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

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Date:   Fri, 12 Mar 2021 16:17:47 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Arseny Krasnov <arseny.krasnov@...persky.com>
Cc:     Stefan Hajnoczi <stefanha@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jorgen Hansen <jhansen@...are.com>,
        Colin Ian King <colin.king@...onical.com>,
        Norbert Slusarek <nslusarek@....net>,
        Andra Paraschiv <andraprs@...zon.com>, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, stsp2@...dex.ru, oxffffaa@...il.com
Subject: Re: [RFC PATCH v6 04/22] af_vsock: implement SEQPACKET receive loop

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@...persky.com>
>---
> 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.