libqos: improve event_index test with timeout

The virtio event_index feature lets the device driver tell the device
how many requests to process before raising the next interrupt.
virtio-blk-test.c tries to verify that the device does not raise an
interrupt unnecessarily.

Unfortunately the test has a race condition.  It spins checking for an
interrupt up to 100 times and then assumes the request has finished.  On
a slow host the I/O request could still be in flight and the test would
fail.

This patch waits for the request to complete, or until a 30-second
timeout is reached.  If an interrupt is raised while waiting the test
fails since the device was not supposed to raise interrupts.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 22 insertions, 0 deletions

diff --git a/tests/libqos/virtio.c b/tests/libqos/virtio.c
index 9b6de2c0a7..009325dd02 100644
--- a/tests/libqos/virtio.c
+++ b/tests/libqos/virtio.c
@@ -91,6 +91,28 @@ bool qvirtio_wait_queue_isr(const QVirtioBus *bus, QVirtioDevice *d,
     return timeout != 0;
 }
 
+/* Wait for the status byte at given guest memory address to be set
+ *
+ * The virtqueue interrupt must not be raised, making this useful for testing
+ * event_index functionality.
+ */
+uint8_t qvirtio_wait_status_byte_no_isr(const QVirtioBus *bus,
+                                        QVirtioDevice *d,
+                                        QVirtQueue *vq,
+                                        uint64_t addr,
+                                        gint64 timeout_us)
+{
+    gint64 start_time = g_get_monotonic_time();
+    uint8_t val;
+
+    while ((val = readb(addr)) == 0xff) {
+        clock_step(100);
+        g_assert(!bus->get_queue_isr_status(d, vq));
+        g_assert(g_get_monotonic_time() - start_time <= timeout_us);
+    }
+    return val;
+}
+
 bool qvirtio_wait_config_isr(const QVirtioBus *bus, QVirtioDevice *d,
                                                             uint64_t timeout)
 {