virtio: add VIRTIO_RING_NO_LEGACY

Add macro to disable legacy vring functions.
Signed-off-by: Matej Genci <matej.genci@nutanix.com>
Link: https://lore.kernel.org/r/20190911124942.243713-1-matej.genci@nutanix.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/virtio/virtio_pci_modern.c

@@ -16,6 +16,7 @@
 
 #include <linux/delay.h>
 #define VIRTIO_PCI_NO_LEGACY
+#define VIRTIO_RING_NO_LEGACY
 #include "virtio_pci_common.h"
 
 /*

include/uapi/linux/virtio_ring.h

@@ -135,6 +135,8 @@ struct vring {
 #define VRING_USED_ALIGN_SIZE 4
 #define VRING_DESC_ALIGN_SIZE 16
 
+#ifndef VIRTIO_RING_NO_LEGACY
+
 /* The standard layout for the ring is a continuous chunk of memory which looks
  * like this.  We assume num is a power of 2.
  *
@@ -181,6 +183,8 @@ static inline unsigned vring_size(unsigned int num, unsigned long align)
 		+ sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num;
 }
 
+#endif /* VIRTIO_RING_NO_LEGACY */
+
 /* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */
 /* Assuming a given event_idx value from the other side, if
  * we have just incremented index from old to new_idx,