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

  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 <bobby.eshleman@bytedance.com>
---
 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(-)
  

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 <bobby.eshleman@bytedance.com>
> ---
>  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,
>
  

On Sun, Jun 11, 2023 at 11:43:15PM +0300, Arseniy Krasnov wrote:
>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 <bobby.eshleman@bytedance.com>
>> ---
>>  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);

What about ssize_t return value here?

Or maybe a single callback that return both length and offset?

.dgram_get_payload_info(skb, &payload_len, &payload_off)

>> +	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().

What about .dgram_addr_init(struct sk_buff *skb, struct sockaddr_vm *addr)
and the transport can set cid and 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?

Honestly, I'd rather avoid duplicate code than reduce changes in
transports that don't support dgram.

One thing I do agree on though is minimizing the number of callbacks
to call to reduce the number of indirection (more performance?).

Thanks,
Stefano

>
>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,
>>
>
  

On 22.06.2023 17:51, Stefano Garzarella wrote:
> On Sun, Jun 11, 2023 at 11:43:15PM +0300, Arseniy Krasnov wrote:
>> 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 <bobby.eshleman@bytedance.com>
>>> ---
>>>  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);
> 
> What about ssize_t return value here?
> 
> Or maybe a single callback that return both length and offset?
> 
> .dgram_get_payload_info(skb, &payload_len, &payload_off)

Just architectural question:

May be we can avoid this callback for length? IIUC concept of skbuff is that
current level of network stack already have pointer to its data 'skb->data' and
length of the payload 'skb->len' (both are set by previous stack handler - transport in
this case), so here we can use just 'skb->len' and thats all. There is no need to ask
lower level of network stack for length of payload? I see that VMCI stores metadata
with payload in 'data' buffer, but may be it is more correctly to do 'skb_pull()'
in vmci before inserting skbuff to sockets queue? In this case field with dgram payload
offset could be removed from transport.

Thanks, Arseniy

> 
>>> +    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().
> 
> What about .dgram_addr_init(struct sk_buff *skb, struct sockaddr_vm *addr)
> and the transport can set cid and 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?
> 
> Honestly, I'd rather avoid duplicate code than reduce changes in
> transports that don't support dgram.
> 
> One thing I do agree on though is minimizing the number of callbacks
> to call to reduce the number of indirection (more performance?).
> 
> Thanks,
> Stefano
> 
>>
>> 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,
>>>
>>
>
  

On Sun, Jun 11, 2023 at 11:43:15PM +0300, Arseniy Krasnov wrote:
> 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 <bobby.eshleman@bytedance.com>
> > ---
> >  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().

I like this idea.

> 
> 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
> 

I tend to agree with your point here that adding this many callbacks is
not the big win in complexity reduction that we're hoping for.

I also agree with Stefano's assessment that having two near identical
implementations is not good either.

Hopefully having one simpler callback will bring the best of both
worlds?

Best,
Bobby

> > +
> > +		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,
> >
  

On Thu, Jun 22, 2023 at 10:23:26PM +0300, Arseniy Krasnov wrote:
> 
> 
> On 22.06.2023 17:51, Stefano Garzarella wrote:
> > On Sun, Jun 11, 2023 at 11:43:15PM +0300, Arseniy Krasnov wrote:
> >> 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 <bobby.eshleman@bytedance.com>
> >>> ---
> >>>  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);
> > 
> > What about ssize_t return value here?
> > 
> > Or maybe a single callback that return both length and offset?
> > 
> > .dgram_get_payload_info(skb, &payload_len, &payload_off)
> 
> Just architectural question:
> 
> May be we can avoid this callback for length? IIUC concept of skbuff is that
> current level of network stack already have pointer to its data 'skb->data' and
> length of the payload 'skb->len' (both are set by previous stack handler - transport in
> this case), so here we can use just 'skb->len' and thats all. There is no need to ask
> lower level of network stack for length of payload? I see that VMCI stores metadata
> with payload in 'data' buffer, but may be it is more correctly to do 'skb_pull()'
> in vmci before inserting skbuff to sockets queue? In this case field with dgram payload
> offset could be removed from transport.
> 
> Thanks, Arseniy
> 

I agree, I think introducing the skb_pull() to vmci would honestly be
best. I don't think it should break anything based on my reading of the
code if it is called just prior to sk_receive_skb().


Thanks,
Bobby

> > 
> >>> +    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().
> > 
> > What about .dgram_addr_init(struct sk_buff *skb, struct sockaddr_vm *addr)
> > and the transport can set cid and 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?
> > 
> > Honestly, I'd rather avoid duplicate code than reduce changes in
> > transports that don't support dgram.
> > 
> > One thing I do agree on though is minimizing the number of callbacks
> > to call to reduce the number of indirection (more performance?).
> > 
> > Thanks,
> > Stefano
> > 
> >>
> >> 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,
> >>>
> >>
> >
  

On Thu, Jun 22, 2023 at 04:51:41PM +0200, Stefano Garzarella wrote:
> On Sun, Jun 11, 2023 at 11:43:15PM +0300, Arseniy Krasnov wrote:
> > 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 <bobby.eshleman@bytedance.com>
> > > ---
> > >  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);
> 
> What about ssize_t return value here?
> 
> Or maybe a single callback that return both length and offset?
> 
> .dgram_get_payload_info(skb, &payload_len, &payload_off)
> 

What are your thoughts on Arseniy's idea of using skb->len and adding a
skb_pull() just before vmci adds the skb to the sk receive queue?

> > > +	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().
> 
> What about .dgram_addr_init(struct sk_buff *skb, struct sockaddr_vm *addr)
> and the transport can set cid and port?
> 

LGTM!

> > 
> > 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?
> 
> Honestly, I'd rather avoid duplicate code than reduce changes in
> transports that don't support dgram.
> 
> One thing I do agree on though is minimizing the number of callbacks
> to call to reduce the number of indirection (more performance?).
> 
> Thanks,
> Stefano
> 

Thanks!

Best,
Bobby

> > 
> > 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,
> > > 
> > 
> 
> _______________________________________________
> Virtualization mailing list
> Virtualization@lists.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/virtualization
  

On Thu, Jun 22, 2023 at 11:37:42PM +0000, Bobby Eshleman wrote:
>On Thu, Jun 22, 2023 at 04:51:41PM +0200, Stefano Garzarella wrote:
>> On Sun, Jun 11, 2023 at 11:43:15PM +0300, Arseniy Krasnov wrote:
>> > 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 <bobby.eshleman@bytedance.com>
>> > > ---
>> > >  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);
>>
>> What about ssize_t return value here?
>>
>> Or maybe a single callback that return both length and offset?
>>
>> .dgram_get_payload_info(skb, &payload_len, &payload_off)
>>
>
>What are your thoughts on Arseniy's idea of using skb->len and adding a
>skb_pull() just before vmci adds the skb to the sk receive queue?

Yep, I agree on that!

Thanks,
Stefano