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, 46 insertions, 52 deletions

diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index bcc01888df78..70bb26062d76 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -5,7 +5,7 @@
  * store and access that space differently. */
 #include <linux/types.h>
 
-/* Status byte for guest to report progress, and synchronize config. */
+/* Status byte for guest to report progress, and synchronize features. */
 /* We have seen device and processed generic fields (VIRTIO_CONFIG_F_VIRTIO) */
 #define VIRTIO_CONFIG_S_ACKNOWLEDGE     1
 /* We have found a driver for the device. */
@@ -15,34 +15,27 @@
 /* We've given up on this device. */
 #define VIRTIO_CONFIG_S_FAILED          0x80
 
-/* Feature byte (actually 7 bits availabe): */
-/* Requirements/features of the virtio implementation. */
-#define VIRTIO_CONFIG_F_VIRTIO 1
-/* Requirements/features of the virtqueue (may have more than one). */
-#define VIRTIO_CONFIG_F_VIRTQUEUE 2
-
 #ifdef __KERNEL__
 struct virtio_device;
 
 /**
  * virtio_config_ops - operations for configuring a virtio device
- * @find: search for the next configuration field of the given type.
+ * @feature: search for a feature in this config
  *      vdev: the virtio_device
- *      type: the feature type
- *      len: the (returned) length of the field if found.
- *      Returns a token if found, or NULL.  Never returnes the same field twice
- *      (ie. it's used up).
- * @get: read the value of a configuration field after find().
+ *      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
- *      token: the token returned from find().
+ *      offset: the offset of the configuration field
  *      buf: the buffer to write the field value into.
- *      len: the length of the buffer (given by find()).
+ *      len: the length of the buffer
  *      Note that contents are conventionally little-endian.
- * @set: write the value of a configuration field after find().
+ * @set: write the value of a configuration field
  *      vdev: the virtio_device
- *      token: the token returned from find().
+ *      offset: the offset of the configuration field
  *      buf: the buffer to read the field value from.
- *      len: the length of the buffer (given by find()).
+ *      len: the length of the buffer
  *      Note that contents are conventionally little-endian.
  * @get_status: read the status byte
  *      vdev: the virtio_device
@@ -50,62 +43,63 @@ struct virtio_device;
  * @set_status: write the status byte
  *      vdev: the virtio_device
  *      status: the new status byte
- * @find_vq: find the first VIRTIO_CONFIG_F_VIRTQUEUE and create a virtqueue.
+ * @find_vq: find a virtqueue and instantiate it.
  *      vdev: the virtio_device
+ *      index: the 0-based virtqueue number in case there's more than one.
  *      callback: the virqtueue callback
- *      Returns the new virtqueue or ERR_PTR().
+ *      Returns the new virtqueue or ERR_PTR() (eg. -ENOENT).
  * @del_vq: free a virtqueue found by find_vq().
  */
 struct virtio_config_ops
 {
-        void *(*find)(struct virtio_device *vdev, u8 type, unsigned *len);
-        void (*get)(struct virtio_device *vdev, void *token,
+        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, void *token,
+        void (*set)(struct virtio_device *vdev, unsigned offset,
                     const void *buf, unsigned len);
         u8 (*get_status)(struct virtio_device *vdev);
         void (*set_status)(struct virtio_device *vdev, u8 status);
         struct virtqueue *(*find_vq)(struct virtio_device *vdev,
+                                     unsigned index,
                                      bool (*callback)(struct virtqueue *));
         void (*del_vq)(struct virtqueue *vq);
 };
 
 /**
- * virtio_config_val - get a single virtio config and mark it used.
- * @config: the virtio config space
- * @type: the type to search for.
+ * virtio_config_val - look for a feature and get a single virtio config.
+ * @vdev: the virtio device
+ * @fbit: the feature bit
+ * @offset: the type to search for.
  * @val: a pointer to the value to fill in.
  *
- * Once used, the config type is marked with VIRTIO_CONFIG_F_USED so it can't
- * be found again.  This version does endian conversion. */
-#define virtio_config_val(vdev, type, v) ({                             \
-        int _err = __virtio_config_val((vdev),(type),(v),sizeof(*(v))); \
-                                                                        \
-        BUILD_BUG_ON(sizeof(*(v)) != 1 && sizeof(*(v)) != 2             \
-                     && sizeof(*(v)) != 4 && sizeof(*(v)) != 8);        \
-        if (!_err) {                                                    \
-                switch (sizeof(*(v))) {                                 \
-                case 2: le16_to_cpus((__u16 *) v); break;               \
-                case 4: le32_to_cpus((__u32 *) v); break;               \
-                case 8: le64_to_cpus((__u64 *) v); break;               \
-                }                                                       \
-        }                                                               \
+ * The return value is -ENOENT if the feature doesn't exist.  Otherwise
+ * the value is endian-corrected and returned in v. */
+#define virtio_config_val(vdev, fbit, offset, v) ({                     \
+        int _err;                                                       \
+        if ((vdev)->config->feature((vdev), (fbit))) {                  \
+                __virtio_config_val((vdev), (offset), (v));             \
+                _err = 0;                                               \
+        } else                                                          \
+                _err = -ENOENT;                                         \
         _err;                                                           \
 })
 
-int __virtio_config_val(struct virtio_device *dev,
-                        u8 type, void *val, size_t size);
-
 /**
- * virtio_use_bit - helper to use a feature bit in a bitfield value.
- * @dev: the virtio device
- * @token: the token as returned from vdev->config->find().
- * @len: the length of the field.
- * @bitnum: the bit to test.
+ * __virtio_config_val - get a single virtio config without feature check.
+ * @vdev: the virtio device
+ * @offset: the type to search for.
+ * @val: a pointer to the value to fill in.
  *
- * If handed a NULL token, it returns false, otherwise returns bit status.
- * If it's one, it sets the mirroring acknowledgement bit. */
-int virtio_use_bit(struct virtio_device *vdev,
-                   void *token, unsigned int len, unsigned int bitnum);
+ * The value is endian-corrected and returned in v. */
+#define __virtio_config_val(vdev, offset, v) do {                       \
+        BUILD_BUG_ON(sizeof(*(v)) != 1 && sizeof(*(v)) != 2             \
+                     && sizeof(*(v)) != 4 && sizeof(*(v)) != 8);        \
+        (vdev)->config->get((vdev), (offset), (v), sizeof(*(v)));       \
+        switch (sizeof(*(v))) {                                         \
+        case 2: le16_to_cpus((__u16 *) v); break;                       \
+        case 4: le32_to_cpus((__u32 *) v); break;                       \
+        case 8: le64_to_cpus((__u64 *) v); break;                       \
+        }                                                               \
+} while(0)
 #endif /* __KERNEL__ */
 #endif /* _LINUX_VIRTIO_CONFIG_H */