[PATCH net-next 1/2] vsock: support SO_INQ on stream sockets

[David Carlier <devnexen@gmail.com>]

SO_INQ makes recvmsg() return the bytes left in the receive queue in an
SCM_INQ cmsg, saving a SIOCINQ call per receive. AF_UNIX stream sockets
support it, AF_VSOCK fails with ENOPROTOOPT.

Add it for SOCK_STREAM, reusing the hint already computed for io_uring.
As with TCP_INQ, 1 is reported once the stream is finished so the caller
reads again and sees EOF. No cmsg is sent when the transport cannot
report the queue length.

SOCK_SEQPACKET is refused, as on AF_UNIX: its transport callback counts
messages, not bytes.

Signed-off-by: David Carlier <devnexen@gmail.com>
---
 include/net/af_vsock.h   |  1 +
 net/vmw_vsock/af_vsock.c | 41 +++++++++++++++++++++++++++++++---------
 2 files changed, 33 insertions(+), 9 deletions(-)

diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
index 5549298c1ec6..e8481f12312e 100644
--- a/include/net/af_vsock.h
+++ b/include/net/af_vsock.h
@@ -68,6 +68,7 @@ struct vsock_sock {
 	u64 buffer_size;
 	u64 buffer_min_size;
 	u64 buffer_max_size;
+	bool recvmsg_inq;
 
 	/* Private to transport. */
 	void *trans;
diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index 1c2d1cea67f4..874dc1545a35 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -2050,29 +2050,38 @@ static int vsock_connectible_setsockopt(struct socket *sock,
 	transport = vsk->transport;
 
 	if (level == SOL_SOCKET) {
-		int zerocopy;
+		int v;
 
-		if (optname != SO_ZEROCOPY) {
+		if (optname != SO_ZEROCOPY && optname != SO_INQ) {
 			release_sock(sk);
 			return sock_setsockopt(sock, level, optname, optval, optlen);
 		}
 
 		/* Use 'int' type here, because variable to
-		 * set this option usually has this type.
+		 * set these options usually has this type.
 		 */
-		COPY_IN(zerocopy);
+		COPY_IN(v);
 
-		if (zerocopy < 0 || zerocopy > 1) {
+		if (v < 0 || v > 1) {
 			err = -EINVAL;
 			goto exit;
 		}
 
+		if (optname == SO_INQ) {
+			if (sk->sk_type != SOCK_STREAM) {
+				err = -ENOPROTOOPT;
+				goto exit;
+			}
+			vsk->recvmsg_inq = v;
+			goto exit;
+		}
+
 		if (transport && !vsock_msgzerocopy_allow(transport)) {
 			err = -EOPNOTSUPP;
 			goto exit;
 		}
 
-		sock_valbool_flag(sk, SOCK_ZEROCOPY, zerocopy);
+		sock_valbool_flag(sk, SOCK_ZEROCOPY, v);
 		goto exit;
 	}
 
@@ -2581,6 +2590,7 @@ __vsock_connectible_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
 	struct sock *sk;
 	struct vsock_sock *vsk;
 	const struct vsock_transport *transport;
+	bool do_cmsg = false;
 	int err;
 
 	sk = sock->sk;
@@ -2637,13 +2647,26 @@ __vsock_connectible_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
 		err = __vsock_seqpacket_recvmsg(sk, msg, len, flags);
 
 out:
-	/* Seqpacket has_data counts messages, while io_uring treats msg_inq as
-	 * a byte length when sizing retries, so only streams report a hint.
+	/* Seqpacket has_data counts messages, while SCM_INQ reports bytes and
+	 * io_uring treats msg_inq as a byte length when sizing retries, so
+	 * only streams report it.
 	 */
-	if (msg->msg_get_inq && err >= 0 && sk->sk_type == SOCK_STREAM)
+	if ((vsk->recvmsg_inq | msg->msg_get_inq) && err >= 0 &&
+	    sk->sk_type == SOCK_STREAM) {
 		msg->msg_inq = vsock_stream_inq_hint(sk);
 
+		/* A negative hint means the transport could not tell. SCM_INQ
+		 * has no encoding for that, so report nothing.
+		 */
+		do_cmsg = vsk->recvmsg_inq && msg->msg_inq >= 0;
+	}
+
 	release_sock(sk);
+
+	if (do_cmsg)
+		put_cmsg(msg, SOL_SOCKET, SCM_INQ, sizeof(msg->msg_inq),
+			 &msg->msg_inq);
+
 	return err;
 }
 
-- 
2.55.0