[PATCH net] vsock/test: Fix occasional failure in SIOCOUTQ tests

[Konstantin Shkolnyy <kshk@linux.ibm.com>]

These tests:
    "SOCK_STREAM ioctl(SIOCOUTQ) 0 unsent bytes"
    "SOCK_SEQPACKET ioctl(SIOCOUTQ) 0 unsent bytes"
output: "Unexpected 'SIOCOUTQ' value, expected 0, got 64 (CLIENT)".

They test that the SIOCOUTQ ioctl reports 0 unsent bytes after the data
have been received by the other side. However, sometimes there is a delay
in updating this "unsent bytes" counter, and the test fails even though
the counter properly goes to 0 several milliseconds later.

The delay occurs in the kernel because the used buffer notification
callback virtio_vsock_tx_done(), called upon receipt of the data by the
other side, doesn't update the counter itself. It delegates that to
a kernel thread (via vsock->tx_work). Sometimes that thread is delayed
more than the test expects.

Change the test to try SIOCOUTQ several times with small delays in between.

Signed-off-by: Konstantin Shkolnyy <kshk@linux.ibm.com>
---
 tools/testing/vsock/vsock_test.c | 26 ++++++++++++++++----------
 1 file changed, 16 insertions(+), 10 deletions(-)

diff --git a/tools/testing/vsock/vsock_test.c b/tools/testing/vsock/vsock_test.c
index d0f6d253ac72..143f1cba2d18 100644
--- a/tools/testing/vsock/vsock_test.c
+++ b/tools/testing/vsock/vsock_test.c
@@ -1264,21 +1264,27 @@ static void test_unsent_bytes_client(const struct test_opts *opts, int type)
 	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, SIOCOUTQ not supported.\n");
-		} else {
+	/* SIOCOUTQ isn't guaranteed to instantly track sent data */
+	for (int i = 0; i < 10; i++) {
+		ret = ioctl(fd, SIOCOUTQ, &sock_bytes_unsent);
+		if (ret == 0 && sock_bytes_unsent == 0)
+			goto success;
+
+		if (ret < 0) {
+			if (errno == EOPNOTSUPP) {
+				fprintf(stderr, "Test skipped, SIOCOUTQ not supported.\n");
+				goto success;
+			}
 			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);
+		usleep(10 * 1000);
 	}
 
+	fprintf(stderr, "Unexpected 'SIOCOUTQ' value, expected 0, got %i\n",
+		sock_bytes_unsent);
+	exit(EXIT_FAILURE);
+success:
 	close(fd);
 }
 
-- 
2.34.1