wqueue: Reject messges if queue is considered full

The write queue was always meant to not queue more than the
max_length messages but the implementation never rejected a
message.

Begin to log and enforce the queue size limit, add a testcase
to verify the code and initialize except_cb as part of a fix
for that new test case.

Real applications might now run into the queue limit and drop
messages where they just queued them before. It is unfortunate
but I still think it is good to implement the routine as it was
intended. We need to review osmo_wqueue_enqueue once more to
see that no msgb is leaked.

Change-Id: I1e6aef30f3e73d4bcf2967bc49f0783aa65395ae

2 files changed, 82 insertions, 0 deletions

diff --git a/tests/write_queue/wqueue_test.c b/tests/write_queue/wqueue_test.c
new file mode 100644
index 00000000..827e4e84
--- /dev/null
+++ b/tests/write_queue/wqueue_test.c
@@ -0,0 +1,81 @@
+#include <osmocom/core/logging.h>
+#include <osmocom/core/utils.h>
+#include <osmocom/core/write_queue.h>
+
+static const struct log_info_cat default_categories[] = {
+};
+
+static const struct log_info log_info = {
+	.cat = default_categories,
+	.num_cat = ARRAY_SIZE(default_categories),
+};
+
+static void test_wqueue_limit(void)
+{
+	struct msgb *msg;
+	struct osmo_wqueue wqueue;
+	int rc;
+
+	osmo_wqueue_init(&wqueue, 0);
+	OSMO_ASSERT(wqueue.max_length == 0);
+	OSMO_ASSERT(wqueue.current_length == 0);
+	OSMO_ASSERT(wqueue.read_cb == NULL);
+	OSMO_ASSERT(wqueue.write_cb == NULL);
+	OSMO_ASSERT(wqueue.except_cb == NULL);
+
+	/* try to add and fail */
+	msg = msgb_alloc(4096, "msg1");
+	rc = osmo_wqueue_enqueue(&wqueue, msg);
+	OSMO_ASSERT(rc < 0);
+
+	/* add one and fail on the second */
+	wqueue.max_length = 1;
+	rc = osmo_wqueue_enqueue(&wqueue, msg);
+	OSMO_ASSERT(rc == 0);
+	OSMO_ASSERT(wqueue.current_length == 1);
+	msg = msgb_alloc(4096, "msg2");
+	rc = osmo_wqueue_enqueue(&wqueue, msg);
+	OSMO_ASSERT(rc < 0);
+
+	/* add one more */
+	wqueue.max_length = 2;
+	rc = osmo_wqueue_enqueue(&wqueue, msg);
+	OSMO_ASSERT(rc == 0);
+	OSMO_ASSERT(wqueue.current_length == 2);
+
+	/* release everything */
+	osmo_wqueue_clear(&wqueue);
+	OSMO_ASSERT(wqueue.current_length == 0);
+	OSMO_ASSERT(wqueue.max_length == 2);
+
+	/* Add two, fail on the third, free it and the queue */
+	msg = msgb_alloc(4096, "msg3");
+	rc = osmo_wqueue_enqueue(&wqueue, msg);
+	OSMO_ASSERT(rc == 0);
+	OSMO_ASSERT(wqueue.current_length == 1);
+	msg = msgb_alloc(4096, "msg4");
+	rc = osmo_wqueue_enqueue(&wqueue, msg);
+	OSMO_ASSERT(rc == 0);
+	OSMO_ASSERT(wqueue.current_length == 2);
+	msg = msgb_alloc(4096, "msg5");
+	rc = osmo_wqueue_enqueue(&wqueue, msg);
+	OSMO_ASSERT(rc < 0);
+	OSMO_ASSERT(wqueue.current_length == 2);
+	msgb_free(msg);
+	osmo_wqueue_clear(&wqueue);
+}
+
+int main(int argc, char **argv)
+{
+	struct log_target *stderr_target;
+
+	log_init(&log_info, NULL);
+	stderr_target = log_target_create_stderr();
+	log_add_target(stderr_target);
+	log_set_print_filename(stderr_target, 0);
+
+	test_wqueue_limit();
+
+	printf("Done\n");
+	return 0;
+}
diff --git a/tests/write_queue/wqueue_test.ok b/tests/write_queue/wqueue_test.ok
new file mode 100644
index 00000000..a965a70e
--- /dev/null
+++ b/tests/write_queue/wqueue_test.ok
@@ -0,0 +1 @@
+Done