[PATCH net-next 0/2] vsock: SO_INQ for stream sockets

[PATCH net-next 0/2] vsock: SO_INQ for stream sockets

[David Carlier]

This is the follow-up announced in the receive queue hint series [1]:
SO_INQ and SCM_INQ for AF_VSOCK stream sockets, as AF_UNIX has.

The value is the one SIOCINQ returns, so on Hyper-V it covers the
current packet only. The flag is per socket, is not inherited by
accepted sockets, and the sockmap receive path does not report it.

Tested over loopback with vsock_test and vsock_uring_test.

[1] https://lore.kernel.org/netdev/20260923184008.153541-1-devnexen@gmail.com/

David Carlier (2):
  vsock: support SO_INQ on stream sockets
  vsock/test: cover SO_INQ

 include/net/af_vsock.h           |   1 +
 net/vmw_vsock/af_vsock.c         |  41 +++++--
 tools/testing/vsock/vsock_test.c | 191 +++++++++++++++++++++++++++++++
 3 files changed, 224 insertions(+), 9 deletions(-)


base-commit: a4057f51efc2b74ddf46721e83f45e9efb13649d
-- 
2.55.0

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

[David Carlier]

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

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

[sashiko-bot]

> 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>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261012235524.41468-1-devnexen@gmail.com?part=1

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

[Stefano Garzarella]

On Tue, Oct 13, 2026 at 12:55:23AM +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. 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;

Please use a variable with a better name. 

>
>-		if (optname != SO_ZEROCOPY) {
>+		if (optname != SO_ZEROCOPY && optname != SO_INQ) {

Can we add something like unix_custom_sockopt()?

> 			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;

Should child sockets inherit this from a listener socket?

>+			goto exit;
>+		}

Please add a switch to handle SO_INQ and SO_ZEROCOPY clearly.

>+
> 		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;
> 	}

Maybe we can add a new function to handle SOL_SOCKET level, but I don't 
have a strong opinion on that.

>
>@@ -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 &&

Is the bitwise or what we want here?

Thanks,
Stefano

>+	    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
>

[PATCH net-next 2/2] vsock/test: cover SO_INQ

[David Carlier]

Check the SCM_INQ value after a partial receive, after draining the
queue and at EOF, that no cmsg is sent while the option is off, and
that out of range values and SOCK_SEQPACKET are rejected.

Signed-off-by: David Carlier <devnexen@gmail.com>
---
 tools/testing/vsock/vsock_test.c | 191 +++++++++++++++++++++++++++++++
 1 file changed, 191 insertions(+)

diff --git a/tools/testing/vsock/vsock_test.c b/tools/testing/vsock/vsock_test.c
index b4ff9f946565..00bb68c00c07 100644
--- a/tools/testing/vsock/vsock_test.c
+++ b/tools/testing/vsock/vsock_test.c
@@ -2429,6 +2429,188 @@ static void test_stream_collapse_server(const struct test_opts *opts)
 	close(fd);
 }
 
