virtio_blk: check for hardsector size from host

Currently virtio_blk assumes a 512 byte hard sector size. This can cause
trouble / performance issues if the backing has a different block size
(like a file on an ext3 file system formatted with 4k block size or a dasd).

Lets add a feature flag that tells the guest to use a different hard sector
size than 512 byte.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/linux/virtio_blk.h b/include/linux/virtio_blk.h
index 6a66c7f30bcb..c1aef85243bf 100644
--- a/include/linux/virtio_blk.h
+++ b/include/linux/virtio_blk.h
@@ -13,6 +13,7 @@
 #define VIRTIO_BLK_F_SEG_MAX    2       /* Indicates maximum # of segments */
 #define VIRTIO_BLK_F_GEOMETRY   4       /* Legacy geometry available  */
 #define VIRTIO_BLK_F_RO         5       /* Disk is read-only */
+#define VIRTIO_BLK_F_BLK_SIZE   6       /* Block size of disk is available*/
 
 struct virtio_blk_config
 {
@@ -28,6 +29,8 @@ struct virtio_blk_config
                 __u8 heads;
                 __u8 sectors;
         } geometry;
+        /* block size of device (if VIRTIO_BLK_F_BLK_SIZE) */
+        __u32 blk_size;
 } __attribute__((packed));
 
 /* These two define direction. */