Re: [RFC PATCH v6 04/22] af_vsock: implement SEQPACKET receive loop

[Stefano Garzarella]

On Sun, Mar 07, 2021 at 08:59:45PM +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>
> ---
> include/net/af_vsock.h   |  5 +++
> net/vmw_vsock/af_vsock.c | 95 +++++++++++++++++++++++++++++++++++++++-
> 2 files changed, 99 insertions(+), 1 deletion(-)
>
> diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
> index b1c717286993..5ad7ee7f78fd 100644
> --- a/include/net/af_vsock.h
> +++ b/include/net/af_vsock.h
> @@ -135,6 +135,11 @@ struct vsock_transport {
> 	bool (*stream_is_active)(struct vsock_sock *);
> 	bool (*stream_allow)(u32 cid, u32 port);
>
> +	/* SEQ_PACKET. */
> +	size_t (*seqpacket_seq_get_len)(struct vsock_sock *vsk);
> +	int (*seqpacket_dequeue)(struct vsock_sock *vsk, struct msghdr *msg,
> +				 int flags, bool *msg_ready);
> +
> 	/* 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..ac2f69362f2e 100644
> --- a/net/vmw_vsock/af_vsock.c
> +++ b/net/vmw_vsock/af_vsock.c
> @@ -1973,6 +1973,96 @@ 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;
> +		}
> +
> +		if (record_len == 0) {
> +			record_len =
> +				transport->seqpacket_seq_get_len(vsk);
> +
> +			if (record_len == 0)
> +				continue;
> +		}
> +
> +		err = transport->seqpacket_dequeue(vsk, msg, flags, &msg_ready);

In order to simplify the transport interface, can we do the work of 
seqpacket_seq_get_len() at the beginning of seqpacket_dequeue()?

So in this way seqpacket_dequeue() can return the 'record_len' or an 
error.