lk/linux-kernel-test
1
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity

virtio: explicit advertisement of driver features

Browse Source 
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
Download Patch File Download Diff File Expand all files Collapse all files

36
include/linux/virtio_config.h
View File

@ -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);