[PATCH RFC v4 05/16] virtio: introduce legacy virtio devices

[Cornelia Huck <cornelia.huck@de.ibm.com>]

Introduce a helper function to indicate  whether a virtio device is
operating in legacy or virtio standard mode.

It may be used to make decisions about the endianess of virtio accesses
and other virtio-1 specific changes, enabling us to support transitional
devices.

Reviewed-by: Thomas Huth <thuth@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
---
 hw/virtio/virtio.c                |    6 +++++-
 include/hw/virtio/virtio-access.h |    4 ++++
 include/hw/virtio/virtio.h        |   13 +++++++++++--
 3 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 2eb5d3c..4149f45 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -883,7 +883,11 @@ static bool virtio_device_endian_needed(void *opaque)
     VirtIODevice *vdev = opaque;
 
     assert(vdev->device_endian != VIRTIO_DEVICE_ENDIAN_UNKNOWN);
-    return vdev->device_endian != virtio_default_endian();
+    if (virtio_device_is_legacy(vdev)) {
+        return vdev->device_endian != virtio_default_endian();
+    }
+    /* Devices conforming to VIRTIO 1.0 or later are always LE. */
+    return vdev->device_endian != VIRTIO_DEVICE_ENDIAN_LITTLE;
 }
 
 static const VMStateDescription vmstate_virtio_device_endian = {
diff --git a/include/hw/virtio/virtio-access.h b/include/hw/virtio/virtio-access.h
index 46456fd..c123ee0 100644
--- a/include/hw/virtio/virtio-access.h
+++ b/include/hw/virtio/virtio-access.h
@@ -19,6 +19,10 @@
 
 static inline bool virtio_access_is_big_endian(VirtIODevice *vdev)
 {
+    if (!virtio_device_is_legacy(vdev)) {
+        /* Devices conforming to VIRTIO 1.0 or later are always LE. */
+        return false;
+    }
 #if defined(TARGET_IS_BIENDIAN)
     return virtio_is_big_endian(vdev);
 #elif defined(TARGET_WORDS_BIGENDIAN)
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index b408166..40e567c 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -275,9 +275,18 @@ void virtio_queue_set_host_notifier_fd_handler(VirtQueue *vq, bool assign,
 void virtio_queue_notify_vq(VirtQueue *vq);
 void virtio_irq(VirtQueue *vq);
 
+static inline bool virtio_device_is_legacy(VirtIODevice *vdev)
+{
+    return !(vdev->guest_features[1] & (1 << (VIRTIO_F_VERSION_1 - 32)));
+}
+
 static inline bool virtio_is_big_endian(VirtIODevice *vdev)
 {
-    assert(vdev->device_endian != VIRTIO_DEVICE_ENDIAN_UNKNOWN);
-    return vdev->device_endian == VIRTIO_DEVICE_ENDIAN_BIG;
+    if (virtio_device_is_legacy(vdev)) {
+        assert(vdev->device_endian != VIRTIO_DEVICE_ENDIAN_UNKNOWN);
+        return vdev->device_endian == VIRTIO_DEVICE_ENDIAN_BIG;
+    }
+    /* Devices conforming to VIRTIO 1.0 or later are always LE. */
+    return false;
 }
 #endif
-- 
1.7.9.5