virtio: Put entries in freelist in reverse order

This avoids breaking krw@'s ongoing work on improving virtio_enqueue_trim().

diff --git a/sys/dev/pv/virtio.c b/sys/dev/pv/virtio.c
index 8d1fb46..9dee3fb 100644 (file)
--- a/sys/dev/pv/virtio.c
+++ b/sys/dev/pv/virtio.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: virtio.c,v 1.6 2017/05/30 08:35:32 sf Exp $   */
+/*     $OpenBSD: virtio.c,v 1.7 2017/05/30 11:02:39 sf Exp $   */
 /*     $NetBSD: virtio.c,v 1.3 2011/11/02 23:05:52 njoly Exp $ */
 
 /*
@@ -257,7 +257,11 @@ virtio_init_vq(struct virtio_softc *sc, struct virtqueue *vq, int reinit)
 
        /* free slot management */
        SLIST_INIT(&vq->vq_freelist);
-       for (i = 0; i < vq_size; i++) {
+       /*
+        * virtio_enqueue_trim needs monotonely raising entries, therefore
+        * initialize in reverse order
+        */
+       for (i = vq_size - 1; i >= 0; i--) {
                SLIST_INSERT_HEAD(&vq->vq_freelist, &vq->vq_entries[i],
                    qe_list);
                vq->vq_entries[i].qe_index = i;