Re: [PATCH RFC net-next v3 1/8] vsock/dgram: generalize recvmsg and drop transport->dgram_dequeue

[Bobby Eshleman]

On Wed, May 31, 2023 at 05:56:48PM +0200, Simon Horman wrote:
> On Wed, May 31, 2023 at 12:35:05AM +0000, 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@xxxxxxxxxxxxx>
> 
> ...
> 
> > diff --git a/net/vmw_vsock/vmci_transport.c b/net/vmw_vsock/vmci_transport.c
> > index b370070194fa..b6a51afb74b8 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)
> > +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;
> > +}
> 
> Hi Bobby,
> 
> clang-16 with W=1 seems a bit unhappy about this.
> 
>   net/vmw_vsock/vmci_transport.c:1734:5: warning: no previous prototype for function 'vmci_transport_dgram_get_cid' [-Wmissing-prototypes]
>   int vmci_transport_dgram_get_cid(struct sk_buff *skb, unsigned int *cid)
>       ^
>   net/vmw_vsock/vmci_transport.c:1734:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
>   int vmci_transport_dgram_get_cid(struct sk_buff *skb, unsigned int *cid)
>   ^
>   static 
>   net/vmw_vsock/vmci_transport.c:1746:5: warning: no previous prototype for function 'vmci_transport_dgram_get_port' [-Wmissing-prototypes]
>   int vmci_transport_dgram_get_port(struct sk_buff *skb, unsigned int *port)
>       ^
>   net/vmw_vsock/vmci_transport.c:1746:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
>   int vmci_transport_dgram_get_port(struct sk_buff *skb, unsigned int *port)
>   ^
>   static 
>   net/vmw_vsock/vmci_transport.c:1758:5: warning: no previous prototype for function 'vmci_transport_dgram_get_length' [-Wmissing-prototypes]
>   int vmci_transport_dgram_get_length(struct sk_buff *skb, size_t *len)
>       ^
>   net/vmw_vsock/vmci_transport.c:1758:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
>   int vmci_transport_dgram_get_length(struct sk_buff *skb, size_t *len)
>   ^
> 
> I see similar warnings for net/vmw_vsock/af_vsock.c in patch 4/8.
> 
> > +
> > +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;
> > +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)
> 
> ...

Thanks for the review! Your feedback from both emails will be
incorporated in the next rev (with C=1 and W=1 output clearing).

Thanks again,
Bobby