vfio-pci: Log device requests more verbosely

Log some clues indicating whether the user is receiving device
request interfaces or not listening.  This can help indicate why a
driver unbind is blocked or explain why QEMU automatically unplugged
a device from the VM.
Signed-off-by: NAlex Williamson <alex.williamson@redhat.com>

drivers/vfio/pci/vfio_pci.c

@@ -907,8 +907,14 @@ static void vfio_pci_request(void *device_data, unsigned int count)
 	mutex_lock(&vdev->igate);
 
 	if (vdev->req_trigger) {
-		dev_dbg(&vdev->pdev->dev, "Requesting device from user\n");
+		if (!(count % 10))
+			dev_notice_ratelimited(&vdev->pdev->dev,
+				"Relaying device request to user (#%u)\n",
+				count);
 		eventfd_signal(vdev->req_trigger, 1);
+	} else if (count == 0) {
+		dev_warn(&vdev->pdev->dev,
+			"No device request channel registered, blocked until released by user\n");
 	}
 
 	mutex_unlock(&vdev->igate);