[PATCH v4 2/6] virtio: virtqueue_pop - VIRTIO_F_IN_ORDER support

[Jonah Palmer]

Add VIRTIO_F_IN_ORDER feature support in virtqueue_split_pop and
virtqueue_packed_pop.

VirtQueueElements popped from the available/descritpor ring are added to
the VirtQueue's used_elems array in-order and in the same fashion as
they would be added the used and descriptor rings, respectively.

This will allow us to keep track of the current order, what elements
have been written, as well as an element's essential data after being
processed.

Reviewed-by: Eugenio Pérez <eperezma@redhat.com>
Signed-off-by: Jonah Palmer <jonah.palmer@oracle.com>
---
last_avail_idx can grow well beyond vring.num, so for this reason we
need to keep the index bound between 0 and vring.num-1 for the split VQ
case.

 hw/virtio/virtio.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 583a224163..98eb601b09 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -1505,7 +1505,7 @@ static void *virtqueue_alloc_element(size_t sz, unsigned 
out_num, unsigned in_nu
 
 static void *virtqueue_split_pop(VirtQueue *vq, size_t sz)
 {
-    unsigned int i, head, max;
+    unsigned int i, head, max, idx;
     VRingMemoryRegionCaches *caches;
     MemoryRegionCache indirect_desc_cache;
     MemoryRegionCache *desc_cache;
@@ -1629,6 +1629,13 @@ static void *virtqueue_split_pop(VirtQueue *vq, size_t 
sz)
         elem->in_sg[i] = iov[out_num + i];
     }
 
+    if (virtio_vdev_has_feature(vdev, VIRTIO_F_IN_ORDER)) {
+        idx = (vq->last_avail_idx - 1) % vq->vring.num;
+        vq->used_elems[idx].index = elem->index;
+        vq->used_elems[idx].len = elem->len;
+        vq->used_elems[idx].ndescs = elem->ndescs;
+    }
+
     vq->inuse++;
 
     trace_virtqueue_pop(vq, elem, elem->in_num, elem->out_num);
@@ -1762,6 +1769,13 @@ static void *virtqueue_packed_pop(VirtQueue *vq, size_t 
sz)
 
     elem->index = id;
     elem->ndescs = (desc_cache == &indirect_desc_cache) ? 1 : elem_entries;
+
+    if (virtio_vdev_has_feature(vdev, VIRTIO_F_IN_ORDER)) {
+        vq->used_elems[vq->last_avail_idx].index = elem->index;
+        vq->used_elems[vq->last_avail_idx].len = elem->len;
+        vq->used_elems[vq->last_avail_idx].ndescs = elem->ndescs;
+    }
+
     vq->last_avail_idx += elem->ndescs;
     vq->inuse += elem->ndescs;
 
-- 
2.43.5