virtio: Add transport feature handling stub for virtio_ring.

To prepare for virtio_ring transport feature bits, hook in a call in
all the users to manipulate them.  This currently just clears all the
bits, since it doesn't understand any features.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

2 files changed, 19 insertions, 0 deletions

diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c
index 9855975a72a3..c7dc37c7cce9 100644
--- a/drivers/virtio/virtio_pci.c
+++ b/drivers/virtio/virtio_pci.c
@@ -99,6 +99,9 @@ static void vp_finalize_features(struct virtio_device *vdev)
 {
         struct virtio_pci_device *vp_dev = to_vp_device(vdev);
 
+        /* Give virtio_ring a chance to accept features. */
+        vring_transport_features(vdev);
+
         /* We only support 32 feature bits. */
         BUILD_BUG_ON(ARRAY_SIZE(vdev->features) != 1);
         iowrite32(vdev->features[0], vp_dev->ioaddr+VIRTIO_PCI_GUEST_FEATURES);
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 21d9a62767af..6eb5303fed11 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -18,6 +18,7 @@
  */
 #include <linux/virtio.h>
 #include <linux/virtio_ring.h>
+#include <linux/virtio_config.h>
 #include <linux/device.h>
 
 #ifdef DEBUG
@@ -323,4 +324,19 @@ void vring_del_virtqueue(struct virtqueue *vq)
 }
 EXPORT_SYMBOL_GPL(vring_del_virtqueue);
 
+/* Manipulates transport-specific feature bits. */
+void vring_transport_features(struct virtio_device *vdev)
+{
+        unsigned int i;
+
+        for (i = VIRTIO_TRANSPORT_F_START; i < VIRTIO_TRANSPORT_F_END; i++) {
+                switch (i) {
+                default:
+                        /* We don't understand this bit. */
+                        clear_bit(i, vdev->features);
+                }
+        }
+}
+EXPORT_SYMBOL_GPL(vring_transport_features);
+
 MODULE_LICENSE("GPL");