virtio: meet virtio spec by finalizing features before using device

Virtio devices are supposed to negotiate features before they start using
the device, but the current code doesn't do this.  This is because the
driver's probe() function invariably has to add buffers to a virtqueue,
or probe the disk (virtio_blk).

This currently doesn't matter since no existing backend is strict about
the feature negotiation.  But it's possible to imagine a future feature
which completely changes how a device operates: in this case, we'd need
to acknowledge it before using the device.

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

1 files changed, 4 insertions, 3 deletions

diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index 018c070a357..6b681036486 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -118,13 +118,14 @@ static int virtio_dev_probe(struct device *_d)
                 if (device_features & (1 << i))
                         set_bit(i, dev->features);
 
+        dev->config->finalize_features(dev);
+
         err = drv->probe(dev);
         if (err)
                 add_status(dev, VIRTIO_CONFIG_S_FAILED);
-        else {
-                dev->config->finalize_features(dev);
+        else
                 add_status(dev, VIRTIO_CONFIG_S_DRIVER_OK);
-        }
+
         return err;
 }