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authorRusty Russell <rusty@rustcorp.com.au>2008-05-02 21:50:50 -0500
committerRusty Russell <rusty@rustcorp.com.au>2008-05-02 21:50:50 +1000
commitc45a6816c19dee67b8f725e6646d428901a6dc24 (patch)
tree096e3263fd14e140685bcc3082394ff15f5aeddb /include/linux
parent72e61eb40b55dd57031ec5971e810649f82b0259 (diff)
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>
Diffstat (limited to 'include/linux')
-rw-r--r--include/linux/virtio.h7
-rw-r--r--include/linux/virtio_config.h36
2 files changed, 36 insertions, 7 deletions
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index e7d10845b3c1..06005fa9e982 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -76,6 +76,7 @@ struct virtqueue_ops {
* @dev: underlying device.
* @id: the device type identification (used to match it with a driver).
* @config: the configuration ops for this device.
+ * @features: the features supported by both driver and device.
* @priv: private pointer for the driver's use.
*/
struct virtio_device
@@ -84,6 +85,8 @@ struct virtio_device
struct device dev;
struct virtio_device_id id;
struct virtio_config_ops *config;
+ /* Note that this is a Linux set_bit-style bitmap. */
+ unsigned long features[1];
void *priv;
};
@@ -94,6 +97,8 @@ void unregister_virtio_device(struct virtio_device *dev);
* virtio_driver - operations for a virtio I/O driver
* @driver: underlying device driver (populate name and owner).
* @id_table: the ids serviced by this driver.
+ * @feature_table: an array of feature numbers supported by this device.
+ * @feature_table_size: number of entries in the feature table array.
* @probe: the function to call when a device is found. Returns a token for
* remove, or PTR_ERR().
* @remove: the function when a device is removed.
@@ -103,6 +108,8 @@ void unregister_virtio_device(struct virtio_device *dev);
struct virtio_driver {
struct device_driver driver;
const struct virtio_device_id *id_table;
+ const unsigned int *feature_table;
+ unsigned int feature_table_size;
int (*probe)(struct virtio_device *dev);
void (*remove)(struct virtio_device *dev);
void (*config_changed)(struct virtio_device *dev);
diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index 475572e976fe..50db245c81ad 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -20,11 +20,6 @@
/**
* virtio_config_ops - operations for configuring a virtio device
- * @feature: search for a feature in this config
- * vdev: the virtio_device
- * bit: the feature bit
- * Returns true if the feature is supported. Acknowledges the feature
- * so the host can see it.
* @get: read the value of a configuration field
* vdev: the virtio_device
* offset: the offset of the configuration field
@@ -50,10 +45,15 @@
* callback: the virqtueue callback
* Returns the new virtqueue or ERR_PTR() (eg. -ENOENT).
* @del_vq: free a virtqueue found by find_vq().
+ * @get_features: get the array of feature bits for this device.
+ * vdev: the virtio_device
+ * Returns the first 32 feature bits (all we currently need).
+ * @set_features: confirm what device features we'll be using.
+ * vdev: the virtio_device
+ * feature: the first 32 feature bits
*/
struct virtio_config_ops
{
- bool (*feature)(struct virtio_device *vdev, unsigned bit);
void (*get)(struct virtio_device *vdev, unsigned offset,
void *buf, unsigned len);
void (*set)(struct virtio_device *vdev, unsigned offset,
@@ -65,8 +65,30 @@ struct virtio_config_ops
unsigned index,
void (*callback)(struct virtqueue *));
void (*del_vq)(struct virtqueue *vq);
+ u32 (*get_features)(struct virtio_device *vdev);
+ void (*set_features)(struct virtio_device *vdev, u32 features);
};
+/* If driver didn't advertise the feature, it will never appear. */
+void virtio_check_driver_offered_feature(const struct virtio_device *vdev,
+ unsigned int fbit);
+
+/**
+ * virtio_has_feature - helper to determine if this device has this feature.
+ * @vdev: the device
+ * @fbit: the feature bit
+ */
+static inline bool virtio_has_feature(const struct virtio_device *vdev,
+ unsigned int fbit)
+{
+ /* Did you forget to fix assumptions on max features? */
+ if (__builtin_constant_p(fbit))
+ BUILD_BUG_ON(fbit >= 32);
+
+ virtio_check_driver_offered_feature(vdev, fbit);
+ return test_bit(fbit, vdev->features);
+}
+
/**
* virtio_config_val - look for a feature and get a virtio config entry.
* @vdev: the virtio device
@@ -84,7 +106,7 @@ static inline int virtio_config_buf(struct virtio_device *vdev,
unsigned int offset,
void *buf, unsigned len)
{
- if (!vdev->config->feature(vdev, fbit))
+ if (!virtio_has_feature(vdev, fbit))
return -ENOENT;
vdev->config->get(vdev, offset, buf, len);