[Qemu-devel] [PATCH 2/2] virtio-balloon: virtio 1 support

[Michael S. Tsirkin]

Virtio 1.0 doesn't include a modern balloon device.  At some point we'll
likely define an incompatible interface with a different ID and
different semantics.  But for now, it's not a big effort to support a
transitional balloon device: this has the advantage of supporting
existing drivers, transparently, as well as transports that don't allow
mixing virtio 0 and virtio 1 devices. And balloon is an easy device to
test, so it's also useful for people to test virtio core handling of
transitional devices.

The only interface issue is with the stats buffer, which has misaligned
fields. We could leave it as is, but this sets a bad precedent that
others might copy by mistake.

Signed-off-by: Michael S. Tsirkin <address@hidden>
---
 hw/virtio/virtio-balloon.c | 31 +++++++++++++++++++++++--------
 1 file changed, 23 insertions(+), 8 deletions(-)

diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
index d2d7c3e..568a008 100644
--- a/hw/virtio/virtio-balloon.c
+++ b/hw/virtio/virtio-balloon.c
@@ -239,7 +239,8 @@ static void virtio_balloon_receive_stats(VirtIODevice 
*vdev, VirtQueue *vq)
 {
     VirtIOBalloon *s = VIRTIO_BALLOON(vdev);
     VirtQueueElement *elem = &s->stats_vq_elem;
-    VirtIOBalloonStat stat;
+    VirtIOBalloonStat legacy_stat;
+    VirtIOBalloonStatModern modern_stat;
     size_t offset = 0;
     qemu_timeval tv;
 
@@ -253,14 +254,28 @@ static void virtio_balloon_receive_stats(VirtIODevice 
*vdev, VirtQueue *vq)
      */
     reset_stats(s);
 
-    while (iov_to_buf(elem->out_sg, elem->out_num, offset, &stat, sizeof(stat))
-           == sizeof(stat)) {
-        uint16_t tag = virtio_tswap16(vdev, stat.tag);
-        uint64_t val = virtio_tswap64(vdev, stat.val);
+    if (virtio_has_feature(vdev, VIRTIO_F_VERSION_1)) {
+        while (iov_to_buf(elem->out_sg, elem->out_num, offset,
+                          &modern_stat, sizeof(modern_stat))
+               == sizeof(modern_stat)) {
+            uint16_t tag = le16_to_cpu(modern_stat.tag);
+            uint64_t val = le64_to_cpu(modern_stat.val);
 
-        offset += sizeof(stat);
-        if (tag < VIRTIO_BALLOON_S_NR)
-            s->stats[tag] = val;
+            offset += sizeof(modern_stat);
+            if (tag < VIRTIO_BALLOON_S_NR)
+                s->stats[tag] = val;
+        }
+    } else {
+        while (iov_to_buf(elem->out_sg, elem->out_num, offset,
+                          &legacy_stat, sizeof(legacy_stat))
+               == sizeof(legacy_stat)) {
+            uint16_t tag = virtio_tswap16(vdev, legacy_stat.tag);
+            uint64_t val = virtio_tswap64(vdev, legacy_stat.val);
+
+            offset += sizeof(legacy_stat);
+            if (tag < VIRTIO_BALLOON_S_NR)
+                s->stats[tag] = val;
+        }
     }
     s->stats_vq_offset = offset;
 
-- 
MST