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>

1 files changed, 74 insertions, 58 deletions

diff --git a/drivers/lguest/lguest_device.c b/drivers/lguest/lguest_device.c
index e2eec38c83c2..07f57a53658b 100644
--- a/drivers/lguest/lguest_device.c
+++ b/drivers/lguest/lguest_device.c
@@ -52,57 +52,82 @@ struct lguest_device {
 /*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)
 {
-        struct lguest_device_desc *desc = to_lgdev(vdev)->desc;
-        int i;
-
-        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;
-                }
-        }
+        return lg_features(desc) + desc->feature_len * 2;
+}
 
-        /* Not found: return NULL for failure. */
-        return NULL;
+/* 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;
+        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;
 }
 
 /* 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 @@ static void lg_notify(struct virtqueue *vq)
  *
  * 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 @@ static void lg_del_vq(struct virtqueue *vq)
 
 /* 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 @@ static void scan_devices(void)
         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);
         }
 }