+#define SO_INQ_BUF_LEN 64
+#define SO_INQ_CHUNK_LEN 16
+
+static int so_inq_set(int fd, int val)
+{
+	return setsockopt(fd, SOL_SOCKET, SO_INQ, &val, sizeof(val));
+}
+
+/* Receive @len bytes and return the SCM_INQ value, or -1 if the kernel did
+ * not attach one.
+ */
+static int so_inq_recv(int fd, size_t len, int expected_ret)
+{
+	char control[CMSG_SPACE(sizeof(int))] = { 0 };
+	unsigned char buf[SO_INQ_BUF_LEN];
+	struct iovec iov = {
+		.iov_base = buf,
+		.iov_len = len,
+	};
+	struct msghdr msg = {
+		.msg_iov = &iov,
+		.msg_iovlen = 1,
+		.msg_control = control,
+		.msg_controllen = sizeof(control),
+	};
+	struct cmsghdr *cmsg;
+	ssize_t ret;
+	int inq;
+
+	ret = recvmsg(fd, &msg, 0);
+	if (ret < 0) {
+		perror("recvmsg");
+		exit(EXIT_FAILURE);
+	}
+
+	expect_res(ret, expected_ret, "recvmsg");
+
+	for (cmsg = CMSG_FIRSTHDR(&msg); cmsg; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
+		if (cmsg->cmsg_level != SOL_SOCKET ||
+		    cmsg->cmsg_type != SCM_INQ)
+			continue;
+
+		memcpy(&inq, CMSG_DATA(cmsg), sizeof(inq));
+		return inq;
+	}
+
+	return -1;
+}
+
+static void test_stream_so_inq_client(const struct test_opts *opts)
+{
+	int fd;
+
+	fd = vsock_stream_connect(opts->peer_cid, opts->peer_port);
+	if (fd < 0) {
+		perror("connect");
+		exit(EXIT_FAILURE);
+	}
+
+	control_expectln("SENT");
+
+	/* Wait for the whole payload to be queued, so the values below do not
+	 * depend on how the transport delivers it.
+	 */
+	if (!vsock_ioctl_int(fd, SIOCINQ, SO_INQ_BUF_LEN)) {
+		fprintf(stderr, "Test skipped, SIOCINQ not supported.\n");
+		goto out;
+	}
+
+	/* No ancillary data unless the option is enabled. */
+	expect_res(so_inq_recv(fd, SO_INQ_CHUNK_LEN, SO_INQ_CHUNK_LEN), -1,
+		   "SCM_INQ with SO_INQ disabled");
+
+	if (so_inq_set(fd, 1)) {
+		if (errno != ENOPROTOOPT) {
+			perror("setsockopt(SO_INQ)");
+			exit(EXIT_FAILURE);
+		}
+
+		fprintf(stderr, "Test skipped, SO_INQ not supported.\n");
+		goto out;
+	}
+
+	/* Partial read: the rest of the payload is still queued. */
+	expect_res(so_inq_recv(fd, SO_INQ_CHUNK_LEN, SO_INQ_CHUNK_LEN),
+		   SO_INQ_BUF_LEN - 2 * SO_INQ_CHUNK_LEN,
+		   "SCM_INQ after partial receive");
+
+	/* Draining read while the peer stays connected. */
+	expect_res(so_inq_recv(fd, SO_INQ_BUF_LEN - 2 * SO_INQ_CHUNK_LEN,
+			       SO_INQ_BUF_LEN - 2 * SO_INQ_CHUNK_LEN), 0,
+		   "SCM_INQ after draining receive");
+
+	control_writeln("DRAINED");
+	vsock_wait_remote_close(fd);
