[PATCH v3 3/6] virtio: virtqueue_ordered_fill - VIRTIO_F_IN_ORDER support

[Jonah Palmer]

Add VIRTIO_F_IN_ORDER feature support for the virtqueue_fill operation.

The goal of the virtqueue_ordered_fill operation when the
VIRTIO_F_IN_ORDER feature has been negotiated is to search for this
now-used element, set its length, and mark the element as filled in
the VirtQueue's used_elems array.

By marking the element as filled, it will indicate that this element has
been processed and is ready to be flushed, so long as the element is
in-order.

Reviewed-by: Eugenio Pérez <eperezma@redhat.com>
Signed-off-by: Jonah Palmer <jonah.palmer@oracle.com>
---
 hw/virtio/virtio.c | 44 +++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 43 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 9cbf75f021..e1dfec4655 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -873,6 +873,46 @@ static void virtqueue_packed_fill(VirtQueue *vq, const 
VirtQueueElement *elem,
     vq->used_elems[idx].ndescs = elem->ndescs;
 }
 
+static void virtqueue_ordered_fill(VirtQueue *vq, const VirtQueueElement *elem,
+                                   unsigned int len)
+{
+    unsigned int i, steps, max_steps;
+
+    i = vq->used_idx;
+    steps = 0;
+    /*
+     * We shouldn't need to increase 'i' by more than the distance
+     * between used_idx and last_avail_idx.
+     */
+    max_steps = (vq->last_avail_idx - vq->used_idx) % vq->vring.num;
+
+    /* Search for element in vq->used_elems */
+    while (steps <= max_steps) {
+        /* Found element, set length and mark as filled */
+        if (vq->used_elems[i].index == elem->index) {
+            vq->used_elems[i].len = len;
+            vq->used_elems[i].in_order_filled = true;
+            break;
+        }
+
+        i += vq->used_elems[i].ndescs;
+        steps += vq->used_elems[i].ndescs;
+
+        if (i >= vq->vring.num) {
+            i -= vq->vring.num;
+        }
+    }
+
+    /*
+     * We should be able to find a matching VirtQueueElement in
+     * used_elems. If we don't, this is an error.
+     */
+    if (steps >= max_steps) {
+        qemu_log_mask(LOG_GUEST_ERROR, "%s: %s cannot fill buffer id %u\n",
+                      __func__, vdev->name, elem->index);
+    }
+}
+
 static void virtqueue_packed_fill_desc(VirtQueue *vq,
                                        const VirtQueueElement *elem,
                                        unsigned int idx,
@@ -923,7 +963,9 @@ void virtqueue_fill(VirtQueue *vq, const VirtQueueElement 
*elem,
         return;
     }
 
-    if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) {
+    if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_IN_ORDER)) {
+        virtqueue_ordered_fill(vq, elem, len);
+    } else if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) {
         virtqueue_packed_fill(vq, elem, len, idx);
     } else {
         virtqueue_split_fill(vq, elem, len, idx);
-- 
2.43.0