tests: Ensure that overflow test always overflows

While the default Unix socket buffer size on Linux is relatively
small, on some computers the default size may be configured to
be huge, making the overflow test never actually overflow the
Wayland display socket.

The changed code now explicitly sets the display socket send buffer
size to be small enough to guarantee an overflow.

Signed-off-by: Manuel Stoeckl <code@mstoeckl.com>

1 files changed, 9 insertions, 3 deletions

diff --git a/tests/display-test.c b/tests/display-test.c
index f155d08..3db7c95 100644
--- a/tests/display-test.c
+++ b/tests/display-test.c
@@ -1430,13 +1430,19 @@ send_overflow_client(void *data)
 	int i, err = 0;
 	int *pipes = data;
 	char tmp = '\0';
+	int sock, optval = 16384;
+
+	/* Limit the send buffer size for the display socket to guarantee
+	 * that the test will cause an overflow. */
+	sock = wl_display_get_fd(c->wl_display);
+	assert(setsockopt(sock, SOL_SOCKET, SO_SNDBUF, &optval, sizeof(optval)) == 0);
 
 	/* Request to break out of 'display_run' in the main process */
 	assert(stop_display(c, 1) >= 0);
 
-	/* On Linux, the Unix socket default buffer size is <=256KB, and
-	 * each noop request requires 8 bytes; the buffer should thus
-	 * overflow within about 32K /unhandled/ iterations */
+	/* On Linux, the actual socket data + metadata space is twice `optval`;
+	 * since each noop request requires 8 bytes, the buffer should overflow
+	 * within <=4096 iterations. */
 	for (i = 0; i < 1000000; i++) {
 		noop_request(c);
 		err = wl_display_get_error(c->wl_display);