[PATCH 1/2] virtio: allow drivers to validate features

["Michael S. Tsirkin" <mst@redhat.com>]

Some drivers can't support all features in all configurations.  At the
moment we blindly set FEATURES_OK and later FAILED.  Support this better
by adding a callback drivers can use to do some early checks.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 drivers/virtio/virtio.c | 6 ++++++
 include/linux/virtio.h  | 1 +
 2 files changed, 7 insertions(+)

diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index 400d70b..48230a5 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -232,6 +232,12 @@ static int virtio_dev_probe(struct device *_d)
 		if (device_features & (1ULL << i))
 			__virtio_set_bit(dev, i);
 
+	if (drv->validate) {
+		err = drv->validate(dev);
+		if (err)
+			goto err;
+	}
+
 	err = virtio_finalize_features(dev);
 	if (err)
 		goto err;
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index 193fea9..ed04753 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -176,6 +176,7 @@ struct virtio_driver {
 	unsigned int feature_table_size;
 	const unsigned int *feature_table_legacy;
 	unsigned int feature_table_size_legacy;
+	int (*validate)(struct virtio_device *dev);
 	int (*probe)(struct virtio_device *dev);
 	void (*scan)(struct virtio_device *dev);
 	void (*remove)(struct virtio_device *dev);
-- 
MST