virtio: add virtio disk geometry feature

Rather than faking up some geometry, allow the backend to push the disk
geometry via virtio pci config option.  Keep the old geo code around for
compatibility.
Signed-off-by: Ryan Harper <ryanh@us.ibm.com>
Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> (modified to single struct)

drivers/block/virtio_blk.c

@@ -157,10 +157,25 @@ static int virtblk_ioctl(struct inode *inode, struct file *filp,
 /* We provide getgeo only to please some old bootloader/partitioning tools */
 static int virtblk_getgeo(struct block_device *bd, struct hd_geometry *geo)
 {
+	struct virtio_blk *vblk = bd->bd_disk->private_data;
+	struct virtio_blk_geometry vgeo;
+	int err;
+
+	/* see if the host passed in geometry config */
+	err = virtio_config_val(vblk->vdev, VIRTIO_BLK_F_GEOMETRY,
+				offsetof(struct virtio_blk_config, geometry),
+				&vgeo);
+
+	if (!err) {
+		geo->heads = vgeo.heads;
+		geo->sectors = vgeo.sectors;
+		geo->cylinders = vgeo.cylinders;
+	} else {
 		/* some standard values, similar to sd */
 		geo->heads = 1 << 6;
 		geo->sectors = 1 << 5;
 		geo->cylinders = get_capacity(bd->bd_disk) >> 11;
+	}
 	return 0;
 }
 
@@ -310,6 +325,7 @@ static struct virtio_device_id id_table[] = {
 
 static unsigned int features[] = {
 	VIRTIO_BLK_F_BARRIER, VIRTIO_BLK_F_SEG_MAX, VIRTIO_BLK_F_SIZE_MAX,
+	VIRTIO_BLK_F_GEOMETRY,
 };
 
 static struct virtio_driver virtio_blk = {

include/linux/virtio_blk.h

@@ -9,6 +9,7 @@
 #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 */
+#define VIRTIO_BLK_F_GEOMETRY	4	/* Legacy geometry available  */
 
 struct virtio_blk_config
 {
@@ -18,6 +19,12 @@ struct virtio_blk_config
 	__le32 size_max;
 	/* The maximum number of segments (if VIRTIO_BLK_F_SEG_MAX) */
 	__le32 seg_max;
+	/* geometry the device (if VIRTIO_BLK_F_GEOMETRY) */
+	struct virtio_blk_geometry {
+		__le16 cylinders;
+		__u8 heads;
+		__u8 sectors;
+	} geometry;
 } __attribute__((packed));
 
 /* These two define direction. */