Linux Virtualization - Apr 2020 - [PATCH v7 11/19] virtio: add legacy init/size APIs

vring_init/vring_size (in the uapi directory) are kept
around to solely avoid breaking old userspace builds.
It's not actually part of the UAPI - it was kept in the UAPI
header by mistake, and using it in kernel isn't necessary
and prevents us from making changes safely.
In particular, the APIs actually assume the legacy layout.

Add an internal kernel-only vring_legacy_init/vring_legacy_size.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
 include/linux/virtio_ring.h | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
index c3f9ca054250..766d70bca492 100644
--- a/include/linux/virtio_ring.h
+++ b/include/linux/virtio_ring.h
@@ -140,4 +140,22 @@ void vring_del_virtqueue(struct virtqueue *vq);
 void vring_transport_features(struct virtio_device *vdev);
 
 irqreturn_t vring_interrupt(int irq, void *_vq);
+
+static inline void vring_legacy_init(struct vring *vr, unsigned int num, void
*p,
+				     unsigned long align)
+{
+	vr->num = num;
+	vr->desc = p;
+	vr->avail = (struct vring_avail *)((char *)p + num * sizeof(struct
vring_desc));
+	vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] +
sizeof(__virtio16)
+		+ align-1) & ~(align - 1));
+}
+
+static inline unsigned vring_legacy_size(unsigned int num, unsigned long align)
+{
+	return ((sizeof(struct vring_desc) * num + sizeof(__virtio16) * (3 + num)
+		 + align - 1) & ~(align - 1))
+		+ sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num;
+}
+
 #endif /* _LINUX_VIRTIO_RING_H */
-- 
MST