Since irq mode is determined dynamically on a per-device
basis, and virtio needs to know if using intx or msi-x,
make it a sysfs attribute.

--- a/lib/librte_eal/linuxapp/igb_uio/igb_uio.c
+++ b/lib/librte_eal/linuxapp/igb_uio/igb_uio.c
@@ -43,6 +43,10 @@
 	IGBUIO_MSIX_INTR_MODE
 };
 
+static const char *igbuio_intr_modes[] = {
+	"legacy", "msi", "msix"
+};
+
 /**
  * A structure describing the private information for a uio device.
  */
@@ -128,8 +132,20 @@
 }
 
 static DEVICE_ATTR(max_vfs, S_IRUGO | S_IWUSR, show_max_vfs, store_max_vfs);
+
+static ssize_t irq_mode_show(struct device *dev,
+			     struct device_attribute *attr, char *buf)
+{
+	struct uio_info *info = pci_get_drvdata(to_pci_dev(dev));
+	struct rte_uio_pci_dev *udev = igbuio_get_uio_pci_dev(info);
+
+	return sprintf(buf, "%s\n", igbuio_intr_modes[udev->mode]);
+}
+static DEVICE_ATTR(irq_mode, S_IRUGO, irq_mode_show, NULL);
+
 static struct attribute *dev_attrs[] = {
 	&dev_attr_max_vfs.attr,
+	&dev_attr_irq_mode.attr,
 	NULL,
 };