On Mon, Dec 01, 2014 at 09:16:41AM +0100, David Hildenbrand wrote:

quoted

Based on patch by Cornelia Huck.

Note: for consistency, and to avoid sparse errors,
      convert all fields, even those no longer in use
      for virtio v1.0.

Signed-off-by: Cornelia Huck <redacted>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

...

quoted

-static unsigned int features[] = {
+static unsigned int features_legacy[] = {
 	VIRTIO_BLK_F_SEG_MAX, VIRTIO_BLK_F_SIZE_MAX, VIRTIO_BLK_F_GEOMETRY,
 	VIRTIO_BLK_F_RO, VIRTIO_BLK_F_BLK_SIZE, VIRTIO_BLK_F_SCSI,
 	VIRTIO_BLK_F_WCE, VIRTIO_BLK_F_TOPOLOGY, VIRTIO_BLK_F_CONFIG_WCE,
 	VIRTIO_BLK_F_MQ,
+}
+;
+static unsigned int features[] = {
+	VIRTIO_BLK_F_SEG_MAX, VIRTIO_BLK_F_SIZE_MAX, VIRTIO_BLK_F_GEOMETRY,
+	VIRTIO_BLK_F_RO, VIRTIO_BLK_F_BLK_SIZE,
+	VIRTIO_BLK_F_TOPOLOGY,
+	VIRTIO_BLK_F_MQ,
+	VIRTIO_F_VERSION_1,

We can fit this into less lines, like done for features_legacy.

I was asking myself if we could do the conversion of the statical values
somehow upfront, to reduce the patch size and avoid cpu_to_virtio.* at those
places.

Otherwise looks good to me.

I don't see how we can reduce the patch size.
For BE architectures it's dynamic, so at best the values
will become macros/incline functions taking a flag.

For some places on data path, it might be worth it
to cache the correct value e.g. as part of device
structure. This replaces a branch with a memory load,
so the gain would have to be measured, best done
separately?

-- 
MST