virtio: simplify config mechanism.
Previously we used a type/len pair within the config space, but this
seems overkill. We now simply define a structure which represents the
layout in the config space: the config space can now only be extended
at the end.
The main driver-visible changes:
1) We indicate what fields are present with an explicit feature bit.
2) Virtqueues are explicitly numbered, and not in the config space.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/drivers/lguest/lguest_device.c b/drivers/lguest/lguest_device.c
index e2eec38..07f57a5 100644
--- a/drivers/lguest/lguest_device.c
+++ b/drivers/lguest/lguest_device.c
@@ -52,57 +52,82 @@
/*D:130
* Device configurations
*
- * The configuration information for a device consists of a series of fields.
- * We don't really care what they are: the Launcher set them up, and the driver
- * will look at them during setup.
+ * The configuration information for a device consists of one or more
+ * virtqueues, a feature bitmaks, and some configuration bytes. The
+ * configuration bytes don't really matter to us: the Launcher set them up, and
+ * the driver will look at them during setup.
*
- * For us these fields come immediately after that device's descriptor in the
- * lguest_devices page.
- *
- * Each field starts with a "type" byte, a "length" byte, then that number of
- * bytes of configuration information. The device descriptor tells us the
- * total configuration length so we know when we've reached the last field. */
+ * A convenient routine to return the device's virtqueue config array:
+ * immediately after the descriptor. */
+static struct lguest_vqconfig *lg_vq(const struct lguest_device_desc *desc)
+{
+ return (void *)(desc + 1);
+}
-/* type + length bytes */
-#define FHDR_LEN 2
+/* The features come immediately after the virtqueues. */
+static u8 *lg_features(const struct lguest_device_desc *desc)
+{
+ return (void *)(lg_vq(desc) + desc->num_vq);
+}
-/* This finds the first field of a given type for a device's configuration. */
-static void *lg_find(struct virtio_device *vdev, u8 type, unsigned int *len)
+/* The config space comes after the two feature bitmasks. */
+static u8 *lg_config(const struct lguest_device_desc *desc)
+{
+ return lg_features(desc) + desc->feature_len * 2;
+}
+
+/* The total size of the config page used by this device (incl. desc) */
+static unsigned desc_size(const struct lguest_device_desc *desc)
+{
+ return sizeof(*desc)
+ + desc->num_vq * sizeof(struct lguest_vqconfig)
+ + desc->feature_len * 2
+ + desc->config_len;
+}
+
+/* This tests (and acknowleges) a feature bit. */
+static bool lg_feature(struct virtio_device *vdev, unsigned fbit)
{
struct lguest_device_desc *desc = to_lgdev(vdev)->desc;
- int i;
+ u8 *features;
- for (i = 0; i < desc->config_len; i += FHDR_LEN + desc->config[i+1]) {
- if (desc->config[i] == type) {
- /* Mark it used, so Host can know we looked at it, and
- * also so we won't find the same one twice. */
- desc->config[i] |= 0x80;
- /* Remember, the second byte is the length. */
- *len = desc->config[i+1];
- /* We return a pointer to the field header. */
- return desc->config + i;
- }
- }
+ /* 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;
- /* Not found: return NULL for failure. */
- return NULL;
+ /* 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;
}
/* Once they've found a field, getting a copy of it is easy. */
-static void lg_get(struct virtio_device *vdev, void *token,
+static void lg_get(struct virtio_device *vdev, unsigned int offset,
void *buf, unsigned len)
{
- /* Check they didn't ask for more than the length of the field! */
- BUG_ON(len > ((u8 *)token)[1]);
- memcpy(buf, token + FHDR_LEN, len);
+ struct lguest_device_desc *desc = to_lgdev(vdev)->desc;
+
+ /* Check they didn't ask for more than the length of the config! */
+ BUG_ON(offset + len > desc->config_len);
+ memcpy(buf, lg_config(desc) + offset, len);
}
/* Setting the contents is also trivial. */
-static void lg_set(struct virtio_device *vdev, void *token,
+static void lg_set(struct virtio_device *vdev, unsigned int offset,
const void *buf, unsigned len)
{
- BUG_ON(len > ((u8 *)token)[1]);
- memcpy(token + FHDR_LEN, buf, len);
+ struct lguest_device_desc *desc = to_lgdev(vdev)->desc;
+
+ /* Check they didn't ask for more than the length of the config! */
+ BUG_ON(offset + len > desc->config_len);
+ memcpy(lg_config(desc) + offset, buf, len);
}
/* The operations to get and set the status word just access the status field
@@ -165,39 +190,29 @@
*
* So we provide devices with a "find virtqueue and set it up" function. */
static struct virtqueue *lg_find_vq(struct virtio_device *vdev,
+ unsigned index,
bool (*callback)(struct virtqueue *vq))
{
+ struct lguest_device *ldev = to_lgdev(vdev);
struct lguest_vq_info *lvq;
struct virtqueue *vq;
- unsigned int len;
- void *token;
int err;
- /* Look for a field of the correct type to mark a virtqueue. Note that
- * if this succeeds, then the type will be changed so it won't be found
- * again, and future lg_find_vq() calls will find the next
- * virtqueue (if any). */
- token = vdev->config->find(vdev, VIRTIO_CONFIG_F_VIRTQUEUE, &len);
- if (!token)
+ /* We must have this many virtqueues. */
+ if (index >= ldev->desc->num_vq)
return ERR_PTR(-ENOENT);
lvq = kmalloc(sizeof(*lvq), GFP_KERNEL);
if (!lvq)
return ERR_PTR(-ENOMEM);
- /* Note: we could use a configuration space inside here, just like we
- * do for the device. This would allow expansion in future, because
- * our configuration system is designed to be expansible. But this is
- * way easier. */
- if (len != sizeof(lvq->config)) {
- dev_err(&vdev->dev, "Unexpected virtio config len %u\n", len);
- err = -EIO;
- goto free_lvq;
- }
- /* Make a copy of the "struct lguest_vqconfig" field. We need a copy
- * because the config space might not be aligned correctly. */
- vdev->config->get(vdev, token, &lvq->config, sizeof(lvq->config));
+ /* Make a copy of the "struct lguest_vqconfig" entry, which sits after
+ * the descriptor. We need a copy because the config space might not
+ * be aligned correctly. */
+ memcpy(&lvq->config, lg_vq(ldev->desc)+index, sizeof(lvq->config));
+ printk("Mapping virtqueue %i addr %lx\n", index,
+ (unsigned long)lvq->config.pfn << PAGE_SHIFT);
/* Figure out how many pages the ring will take, and map that memory */
lvq->pages = lguest_map((unsigned long)lvq->config.pfn << PAGE_SHIFT,
DIV_ROUND_UP(vring_size(lvq->config.num,
@@ -259,7 +274,7 @@
/* The ops structure which hooks everything together. */
static struct virtio_config_ops lguest_config_ops = {
- .find = lg_find,
+ .feature = lg_feature,
.get = lg_get,
.set = lg_set,
.get_status = lg_get_status,
@@ -329,13 +344,14 @@
struct lguest_device_desc *d;
/* We start at the page beginning, and skip over each entry. */
- for (i = 0; i < PAGE_SIZE; i += sizeof(*d) + d->config_len) {
+ for (i = 0; i < PAGE_SIZE; i += desc_size(d)) {
d = lguest_devices + i;
/* Once we hit a zero, stop. */
if (d->type == 0)
break;
+ printk("Device at %i has size %u\n", i, desc_size(d));
add_lguest_device(d);
}
}