @@ 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);
> @@ -1286,7 +1290,52 @@ 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;
> +
> +	err = transport->dgram_get_length(skb, &payload_len);
> +	if (err)
> +		goto out;
> +
> +	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, transport->dgram_payload_offset, 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);
> +		unsigned int cid, port;
> +
> +		err = transport->dgram_get_cid(skb, &cid);
> +		if (err)
> +			goto out;
> +
> +		err = transport->dgram_get_port(skb, &port);
> +		if (err)
> +			goto out;

Maybe we can merge 'dgram_get_cid' and 'dgram_get_port' to a single callback? Because I see that this is
the only place where both are used (correct me if i'm wrong) and logically both operates with addresses:
CID and port. E.g. something like that: dgram_get_cid_n_port().

Moreover, I'm not sure, but is it good "tradeoff" here: remove transport specific callback for dgram receive
where we already have 'msghdr' with both data buffer and buffer for 'sockaddr_vm' and instead of it add new
several fields (callbacks) to transports like dgram_get_cid(), dgram_get_port()? I agree, that in each transport
specific callback we will have same copying logic by calling 'skb_copy_datagram_msg()' and filling address
by using 'vsock_addr_init()', but in this case we don't need to update transports too much. For example HyperV
still unchanged as it does not support SOCK_DGRAM. For VMCI You just need to add 'vsock_addr_init()' logic
to it's dgram dequeue callback.

What do You think?

Thanks, Arseniy

> +
> +		vsock_addr_init(vm_addr, cid, port);
> +		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..ff6e87e25fa0 100644
> --- a/net/vmw_vsock/hyperv_transport.c
> +++ b/net/vmw_vsock/hyperv_transport.c
> @@ -556,8 +556,17 @@ 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)
> +static int hvs_dgram_get_cid(struct sk_buff *skb, unsigned int *cid)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
> +static int hvs_dgram_get_port(struct sk_buff *skb, unsigned int *port)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
> +static int hvs_dgram_get_length(struct sk_buff *skb, size_t *len)
>  {
>  	return -EOPNOTSUPP;
>  }
> @@ -833,7 +842,9 @@ static struct vsock_transport hvs_transport = {
>  	.shutdown                 = hvs_shutdown,
>  
>  	.dgram_bind               = hvs_dgram_bind,
> -	.dgram_dequeue            = hvs_dgram_dequeue,
> +	.dgram_get_cid		  = hvs_dgram_get_cid,
> +	.dgram_get_port		  = hvs_dgram_get_port,
> +	.dgram_get_length	  = hvs_dgram_get_length,
>  	.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..5763cdf13804 100644
> --- a/net/vmw_vsock/virtio_transport.c
> +++ b/net/vmw_vsock/virtio_transport.c
> @@ -429,9 +429,11 @@ 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,
> +		.dgram_get_cid		  = virtio_transport_dgram_get_cid,
> +		.dgram_get_port		  = virtio_transport_dgram_get_port,
> +		.dgram_get_length	  = virtio_transport_dgram_get_length,
>  
>  		.stream_dequeue           = virtio_transport_stream_dequeue,
>  		.stream_enqueue           = virtio_transport_stream_enqueue,
> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> index b769fc258931..e6903c719964 100644
> --- a/net/vmw_vsock/virtio_transport_common.c
> +++ b/net/vmw_vsock/virtio_transport_common.c
> @@ -797,6 +797,24 @@ int virtio_transport_dgram_bind(struct vsock_sock *vsk,
>  }
>  EXPORT_SYMBOL_GPL(virtio_transport_dgram_bind);
>  
> +int virtio_transport_dgram_get_cid(struct sk_buff *skb, unsigned int *cid)
> +{
> +	return -EOPNOTSUPP;
> +}
> +EXPORT_SYMBOL_GPL(virtio_transport_dgram_get_cid);
> +
> +int virtio_transport_dgram_get_port(struct sk_buff *skb, unsigned int *port)
> +{
> +	return -EOPNOTSUPP;
> +}
> +EXPORT_SYMBOL_GPL(virtio_transport_dgram_get_port);
> +
> +int virtio_transport_dgram_get_length(struct sk_buff *skb, size_t *len)
> +{
> +	return -EOPNOTSUPP;
> +}
> +EXPORT_SYMBOL_GPL(virtio_transport_dgram_get_length);
> +
>  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 b370070194fa..bbc63826bf48 100644
> --- a/net/vmw_vsock/vmci_transport.c
> +++ b/net/vmw_vsock/vmci_transport.c
> @@ -1731,57 +1731,40 @@ 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 int vmci_transport_dgram_get_cid(struct sk_buff *skb, unsigned int *cid)
>  {
> -	int err;
>  	struct vmci_datagram *dg;
> -	size_t payload_len;
> -	struct sk_buff *skb;
>  
> -	if (flags & MSG_OOB || flags & MSG_ERRQUEUE)
> -		return -EOPNOTSUPP;
> +	dg = (struct vmci_datagram *)skb->data;
> +	if (!dg)
> +		return -EINVAL;
>  
> -	/* 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;
> +	*cid = dg->src.context;
> +	return 0;
> +}
> +
> +static int vmci_transport_dgram_get_port(struct sk_buff *skb, unsigned int *port)
> +{
> +	struct vmci_datagram *dg;
>  
>  	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;
> -	}
> +		return -EINVAL;
>  
> -	if (payload_len > len) {
> -		payload_len = len;
> -		msg->msg_flags |= MSG_TRUNC;
> -	}
> +	*port = dg->src.resource;
> +	return 0;
> +}
>  
> -	/* Place the datagram payload in the user's iovec. */
> -	err = skb_copy_datagram_msg(skb, sizeof(*dg), msg, payload_len);
> -	if (err)
> -		goto out;
> +static int vmci_transport_dgram_get_length(struct sk_buff *skb, size_t *len)
> +{
> +	struct vmci_datagram *dg;
>  
> -	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;
> +	dg = (struct vmci_datagram *)skb->data;
> +	if (!dg)
> +		return -EINVAL;
>  
> -out:
> -	skb_free_datagram(&vsk->sk, skb);
> -	return err;
> +	*len = dg->payload_size;
> +	return 0;
>  }
>  
>  static bool vmci_transport_dgram_allow(u32 cid, u32 port)
> @@ -2040,9 +2023,12 @@ 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_get_cid = vmci_transport_dgram_get_cid,
> +	.dgram_get_port = vmci_transport_dgram_get_port,
> +	.dgram_get_length = vmci_transport_dgram_get_length,
> +	.dgram_payload_offset = sizeof(struct vmci_datagram),
>  	.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..2f3cabc79ee5 100644
> --- a/net/vmw_vsock/vsock_loopback.c
> +++ b/net/vmw_vsock/vsock_loopback.c
> @@ -62,9 +62,11 @@ 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,
> +		.dgram_get_cid		  = virtio_transport_dgram_get_cid,
> +		.dgram_get_port		  = virtio_transport_dgram_get_port,
> +		.dgram_get_length	  = virtio_transport_dgram_get_length,
>  
>  		.stream_dequeue           = virtio_transport_stream_dequeue,
>  		.stream_enqueue           = virtio_transport_stream_enqueue,
>