@@ -139,7 +139,7 @@ int vsock_bind_connect(unsigned int cid, unsigned int port, unsigned int bind_po
 }
 
 /* Connect to <cid, port> and return the file descriptor. */
-static int vsock_connect(unsigned int cid, unsigned int port, int type)
+int vsock_connect(unsigned int cid, unsigned int port, int type)
 {
 	union {
 		struct sockaddr sa;

@@ -226,8 +226,8 @@ static int vsock_listen(unsigned int cid, unsigned int port, int type)
 /* Listen on <cid, port> and return the first incoming connection.  The remote
  * address is stored to clientaddrp.  clientaddrp may be NULL.
  */
-static int vsock_accept(unsigned int cid, unsigned int port,
-			struct sockaddr_vm *clientaddrp, int type)
+int vsock_accept(unsigned int cid, unsigned int port,
+		 struct sockaddr_vm *clientaddrp, int type)
 {
 	union {
 		struct sockaddr sa;

@@ -39,6 +39,9 @@ struct test_case {
 void init_signals(void);
 unsigned int parse_cid(const char *str);
 unsigned int parse_port(const char *str);
+int vsock_connect(unsigned int cid, unsigned int port, int type);
+int vsock_accept(unsigned int cid, unsigned int port,
+		 struct sockaddr_vm *clientaddrp, int type);
 int vsock_stream_connect(unsigned int cid, unsigned int port);
 int vsock_bind_connect(unsigned int cid, unsigned int port,
 		       unsigned int bind_port, int type);

@@ -20,6 +20,8 @@
 #include <sys/mman.h>
 #include <poll.h>
 #include <signal.h>
+#include <sys/ioctl.h>
+#include <linux/sockios.h>
 
 #include "vsock_test_zerocopy.h"
 #include "timeout.h"

@@ -1238,6 +1240,79 @@ static void test_double_bind_connect_client(const struct test_opts *opts)
 	}
 }
 
+#define MSG_BUF_IOCTL_LEN 64
+static void test_unsent_bytes_server(const struct test_opts *opts, int type)
+{
+	unsigned char buf[MSG_BUF_IOCTL_LEN];
+	int client_fd;
+
+	client_fd = vsock_accept(VMADDR_CID_ANY, 1234, NULL, type);
+	if (client_fd < 0) {
+		perror("accept");
+		exit(EXIT_FAILURE);
+	}
+
+	recv_buf(client_fd, buf, sizeof(buf), 0, sizeof(buf));
+	control_writeln("RECEIVED");
+
+	close(client_fd);
+}
+
+static void test_unsent_bytes_client(const struct test_opts *opts, int type)
+{
+	unsigned char buf[MSG_BUF_IOCTL_LEN];
+	int ret, fd, sock_bytes_unsent;
+
+	fd = vsock_connect(opts->peer_cid, 1234, type);
+	if (fd < 0) {
+		perror("connect");
+		exit(EXIT_FAILURE);
+	}
+
+	for (int i = 0; i < sizeof(buf); i++)
+		buf[i] = rand() & 0xFF;
+
+	send_buf(fd, buf, sizeof(buf), 0, sizeof(buf));
+	control_expectln("RECEIVED");
+
+	ret = ioctl(fd, SIOCOUTQ, &sock_bytes_unsent);
+	if (ret < 0) {
+		if (errno == EOPNOTSUPP) {
+			fprintf(stderr, "Test skipped\n");
+		} else {
+			perror("ioctl");
+			exit(EXIT_FAILURE);
+		}
+	} else if (ret == 0 && sock_bytes_unsent != 0) {
+		fprintf(stderr,
+			"Unexpected 'SIOCOUTQ' value, expected 0, got %i\n",
+			sock_bytes_unsent);
+		exit(EXIT_FAILURE);
+	}
+
+	close(fd);
+}
+
+static void test_stream_unsent_bytes_client(const struct test_opts *opts)
+{
+	test_unsent_bytes_client(opts, SOCK_STREAM);
+}
+
+static void test_stream_unsent_bytes_server(const struct test_opts *opts)
+{
+	test_unsent_bytes_server(opts, SOCK_STREAM);
+}
+
+static void test_seqpacket_unsent_bytes_client(const struct test_opts *opts)
+{
+	test_unsent_bytes_client(opts, SOCK_SEQPACKET);
+}
+
+static void test_seqpacket_unsent_bytes_server(const struct test_opts *opts)
+{
+	test_unsent_bytes_server(opts, SOCK_SEQPACKET);
+}
+
 #define RCVLOWAT_CREDIT_UPD_BUF_SIZE	(1024 * 128)
 /* This define is the same as in 'include/linux/virtio_vsock.h':
  * it is used to decide when to send credit update message during

@@ -1523,6 +1598,16 @@ static struct test_case test_cases[] = {
 		.run_client = test_stream_rcvlowat_def_cred_upd_client,
 		.run_server = test_stream_cred_upd_on_low_rx_bytes,
 	},
+	{
+		.name = "SOCK_STREAM ioctl(SIOCOUTQ) 0 unsent bytes",
+		.run_client = test_stream_unsent_bytes_client,
+		.run_server = test_stream_unsent_bytes_server,
+	},
+	{
+		.name = "SOCK_SEQPACKET ioctl(SIOCOUTQ) 0 unsent bytes",
+		.run_client = test_seqpacket_unsent_bytes_client,
+		.run_server = test_seqpacket_unsent_bytes_server,
+	},
 	{},
 };