+
+	/* Nothing is queued once the peer is gone, but 1 is reported so the
+	 * caller keeps reading until it observes EOF, as TCP_INQ does.
+	 */
+	expect_res(so_inq_recv(fd, SO_INQ_CHUNK_LEN, 0), 1, "SCM_INQ at EOF");
+
+	if (so_inq_set(fd, 0)) {
+		perror("setsockopt(SO_INQ)");
+		exit(EXIT_FAILURE);
+	}
+
+	expect_res(so_inq_recv(fd, SO_INQ_CHUNK_LEN, 0), -1,
+		   "SCM_INQ after disabling SO_INQ");
+
+	close(fd);
+	return;
+
+out:
+	control_writeln("DRAINED");
+	close(fd);
+}
+
+static void test_stream_so_inq_server(const struct test_opts *opts)
+{
+	unsigned char buf[SO_INQ_BUF_LEN];
+	int fd;
+
+	fd = vsock_stream_accept(VMADDR_CID_ANY, opts->peer_port, NULL);
+	if (fd < 0) {
+		perror("accept");
+		exit(EXIT_FAILURE);
+	}
+
+	memset(buf, 'A', sizeof(buf));
+	send_buf(fd, buf, sizeof(buf), 0, sizeof(buf));
+	control_writeln("SENT");
+
+	/* Keep the connection open until the peer has drained the queue: an
+	 * early close would turn its last SCM_INQ value into the EOF one.
+	 */
+	control_expectln("DRAINED");
+	close(fd);
+}
+
+static void test_so_inq_validation_client(const struct test_opts *opts)
+{
+	int fd;
+
+	fd = socket(AF_VSOCK, SOCK_STREAM, 0);
+	if (fd < 0) {
+		perror("socket");
+		exit(EXIT_FAILURE);
+	}
+
+	if (so_inq_set(fd, 1)) {
+		if (errno != ENOPROTOOPT) {
+			perror("setsockopt(SO_INQ)");
+			exit(EXIT_FAILURE);
+		}
+
+		fprintf(stderr, "Test skipped, SO_INQ not supported.\n");
+		close(fd);
+		return;
+	}
+
+	if (!so_inq_set(fd, 2) || errno != EINVAL) {
+		fprintf(stderr, "SO_INQ accepted an out of range value\n");
+		exit(EXIT_FAILURE);
+	}
+
+	close(fd);
+
+	/* SCM_INQ counts bytes, which a message based socket cannot report. */
+	fd = socket(AF_VSOCK, SOCK_SEQPACKET, 0);
+	if (fd < 0) {
+		perror("socket");
+		exit(EXIT_FAILURE);
+	}
+
+	if (!so_inq_set(fd, 1) || errno != ENOPROTOOPT) {
+		fprintf(stderr, "SO_INQ not rejected on SOCK_SEQPACKET\n");
+		exit(EXIT_FAILURE);
+	}
+
+	close(fd);
+}
+
 static struct test_case test_cases[] = {
 	{
 		.name = "SOCK_STREAM connection reset",
@@ -2633,6 +2815,15 @@ static struct test_case test_cases[] = {
 		.run_client = test_stream_collapse_client,
 		.run_server = test_stream_collapse_server,
 	},
+	{
+		.name = "SOCK_STREAM SO_INQ functionality",
+		.run_client = test_stream_so_inq_client,
+		.run_server = test_stream_so_inq_server,
+	},
+	{
+		.name = "SO_INQ option validation",
+		.run_client = test_so_inq_validation_client,
+	},
 	{},
 };
 
