Re: [RFC PATCH v7 04/22] af_vsock: implement SEQPACKET receive loop

[Stefano Garzarella]

On Tue, Mar 23, 2021 at 04:10:03PM +0300, Arseny Krasnov wrote:
> This adds receive loop for SEQPACKET. It looks like receive loop for
> STREAM, but there is a little bit difference:
> 1) It doesn't call notify callbacks.
> 2) It doesn't care about 'SO_SNDLOWAT' and 'SO_RCVLOWAT' values, because
>   there is no sense for these values in SEQPACKET case.
> 3) It waits until whole record is received or error is found during
>   receiving.
> 4) It processes and sets 'MSG_TRUNC' flag.
>
> So to avoid extra conditions for two types of socket inside one loop, two
> independent functions were created.
>
> Signed-off-by: Arseny Krasnov <arseny.krasnov@xxxxxxxxxxxxx>
> ---
> v6 -> v7:
> 'seqpacket_get_len' callback now removed, length of message is returned
>  by 'seqpacket_dequeue' callback.
>
> include/net/af_vsock.h   |  4 ++
> net/vmw_vsock/af_vsock.c | 88 +++++++++++++++++++++++++++++++++++++++-
> 2 files changed, 91 insertions(+), 1 deletion(-)
>
> diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
> index b1c717286993..74ac8a4c4168 100644
> --- a/include/net/af_vsock.h
> +++ b/include/net/af_vsock.h
> @@ -135,6 +135,10 @@ struct vsock_transport {
> 	bool (*stream_is_active)(struct vsock_sock *);
> 	bool (*stream_allow)(u32 cid, u32 port);
>
> +	/* SEQ_PACKET. */
> +	int (*seqpacket_dequeue)(struct vsock_sock *vsk, struct msghdr *msg,
> +				 int flags, bool *msg_ready, size_t *record_len);
> +

Why not using ssize_t as return value and return the length or a 
negative value in case of error?

In this way we can remove the 'record_len' parameter.

> 	/* Notification. */
> 	int (*notify_poll_in)(struct vsock_sock *, size_t, bool *);
> 	int (*notify_poll_out)(struct vsock_sock *, size_t, bool *);
> diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> index 0bc661e54262..fa0c37f97330 100644
> --- a/net/vmw_vsock/af_vsock.c
> +++ b/net/vmw_vsock/af_vsock.c
> @@ -1973,6 +1973,89 @@ static int __vsock_stream_recvmsg(struct sock 
> *sk, struct msghdr *msg,
> 	return err;
> }
>
> +static int __vsock_seqpacket_recvmsg(struct sock *sk, struct msghdr 
> *msg,
> +				     size_t len, int flags)
> +{
> +	const struct vsock_transport *transport;
> +	const struct iovec *orig_iov;
> +	unsigned long orig_nr_segs;
> +	bool msg_ready;
> +	struct vsock_sock *vsk;
> +	size_t record_len;
> +	long timeout;
> +	int err = 0;
> +	DEFINE_WAIT(wait);
> +
> +	vsk = vsock_sk(sk);
> +	transport = vsk->transport;
> +
> +	timeout = sock_rcvtimeo(sk, flags & MSG_DONTWAIT);
> +	orig_nr_segs = msg->msg_iter.nr_segs;
> +	orig_iov = msg->msg_iter.iov;
> +	msg_ready = false;
> +	record_len = 0;
> +
> +	while (1) {
> +		err = vsock_wait_data(sk, &wait, timeout, NULL, 0);
> +
> +		if (err <= 0) {
> +			/* In case of any loop break(timeout, signal
> +			 * interrupt or shutdown), we report user that
> +			 * nothing was copied.
> +			 */
> +			err = 0;
> +			break;
> +		}
> +
> +		err = transport->seqpacket_dequeue(vsk, msg, flags, &msg_ready, &record_len);
> +
> +		if (err < 0) {
> +			if (err == -EAGAIN) {
> +				iov_iter_init(&msg->msg_iter, READ,
> +					      orig_iov, orig_nr_segs,
> +					      len);
> +				/* Clear 'MSG_EOR' here, because dequeue
> +				 * callback above set it again if it was
> +				 * set by sender. This 'MSG_EOR' is from
> +				 * dropped record.
> +				 */
> +				msg->msg_flags &= ~MSG_EOR;
> +				record_len = 0;
> +				continue;
> +			}
> +
> +			err = -ENOMEM;
> +			break;
> +		}
> +
> +		if (msg_ready)
> +			break;
> +	}
> +
> +	if (sk->sk_err)
> +		err = -sk->sk_err;
> +	else if (sk->sk_shutdown & RCV_SHUTDOWN)
> +		err = 0;
> +
> +	if (msg_ready) {

If 'err' is not 0, should we skip this branch?

> +		/* User sets MSG_TRUNC, so return real length of
> +		 * packet.
> +		 */
> +		if (flags & MSG_TRUNC)
> +			err = record_len;
> +		else
> +			err = len - msg->msg_iter.count;
> +
> +		/* Always set MSG_TRUNC if real length of packet is
> +		 * bigger than user's buffer.
> +		 */
> +		if (record_len > len)
> +			msg->msg_flags |= MSG_TRUNC;
> +	}
> +
> +	return err;
> +}
> +
> static int
> vsock_connectible_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
> 			  int flags)
> @@ -2028,7 +2111,10 @@ vsock_connectible_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
> 		goto out;
> 	}
>
> -	err = __vsock_stream_recvmsg(sk, msg, len, flags);
> +	if (sk->sk_type == SOCK_STREAM)
> +		err = __vsock_stream_recvmsg(sk, msg, len, flags);
> +	else
> +		err = __vsock_seqpacket_recvmsg(sk, msg, len, flags);
>
> out:
> 	release_sock(sk);
> --
> 2.25.1