vsock/test: Introduce vsock_wait_sent() helper

Distill the virtio_vsock_sock::bytes_unsent checking loop (ioctl SIOCOUTQ)
and move it to utils. Tweak the comment.

Signed-off-by: Michal Luczaj <mhal@rbox.co>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Link: https://patch.msgid.link/20250522-vsock-linger-v6-3-2ad00b0e447e@rbox.co
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: mmhal

tools/testing/vsock/util.c

@@ -17,6 +17,7 @@
 #include <assert.h>
 #include <sys/epoll.h>
 #include <sys/mman.h>
+#include <linux/sockios.h>
 
 #include "timeout.h"
 #include "control.h"
@@ -96,6 +97,30 @@ void vsock_wait_remote_close(int fd)
 	close(epollfd);
 }
 
+/* Wait until transport reports no data left to be sent.
+ * Return false if transport does not implement the unsent_bytes() callback.
+ */
+bool vsock_wait_sent(int fd)
+{
+	int ret, sock_bytes_unsent;
+
+	timeout_begin(TIMEOUT);
+	do {
+		ret = ioctl(fd, SIOCOUTQ, &sock_bytes_unsent);
+		if (ret < 0) {
+			if (errno == EOPNOTSUPP)
+				break;
+
+			perror("ioctl(SIOCOUTQ)");
+			exit(EXIT_FAILURE);
+		}
+		timeout_check("SIOCOUTQ");
+	} while (sock_bytes_unsent != 0);
+	timeout_end();
+
+	return !ret;
+}
+
 /* Create socket <type>, bind to <cid, port> and return the file descriptor. */
 int vsock_bind(unsigned int cid, unsigned int port, int type)
 {

tools/testing/vsock/util.h

@@ -54,6 +54,7 @@ int vsock_stream_listen(unsigned int cid, unsigned int port);
 int vsock_seqpacket_accept(unsigned int cid, unsigned int port,
 			   struct sockaddr_vm *clientaddrp);
 void vsock_wait_remote_close(int fd);
+bool vsock_wait_sent(int fd);
 void send_buf(int fd, const void *buf, size_t len, int flags,
 	      ssize_t expected_ret);
 void recv_buf(int fd, void *buf, size_t len, int flags, ssize_t expected_ret);

tools/testing/vsock/vsock_test.c

@@ -21,7 +21,6 @@
 #include <poll.h>
 #include <signal.h>
 #include <sys/ioctl.h>
-#include <linux/sockios.h>
 #include <linux/time64.h>
 
 #include "vsock_test_zerocopy.h"
@@ -1280,7 +1279,7 @@ static void test_unsent_bytes_server(const struct test_opts *opts, int type)
 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;
+	int fd;
 
 	fd = vsock_connect(opts->peer_cid, opts->peer_port, type);
 	if (fd < 0) {
@@ -1297,22 +1296,12 @@ static void test_unsent_bytes_client(const struct test_opts *opts, int type)
 	/* SIOCOUTQ isn't guaranteed to instantly track sent data. Even though
 	 * the "RECEIVED" message means that the other side has received the
 	 * data, there can be a delay in our kernel before updating the "unsent
-	 * bytes" counter. Repeat SIOCOUTQ until it returns 0.
+	 * bytes" counter. vsock_wait_sent() will repeat SIOCOUTQ until it
+	 * returns 0.
 	 */
-	timeout_begin(TIMEOUT);
-	do {
-		ret = ioctl(fd, SIOCOUTQ, &sock_bytes_unsent);
-		if (ret < 0) {
-			if (errno == EOPNOTSUPP) {
-				fprintf(stderr, "Test skipped, SIOCOUTQ not supported.\n");
-				break;
-			}
-			perror("ioctl");
-			exit(EXIT_FAILURE);
-		}
-		timeout_check("SIOCOUTQ");
-	} while (sock_bytes_unsent != 0);
-	timeout_end();
+	if (!vsock_wait_sent(fd))
+		fprintf(stderr, "Test skipped, SIOCOUTQ not supported.\n");
+
 	close(fd);
 }