Re: [PATCH net-next v2 1/2] vsock: support SO_INQ on stream sockets

[Stefano Garzarella <sgarzare@redhat.com>]

On Thu, Oct 15, 2026 at 04:43:33PM +0100, David Carlier wrote:
>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, and accepted sockets inherit the setting from
>the listener. 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 | 111 +++++++++++++++++++++++++++++----------
> 2 files changed, 84 insertions(+), 28 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..186ed57fd797 100644
>--- a/net/vmw_vsock/af_vsock.c
>+++ b/net/vmw_vsock/af_vsock.c
>@@ -984,6 +984,7 @@ static struct sock *__vsock_create(struct net *net,
> 		vsk->buffer_size = psk->buffer_size;
> 		vsk->buffer_min_size = psk->buffer_min_size;
> 		vsk->buffer_max_size = psk->buffer_max_size;
>+		vsk->recvmsg_inq = psk->recvmsg_inq;
> 		security_sk_clone(parent, sk);
> 	} else {
> 		vsk->trusted = ns_capable_noaudit(&init_user_ns, CAP_NET_ADMIN);
>@@ -2014,6 +2015,66 @@ static void vsock_update_buffer_size(struct vsock_sock *vsk,
> 	vsk->buffer_size = val;
> }
>
>+static bool vsock_custom_sockopt(int optname)

Looking at the other function, what about vsock_sol_socket_custom()?

>+{
>+	switch (optname) {
>+	case SO_ZEROCOPY:
>+	case SO_INQ:
>+		return true;
>+	default:
>+		return false;
>+	}
>+}
>+
>+static int vsock_sol_socket_setsockopt(struct sock *sk, int optname,
>+				       sockptr_t optval, unsigned int optlen)
>+{
>+	struct vsock_sock *vsk = vsock_sk(sk);
>+	int err = 0;
>+	int val;
>+
>+	/* Use 'int' type here, because variable to

nit: why not using at least 80 columns for this comment?

>+	 * set these options usually has this type.
>+	 */
>+	if (optlen < sizeof(val))
>+		return -EINVAL;
>+
>+	if (copy_from_sockptr(&val, optval, sizeof(val)))
>+		return -EFAULT;
>+
>+	if (val < 0 || val > 1)
>+		return -EINVAL;

What about adding an helper with this code, and call it after checks for 
each SO_, in this way using SO_INQ on sock_dgram with 2 will return 
-ENOPROTOOPT.

Oh wait, we can use COPY_IN and duplicate the check in each place or add 
an helper just for that.

>+
>+	lock_sock(sk);
>+
>+	switch (optname) {
>+	case SO_ZEROCOPY:
>+		if (vsk->transport && !vsock_msgzerocopy_allow(vsk->transport)) {
>+			err = -EOPNOTSUPP;
>+			break;
>+		}
>+
>+		sock_valbool_flag(sk, SOCK_ZEROCOPY, val);
>+		break;
>+
>+	case SO_INQ:
>+		if (sk->sk_type != SOCK_STREAM) {
>+			err = -ENOPROTOOPT;
>+			break;
>+		}
>+
>+		vsk->recvmsg_inq = val;
>+		break;
>+
>+	default:
>+		err = -ENOPROTOOPT;
>+		break;
>+	}
>+
>+	release_sock(sk);
>+	return err;
>+}

Now it's much better, but we should not mix a refactoring with a new 
feature, so please split this patch in 2 patches, first one introducing 
vsock_sol_socket_setsockopt() just for SO_ZEROCOPY, second one 
introducing SO_INQ handling.

In this way, if we have to backport a fix to SO_ZEROCOPY handling in a 
stable branch, we can do it easily.

The rest LGTM,
Stefano

>+
> static int vsock_connectible_setsockopt(struct socket *sock,
> 					int level,
> 					int optname,
>@@ -2045,36 +2106,16 @@ static int vsock_connectible_setsockopt(struct socket *sock,
> 	sk = sock->sk;
> 	vsk = vsock_sk(sk);
>
>-	lock_sock(sk);
>-
>-	transport = vsk->transport;
>-
> 	if (level == SOL_SOCKET) {
>-		int zerocopy;
>-
>-		if (optname != SO_ZEROCOPY) {
>-			release_sock(sk);
>+		if (!vsock_custom_sockopt(optname))
> 			return sock_setsockopt(sock, level, optname, optval, optlen);
>-		}
>-
>-		/* Use 'int' type here, because variable to
>-		 * set this option usually has this type.
>-		 */
>-		COPY_IN(zerocopy);
>
>-		if (zerocopy < 0 || zerocopy > 1) {
>-			err = -EINVAL;
>-			goto exit;
>-		}
>+		return vsock_sol_socket_setsockopt(sk, optname, optval, optlen);
>+	}
>
>-		if (transport && !vsock_msgzerocopy_allow(transport)) {
>-			err = -EOPNOTSUPP;
>-			goto exit;
>-		}
>+	lock_sock(sk);
>
>-		sock_valbool_flag(sk, SOCK_ZEROCOPY, zerocopy);
>-		goto exit;
>-	}
>+	transport = vsk->transport;
>
> 	switch (optname) {
> 	case SO_VM_SOCKETS_BUFFER_SIZE:
>@@ -2581,6 +2622,7 @@ __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 +2679,26 @@ __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
>