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>

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)
 {

tests/libqos/virtio.h

@@ -162,6 +162,11 @@ void qvirtio_set_driver_ok(const QVirtioBus *bus, QVirtioDevice *d);
 
 bool qvirtio_wait_queue_isr(const QVirtioBus *bus, QVirtioDevice *d,
                                             QVirtQueue *vq, uint64_t timeout);
+uint8_t qvirtio_wait_status_byte_no_isr(const QVirtioBus *bus,
+                                        QVirtioDevice *d,
+                                        QVirtQueue *vq,
+                                        uint64_t addr,
+                                        gint64 timeout_us);
 bool qvirtio_wait_config_isr(const QVirtioBus *bus, QVirtioDevice *d,
                                                             uint64_t timeout);
 QVirtQueue *qvirtqueue_setup(const QVirtioBus *bus, QVirtioDevice *d,

tests/virtio-blk-test.c

@@ -42,6 +42,7 @@
 
 #define TEST_IMAGE_SIZE         (64 * 1024 * 1024)
 #define QVIRTIO_BLK_TIMEOUT     100
+#define QVIRTIO_BLK_TIMEOUT_US  (30 * 1000 * 1000)
 #define PCI_SLOT                0x04
 #define PCI_FN                  0x00
 
@@ -595,10 +596,9 @@ static void pci_idx(void)
     qvirtqueue_kick(&qvirtio_pci, &dev->vdev, &vqpci->vq, free_head);
 
     /* No notification expected */
-    g_assert(!qvirtio_wait_queue_isr(&qvirtio_pci, &dev->vdev, &vqpci->vq,
-                                                        QVIRTIO_BLK_TIMEOUT));
-
-    status = readb(req_addr + 528);
+    status = qvirtio_wait_status_byte_no_isr(&qvirtio_pci, &dev->vdev,
+                                             &vqpci->vq, req_addr + 528,
+                                             QVIRTIO_BLK_TIMEOUT_US);
     g_assert_cmpint(status, ==, 0);
 
     guest_free(alloc, req_addr);