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>

4 files changed, 73 insertions, 67 deletions

diff --git a/include/linux/lguest_launcher.h b/include/linux/lguest_launcher.h
index 697104d..589be3e 100644
--- a/include/linux/lguest_launcher.h
+++ b/include/linux/lguest_launcher.h
@@ -23,7 +23,12 @@
 struct lguest_device_desc {
 	/* The device type: console, network, disk etc.  Type 0 terminates. */
 	__u8 type;
-	/* The number of bytes of the config array. */
+	/* The number of virtqueues (first in config array) */
+	__u8 num_vq;
+	/* The number of bytes of feature bits.  Multiply by 2: one for host
+	 * features and one for guest acknowledgements. */
+	__u8 feature_len;
+	/* The number of bytes of the config array after virtqueues. */
 	__u8 config_len;
 	/* A status byte, written by the Guest. */
 	__u8 status;
@@ -31,7 +36,7 @@ struct lguest_device_desc {
 };
 
 /*D:135 This is how we expect the device configuration field for a virtqueue
- * (type VIRTIO_CONFIG_F_VIRTQUEUE) to be laid out: */
+ * to be laid out in config space. */
 struct lguest_vqconfig {
 	/* The number of entries in the virtio_ring */
 	__u16 num;
diff --git a/include/linux/virtio_blk.h b/include/linux/virtio_blk.h
index 7bd2bce..e546356 100644
--- a/include/linux/virtio_blk.h
+++ b/include/linux/virtio_blk.h
@@ -6,15 +6,19 @@
 #define VIRTIO_ID_BLOCK	2
 
 /* Feature bits */
-#define VIRTIO_CONFIG_BLK_F	0x40
-#define VIRTIO_BLK_F_BARRIER	1	/* Does host support barriers? */
-
-/* The capacity (in 512-byte sectors). */
-#define VIRTIO_CONFIG_BLK_F_CAPACITY	0x41
-/* The maximum segment size. */
-#define VIRTIO_CONFIG_BLK_F_SIZE_MAX	0x42
-/* The maximum number of segments. */
-#define VIRTIO_CONFIG_BLK_F_SEG_MAX	0x43
+#define VIRTIO_BLK_F_BARRIER	0	/* Does host support barriers? */
+#define VIRTIO_BLK_F_SIZE_MAX	1	/* Indicates maximum segment size */
+#define VIRTIO_BLK_F_SEG_MAX	2	/* Indicates maximum # of segments */
+
+struct virtio_blk_config
+{
+	/* The capacity (in 512-byte sectors). */
+	__le64 capacity;
+	/* The maximum segment size (if VIRTIO_BLK_F_SIZE_MAX) */
+	__le32 size_max;
+	/* The maximum number of segments (if VIRTIO_BLK_F_SEG_MAX) */
+	__le32 seg_max;
+} __attribute__((packed));
 
 /* These two define direction. */
 #define VIRTIO_BLK_T_IN		0
diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index bcc0188..70bb260 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 */
diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
index ae469ae..6e8fdfe 100644
--- a/include/linux/virtio_net.h
+++ b/include/linux/virtio_net.h
@@ -5,16 +5,19 @@
 /* The ID for virtio_net */
 #define VIRTIO_ID_NET	1
 
-/* The bitmap of config for virtio net */
-#define VIRTIO_CONFIG_NET_F	0x40
+/* The feature bitmap for virtio net */
 #define VIRTIO_NET_F_NO_CSUM	0
 #define VIRTIO_NET_F_TSO4	1
 #define VIRTIO_NET_F_UFO	2
 #define VIRTIO_NET_F_TSO4_ECN	3
 #define VIRTIO_NET_F_TSO6	4
+#define VIRTIO_NET_F_MAC	5
 
-/* The config defining mac address. */
-#define VIRTIO_CONFIG_NET_MAC_F	0x41
+struct virtio_net_config
+{
+	/* The config defining mac address (if VIRTIO_NET_F_MAC) */
+	__u8 mac[6];
+} __attribute__((packed));
 
 /* This is the first element of the scatter-gather list.  If you don't
  * specify GSO or CSUM features, you can simply ignore the header. */