virtio: explicit advertisement of driver features
A recent proposed feature addition to the virtio block driver revealed
some flaws in the API: in particular, we assume that feature
negotiation is complete once a driver's probe function returns.
There is nothing in the API to require this, however, and even I
didn't notice when it was violated.
So instead, we require the driver to specify what features it supports
in a table, we can then move the feature negotiation into the virtio
core. The intersection of device and driver features are presented in
a new 'features' bitmap in the struct virtio_device.
Note that this highlights the difference between Linux unsigned-long
bitmaps where each unsigned long is in native endian, and a
straight-forward little-endian array of bytes.
Drivers can still remove feature bits in their probe routine if they
really have to.
API changes:
- dev->config->feature() no longer gets and acks a feature.
- drivers should advertise their features in the 'feature_table' field
- use virtio_has_feature() for extra sanity when checking feature bits
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index b535483..1386678 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -80,19 +80,51 @@
dev->config->set_status(dev, dev->config->get_status(dev) | status);
}
+void virtio_check_driver_offered_feature(const struct virtio_device *vdev,
+ unsigned int fbit)
+{
+ unsigned int i;
+ struct virtio_driver *drv = container_of(vdev->dev.driver,
+ struct virtio_driver, driver);
+
+ for (i = 0; i < drv->feature_table_size; i++)
+ if (drv->feature_table[i] == fbit)
+ return;
+ BUG();
+}
+EXPORT_SYMBOL_GPL(virtio_check_driver_offered_feature);
+
static int virtio_dev_probe(struct device *_d)
{
- int err;
+ int err, i;
struct virtio_device *dev = container_of(_d,struct virtio_device,dev);
struct virtio_driver *drv = container_of(dev->dev.driver,
struct virtio_driver, driver);
+ u32 device_features;
+ /* We have a driver! */
add_status(dev, VIRTIO_CONFIG_S_DRIVER);
+
+ /* Figure out what features the device supports. */
+ device_features = dev->config->get_features(dev);
+
+ /* Features supported by both device and driver into dev->features. */
+ memset(dev->features, 0, sizeof(dev->features));
+ for (i = 0; i < drv->feature_table_size; i++) {
+ unsigned int f = drv->feature_table[i];
+ BUG_ON(f >= 32);
+ if (device_features & (1 << f))
+ set_bit(f, dev->features);
+ }
+
err = drv->probe(dev);
if (err)
add_status(dev, VIRTIO_CONFIG_S_FAILED);
- else
+ else {
add_status(dev, VIRTIO_CONFIG_S_DRIVER_OK);
+ /* They should never have set feature bits beyond 32 */
+ dev->config->set_features(dev, dev->features[0]);
+ }
return err;
}
@@ -114,6 +146,8 @@
int register_virtio_driver(struct virtio_driver *driver)
{
+ /* Catch this early. */
+ BUG_ON(driver->feature_table_size && !driver->feature_table);
driver->driver.bus = &virtio_bus;
driver->driver.probe = virtio_dev_probe;
driver->driver.remove = virtio_dev_remove;