-- 
2.55.0

Re: [PATCH net-next 2/2] vsock/test: cover SO_INQ

[sashiko-bot]

> Check the SCM_INQ value after a partial receive, after draining the
> queue and at EOF, that no cmsg is sent while the option is off, and
> that out of range values and SOCK_SEQPACKET are rejected.
> 
> Signed-off-by: David Carlier <devnexen@gmail.com>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261012235524.41468-1-devnexen@gmail.com?part=2

Re: [PATCH net-next 2/2] vsock/test: cover SO_INQ

[Stefano Garzarella]

On Tue, Oct 13, 2026 at 12:55:24AM +0100, David Carlier wrote:
>Check the SCM_INQ value after a partial receive, after draining the
>queue and at EOF, that no cmsg is sent while the option is off, and
>that out of range values and SOCK_SEQPACKET are rejected.
>
>Signed-off-by: David Carlier <devnexen@gmail.com>
>---
> tools/testing/vsock/vsock_test.c | 191 +++++++++++++++++++++++++++++++
> 1 file changed, 191 insertions(+)
>
>diff --git a/tools/testing/vsock/vsock_test.c b/tools/testing/vsock/vsock_test.c
>index b4ff9f946565..00bb68c00c07 100644
>--- a/tools/testing/vsock/vsock_test.c
>+++ b/tools/testing/vsock/vsock_test.c
>@@ -2429,6 +2429,188 @@ static void test_stream_collapse_server(const struct test_opts *opts)
> 	close(fd);
> }
>
>+#define SO_INQ_BUF_LEN 64
>+#define SO_INQ_CHUNK_LEN 16
>+
>+static int so_inq_set(int fd, int val)
>+{
>+	return setsockopt(fd, SOL_SOCKET, SO_INQ, &val, sizeof(val));
>+}
>+
>+/* Receive @len bytes and return the SCM_INQ value, or -1 if the kernel did
>+ * not attach one.
>+ */
>+static int so_inq_recv(int fd, size_t len, int expected_ret)
>+{
>+	char control[CMSG_SPACE(sizeof(int))] = { 0 };
>+	unsigned char buf[SO_INQ_BUF_LEN];
>+	struct iovec iov = {
>+		.iov_base = buf,
>+		.iov_len = len,
>+	};
>+	struct msghdr msg = {
>+		.msg_iov = &iov,
>+		.msg_iovlen = 1,
>+		.msg_control = control,
>+		.msg_controllen = sizeof(control),
>+	};
>+	struct cmsghdr *cmsg;
>+	ssize_t ret;
>+	int inq;
>+
>+	ret = recvmsg(fd, &msg, 0);
>+	if (ret < 0) {
>+		perror("recvmsg");
>+		exit(EXIT_FAILURE);
>+	}
>+
>+	expect_res(ret, expected_ret, "recvmsg");
>+
>+	for (cmsg = CMSG_FIRSTHDR(&msg); cmsg; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
>+		if (cmsg->cmsg_level != SOL_SOCKET ||
>+		    cmsg->cmsg_type != SCM_INQ)
>+			continue;

Should we check CMSG_LEN and/or MSG_CTRUNC ?

The rest LGTM.

