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virtio: explicit advertisement of driver features

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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>
This commit is contained in:
Rusty Russell
2008-05-02 21:50:50 -05:00
parent 72e61eb40b
commit c45a6816c1
8 changed files with 138 additions and 49 deletions
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38
drivers/virtio/virtio.c
View File

@@ -80,19 +80,51 @@ static void add_status(struct virtio_device *dev, unsigned status)
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 @@ static int virtio_dev_remove(struct device *_d)
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;