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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 /drivers/lguest
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 'drivers/lguest')
-rw-r--r--drivers/lguest/lguest_device.c48
1 files changed, 28 insertions, 20 deletions
diff --git a/drivers/lguest/lguest_device.c b/drivers/lguest/lguest_device.c
index 2bc9bf7e88e..7a643a6ee9a 100644
--- a/drivers/lguest/lguest_device.c
+++ b/drivers/lguest/lguest_device.c
@@ -85,27 +85,34 @@ static unsigned desc_size(const struct lguest_device_desc *desc)
+ desc->config_len;
}
-/* This tests (and acknowleges) a feature bit. */
-static bool lg_feature(struct virtio_device *vdev, unsigned fbit)
+/* This gets the device's feature bits. */
+static u32 lg_get_features(struct virtio_device *vdev)
{
+ unsigned int i;
+ u32 features = 0;
+ struct lguest_device_desc *desc = to_lgdev(vdev)->desc;
+ u8 *in_features = lg_features(desc);
+
+ /* We do this the slow but generic way. */
+ for (i = 0; i < min(desc->feature_len * 8, 32); i++)
+ if (in_features[i / 8] & (1 << (i % 8)))
+ features |= (1 << i);
+
+ return features;
+}
+
+static void lg_set_features(struct virtio_device *vdev, u32 features)
+{
+ unsigned int i;
struct lguest_device_desc *desc = to_lgdev(vdev)->desc;
- u8 *features;
-
- /* Obviously if they ask for a feature off the end of our feature
- * bitmap, it's not set. */
- if (fbit / 8 > desc->feature_len)
- return false;
-
- /* The feature bitmap comes after the virtqueues. */
- features = lg_features(desc);
- if (!(features[fbit / 8] & (1 << (fbit % 8))))
- return false;
-
- /* We set the matching bit in the other half of the bitmap to tell the
- * Host we want to use this feature. We don't use this yet, but we
- * could in future. */
- features[desc->feature_len + fbit / 8] |= (1 << (fbit % 8));
- return true;
+ /* Second half of bitmap is features we accept. */
+ u8 *out_features = lg_features(desc) + desc->feature_len;
+
+ memset(out_features, 0, desc->feature_len);
+ for (i = 0; i < min(desc->feature_len * 8, 32); i++) {
+ if (features & (1 << i))
+ out_features[i / 8] |= (1 << (i % 8));
+ }
}
/* Once they've found a field, getting a copy of it is easy. */
@@ -286,7 +293,8 @@ static void lg_del_vq(struct virtqueue *vq)
/* The ops structure which hooks everything together. */
static struct virtio_config_ops lguest_config_ops = {
- .feature = lg_feature,
+ .get_features = lg_get_features,
+ .set_features = lg_set_features,
.get = lg_get,
.set = lg_set,
.get_status = lg_get_status,