Thanks,
Stefano

>+
>+		memcpy(&inq, CMSG_DATA(cmsg), sizeof(inq));
>+		return inq;
>+	}
>+
>+	return -1;
>+}
>+
>+static void test_stream_so_inq_client(const struct test_opts *opts)
>+{
>+	int fd;
>+
>+	fd = vsock_stream_connect(opts->peer_cid, opts->peer_port);
>+	if (fd < 0) {
>+		perror("connect");
>+		exit(EXIT_FAILURE);
>+	}
>+
>+	control_expectln("SENT");
>+
>+	/* Wait for the whole payload to be queued, so the values below do not
>+	 * depend on how the transport delivers it.
>+	 */
>+	if (!vsock_ioctl_int(fd, SIOCINQ, SO_INQ_BUF_LEN)) {
>+		fprintf(stderr, "Test skipped, SIOCINQ not supported.\n");
>+		goto out;
>+	}
>+
>+	/* No ancillary data unless the option is enabled. */
>+	expect_res(so_inq_recv(fd, SO_INQ_CHUNK_LEN, SO_INQ_CHUNK_LEN), -1,
>+		   "SCM_INQ with SO_INQ disabled");
>+
>+	if (so_inq_set(fd, 1)) {
>+		if (errno != ENOPROTOOPT) {
>+			perror("setsockopt(SO_INQ)");
>+			exit(EXIT_FAILURE);
>+		}
>+
>+		fprintf(stderr, "Test skipped, SO_INQ not supported.\n");
>+		goto out;
>+	}
>+
>+	/* Partial read: the rest of the payload is still queued. */
>+	expect_res(so_inq_recv(fd, SO_INQ_CHUNK_LEN, SO_INQ_CHUNK_LEN),
>+		   SO_INQ_BUF_LEN - 2 * SO_INQ_CHUNK_LEN,
>+		   "SCM_INQ after partial receive");
>+
>+	/* Draining read while the peer stays connected. */
>+	expect_res(so_inq_recv(fd, SO_INQ_BUF_LEN - 2 * SO_INQ_CHUNK_LEN,
>+			       SO_INQ_BUF_LEN - 2 * SO_INQ_CHUNK_LEN), 0,
>+		   "SCM_INQ after draining receive");
>+
>+	control_writeln("DRAINED");
>+	vsock_wait_remote_close(fd);
>+
>+	/* Nothing is queued once the peer is gone, but 1 is reported so the
>+	 * caller keeps reading until it observes EOF, as TCP_INQ does.
>+	 */
>+	expect_res(so_inq_recv(fd, SO_INQ_CHUNK_LEN, 0), 1, "SCM_INQ at EOF");
>+
>+	if (so_inq_set(fd, 0)) {
>+		perror("setsockopt(SO_INQ)");
>+		exit(EXIT_FAILURE);
>+	}
>+
>+	expect_res(so_inq_recv(fd, SO_INQ_CHUNK_LEN, 0), -1,
>+		   "SCM_INQ after disabling SO_INQ");
>+
>+	close(fd);
>+	return;
>+
>+out:
>+	control_writeln("DRAINED");
>+	close(fd);
>+}
>+
>+static void test_stream_so_inq_server(const struct test_opts *opts)
>+{
>+	unsigned char buf[SO_INQ_BUF_LEN];
>+	int fd;
>+
>+	fd = vsock_stream_accept(VMADDR_CID_ANY, opts->peer_port, NULL);
>+	if (fd < 0) {
>+		perror("accept");
>+		exit(EXIT_FAILURE);
>+	}
>+
>+	memset(buf, 'A', sizeof(buf));
>+	send_buf(fd, buf, sizeof(buf), 0, sizeof(buf));
>+	control_writeln("SENT");
>+
>+	/* Keep the connection open until the peer has drained the queue: an
>+	 * early close would turn its last SCM_INQ value into the EOF one.
>+	 */
>+	control_expectln("DRAINED");
>+	close(fd);
>+}
>+
>+static void test_so_inq_validation_client(const struct test_opts *opts)
>+{
>+	int fd;
>+
>+	fd = socket(AF_VSOCK, SOCK_STREAM, 0);
>+	if (fd < 0) {
>+		perror("socket");
>+		exit(EXIT_FAILURE);
>+	}
>+
>+	if (so_inq_set(fd, 1)) {
>+		if (errno != ENOPROTOOPT) {
>+			perror("setsockopt(SO_INQ)");
>+			exit(EXIT_FAILURE);
>+		}
>+
>+		fprintf(stderr, "Test skipped, SO_INQ not supported.\n");
>+		close(fd);
>+		return;
>+	}
>+
>+	if (!so_inq_set(fd, 2) || errno != EINVAL) {
>+		fprintf(stderr, "SO_INQ accepted an out of range value\n");
>+		exit(EXIT_FAILURE);
>+	}
>+
>+	close(fd);
>+
>+	/* SCM_INQ counts bytes, which a message based socket cannot report. */
>+	fd = socket(AF_VSOCK, SOCK_SEQPACKET, 0);
>+	if (fd < 0) {
>+		perror("socket");
>+		exit(EXIT_FAILURE);
>+	}
>+
>+	if (!so_inq_set(fd, 1) || errno != ENOPROTOOPT) {
>+		fprintf(stderr, "SO_INQ not rejected on SOCK_SEQPACKET\n");
>+		exit(EXIT_FAILURE);
>+	}
>+
>+	close(fd);
>+}
>+
> static struct test_case test_cases[] = {
> 	{
> 		.name = "SOCK_STREAM connection reset",
>@@ -2633,6 +2815,15 @@ static struct test_case test_cases[] = {
> 		.run_client = test_stream_collapse_client,
> 		.run_server = test_stream_collapse_server,
> 	},
>+	{
>+		.name = "SOCK_STREAM SO_INQ functionality",
>+		.run_client = test_stream_so_inq_client,
>+		.run_server = test_stream_so_inq_server,
>+	},
>+	{
>+		.name = "SO_INQ option validation",
>+		.run_client = test_so_inq_validation_client,
>+	},
> 	{},
> };
>
>-- 
>2.55.0
>