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, 13 insertions, 9 deletions

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