[RFC PATCH v2 5/9] vsock: SO_RCVLOWAT transport set callback

[Arseniy Krasnov <AVKrasnov@sberdevices.ru>]

This adds transport specific callback for SO_RCVLOWAT, because in some
transports it may be difficult to know current available number of bytes
ready to read. Thus, when SO_RCVLOWAT is set, transport may reject it.

Signed-off-by: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
---
 include/net/af_vsock.h   |  1 +
 net/vmw_vsock/af_vsock.c | 19 +++++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
index f742e50207fb..eae5874bae35 100644
--- a/include/net/af_vsock.h
+++ b/include/net/af_vsock.h
@@ -134,6 +134,7 @@ struct vsock_transport {
 	u64 (*stream_rcvhiwat)(struct vsock_sock *);
 	bool (*stream_is_active)(struct vsock_sock *);
 	bool (*stream_allow)(u32 cid, u32 port);
+	int (*set_rcvlowat)(struct vsock_sock *, int);
 
 	/* SEQ_PACKET. */
 	ssize_t (*seqpacket_dequeue)(struct vsock_sock *vsk, struct msghdr *msg,
diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index 63a13fa2686a..b7a286db4af1 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -2130,6 +2130,24 @@ vsock_connectible_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
 	return err;
 }
 
+static int vsock_set_rcvlowat(struct sock *sk, int val)
+{
+	const struct vsock_transport *transport;
+	struct vsock_sock *vsk;
+	int err = 0;
+
+	vsk = vsock_sk(sk);
+	transport = vsk->transport;
+
+	if (transport->set_rcvlowat)
+		err = transport->set_rcvlowat(vsk, val);
+
+	if (!err)
+		WRITE_ONCE(sk->sk_rcvlowat, val ? : 1);
+
+	return err;
+}
+
 static const struct proto_ops vsock_stream_ops = {
 	.family = PF_VSOCK,
 	.owner = THIS_MODULE,
@@ -2149,6 +2167,7 @@ static const struct proto_ops vsock_stream_ops = {
 	.recvmsg = vsock_connectible_recvmsg,
 	.mmap = sock_no_mmap,
 	.sendpage = sock_no_sendpage,
+	.set_rcvlowat = vsock_set_rcvlowat,
 };
 
 static const struct proto_ops vsock_seqpacket_ops = {
-- 
2.25.1