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/block/virtio_blk.c b/drivers/block/virtio_blk.c
index cc6d393..78be6b8 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -242,7 +242,7 @@
index++;
/* If barriers are supported, tell block layer that queue is ordered */
- if (vdev->config->feature(vdev, VIRTIO_BLK_F_BARRIER))
+ if (virtio_has_feature(vdev, VIRTIO_BLK_F_BARRIER))
blk_queue_ordered(vblk->disk->queue, QUEUE_ORDERED_TAG, NULL);
/* Host must always specify the capacity. */
@@ -308,7 +308,13 @@
{ 0 },
};
+static unsigned int features[] = {
+ VIRTIO_BLK_F_BARRIER, VIRTIO_BLK_F_SEG_MAX, VIRTIO_BLK_F_SIZE_MAX,
+};
+
static struct virtio_driver virtio_blk = {
+ .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/lguest/lguest_device.c b/drivers/lguest/lguest_device.c
index 2bc9bf7..7a643a6 100644
--- a/drivers/lguest/lguest_device.c
+++ b/drivers/lguest/lguest_device.c
@@ -85,27 +85,34 @@
+ 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 *features;
+ u8 *in_features = lg_features(desc);
- /* 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;
+ /* 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);
- /* The feature bitmap comes after the virtqueues. */
- features = lg_features(desc);
- if (!(features[fbit / 8] & (1 << (fbit % 8))))
- return false;
+ return features;
+}
- /* 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;
+static void lg_set_features(struct virtio_device *vdev, u32 features)
+{
+ unsigned int i;
+ struct lguest_device_desc *desc = to_lgdev(vdev)->desc;
+ /* 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 @@
/* 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,
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index ad43421..f926b5a 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -378,26 +378,26 @@
SET_NETDEV_DEV(dev, &vdev->dev);
/* Do we support "hardware" checksums? */
- if (csum && vdev->config->feature(vdev, VIRTIO_NET_F_CSUM)) {
+ if (csum && virtio_has_feature(vdev, VIRTIO_NET_F_CSUM)) {
/* This opens up the world of extra features. */
dev->features |= NETIF_F_HW_CSUM|NETIF_F_SG|NETIF_F_FRAGLIST;
- if (gso && vdev->config->feature(vdev, VIRTIO_NET_F_GSO)) {
+ if (gso && virtio_has_feature(vdev, VIRTIO_NET_F_GSO)) {
dev->features |= NETIF_F_TSO | NETIF_F_UFO
| NETIF_F_TSO_ECN | NETIF_F_TSO6;
}
/* Individual feature bits: what can host handle? */
- if (gso && vdev->config->feature(vdev, VIRTIO_NET_F_HOST_TSO4))
+ if (gso && virtio_has_feature(vdev, VIRTIO_NET_F_HOST_TSO4))
dev->features |= NETIF_F_TSO;
- if (gso && vdev->config->feature(vdev, VIRTIO_NET_F_HOST_TSO6))
+ if (gso && virtio_has_feature(vdev, VIRTIO_NET_F_HOST_TSO6))
dev->features |= NETIF_F_TSO6;
- if (gso && vdev->config->feature(vdev, VIRTIO_NET_F_HOST_ECN))
+ if (gso && virtio_has_feature(vdev, VIRTIO_NET_F_HOST_ECN))
dev->features |= NETIF_F_TSO_ECN;
- if (gso && vdev->config->feature(vdev, VIRTIO_NET_F_HOST_UFO))
+ if (gso && virtio_has_feature(vdev, VIRTIO_NET_F_HOST_UFO))
dev->features |= NETIF_F_UFO;
}
/* Configuration may specify what MAC to use. Otherwise random. */
- if (vdev->config->feature(vdev, VIRTIO_NET_F_MAC)) {
+ if (virtio_has_feature(vdev, VIRTIO_NET_F_MAC)) {
vdev->config->get(vdev,
offsetof(struct virtio_net_config, mac),
dev->dev_addr, dev->addr_len);
@@ -486,7 +486,15 @@
{ 0 },
};
+static unsigned int features[] = {
+ VIRTIO_NET_F_CSUM, VIRTIO_NET_F_GSO, VIRTIO_NET_F_MAC,
+ VIRTIO_NET_F_HOST_TSO4, VIRTIO_NET_F_HOST_UFO, VIRTIO_NET_F_HOST_TSO6,
+ VIRTIO_NET_F_HOST_ECN,
+};
+
static struct virtio_driver virtio_net = {
+ .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.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 */
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index e7d1084..06005fa 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -76,6 +76,7 @@
* @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 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 @@
* 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 @@
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 475572e..50db245 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 @@
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 @@
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);