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;
diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index fef88d8..bfef604 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -227,7 +227,7 @@
}
vb->tell_host_first
- = vdev->config->feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
+ = virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
return 0;
@@ -259,7 +259,11 @@
kfree(vb);
}
+static unsigned int features[] = { VIRTIO_BALLOON_F_MUST_TELL_HOST };
+
static struct virtio_driver virtio_balloon = {
+ .feature_table = features,
+ .feature_table_size = ARRAY_SIZE(features),
.driver.name = KBUILD_MODNAME,
.driver.owner = THIS_MODULE,
.id_table = id_table,
diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c
index de102a6..27e9fc9 100644
--- a/drivers/virtio/virtio_pci.c
+++ b/drivers/virtio/virtio_pci.c
@@ -87,23 +87,22 @@
return container_of(vdev, struct virtio_pci_device, vdev);
}
-/* virtio config->feature() implementation */
-static bool vp_feature(struct virtio_device *vdev, unsigned bit)
+/* virtio config->get_features() implementation */
+static u32 vp_get_features(struct virtio_device *vdev)
{
struct virtio_pci_device *vp_dev = to_vp_device(vdev);
- u32 mask;
- /* Since this function is supposed to have the side effect of
- * enabling a queried feature, we simulate that by doing a read
- * from the host feature bitmask and then writing to the guest
- * feature bitmask */
- mask = ioread32(vp_dev->ioaddr + VIRTIO_PCI_HOST_FEATURES);
- if (mask & (1 << bit)) {
- mask |= (1 << bit);
- iowrite32(mask, vp_dev->ioaddr + VIRTIO_PCI_GUEST_FEATURES);
- }
+ /* When someone needs more than 32 feature bits, we'll need to
+ * steal a bit to indicate that the rest are somewhere else. */
+ return ioread32(vp_dev->ioaddr + VIRTIO_PCI_HOST_FEATURES);
+}
- return !!(mask & (1 << bit));
+/* virtio config->set_features() implementation */
+static void vp_set_features(struct virtio_device *vdev, u32 features)
+{
+ struct virtio_pci_device *vp_dev = to_vp_device(vdev);
+
+ iowrite32(features, vp_dev->ioaddr + VIRTIO_PCI_GUEST_FEATURES);
}
/* virtio config->get() implementation */
@@ -293,7 +292,6 @@
}
static struct virtio_config_ops virtio_pci_config_ops = {
- .feature = vp_feature,
.get = vp_get,
.set = vp_set,
.get_status = vp_get_status,
@@ -301,6 +299,8 @@
.reset = vp_reset,
.find_vq = vp_find_vq,
.del_vq = vp_del_vq,
+ .get_features = vp_get_features,
+ .set_features = vp_set_features,
};
/* the PCI probing function */