v4.19.13 snapshot.
diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
new file mode 100644
index 0000000..fab0213
--- /dev/null
+++ b/include/linux/virtio_ring.h
@@ -0,0 +1,115 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_VIRTIO_RING_H
+#define _LINUX_VIRTIO_RING_H
+
+#include <asm/barrier.h>
+#include <linux/irqreturn.h>
+#include <uapi/linux/virtio_ring.h>
+
+/*
+ * Barriers in virtio are tricky. Non-SMP virtio guests can't assume
+ * they're not on an SMP host system, so they need to assume real
+ * barriers. Non-SMP virtio hosts could skip the barriers, but does
+ * anyone care?
+ *
+ * For virtio_pci on SMP, we don't need to order with respect to MMIO
+ * accesses through relaxed memory I/O windows, so virt_mb() et al are
+ * sufficient.
+ *
+ * For using virtio to talk to real devices (eg. other heterogeneous
+ * CPUs) we do need real barriers. In theory, we could be using both
+ * kinds of virtio, so it's a runtime decision, and the branch is
+ * actually quite cheap.
+ */
+
+static inline void virtio_mb(bool weak_barriers)
+{
+ if (weak_barriers)
+ virt_mb();
+ else
+ mb();
+}
+
+static inline void virtio_rmb(bool weak_barriers)
+{
+ if (weak_barriers)
+ virt_rmb();
+ else
+ dma_rmb();
+}
+
+static inline void virtio_wmb(bool weak_barriers)
+{
+ if (weak_barriers)
+ virt_wmb();
+ else
+ dma_wmb();
+}
+
+static inline void virtio_store_mb(bool weak_barriers,
+ __virtio16 *p, __virtio16 v)
+{
+ if (weak_barriers) {
+ virt_store_mb(*p, v);
+ } else {
+ WRITE_ONCE(*p, v);
+ mb();
+ }
+}
+
+struct virtio_device;
+struct virtqueue;
+
+/*
+ * Creates a virtqueue and allocates the descriptor ring. If
+ * may_reduce_num is set, then this may allocate a smaller ring than
+ * expected. The caller should query virtqueue_get_ring_size to learn
+ * the actual size of the ring.
+ */
+struct virtqueue *vring_create_virtqueue(unsigned int index,
+ unsigned int num,
+ unsigned int vring_align,
+ struct virtio_device *vdev,
+ bool weak_barriers,
+ bool may_reduce_num,
+ bool ctx,
+ bool (*notify)(struct virtqueue *vq),
+ void (*callback)(struct virtqueue *vq),
+ const char *name);
+
+/* Creates a virtqueue with a custom layout. */
+struct virtqueue *__vring_new_virtqueue(unsigned int index,
+ struct vring vring,
+ struct virtio_device *vdev,
+ bool weak_barriers,
+ bool ctx,
+ bool (*notify)(struct virtqueue *),
+ void (*callback)(struct virtqueue *),
+ const char *name);
+
+/*
+ * Creates a virtqueue with a standard layout but a caller-allocated
+ * ring.
+ */
+struct virtqueue *vring_new_virtqueue(unsigned int index,
+ unsigned int num,
+ unsigned int vring_align,
+ struct virtio_device *vdev,
+ bool weak_barriers,
+ bool ctx,
+ void *pages,
+ bool (*notify)(struct virtqueue *vq),
+ void (*callback)(struct virtqueue *vq),
+ const char *name);
+
+/*
+ * Destroys a virtqueue. If created with vring_create_virtqueue, this
+ * also frees the ring.
+ */
+void vring_del_virtqueue(struct virtqueue *vq);
+
+/* Filter out transport-specific feature bits. */
+void vring_transport_features(struct virtio_device *vdev);
+
+irqreturn_t vring_interrupt(int irq, void *_vq);
+#endif /* _LINUX_VIRTIO_RING_H */