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>

2 files changed, 12 insertions, 1 deletions

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index dd7ea203f940..42251095134f 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -196,6 +196,7 @@ static int virtblk_probe(struct virtio_device *vdev)
         int err;
         u64 cap;
         u32 v;
+        u32 blk_size;
 
         if (index_to_minor(index) >= 1 << MINORBITS)
                 return -ENOSPC;
@@ -290,6 +291,13 @@ static int virtblk_probe(struct virtio_device *vdev)
         if (!err)
                 blk_queue_max_hw_segments(vblk->disk->queue, v);
 
+        /* Host can optionally specify the block size of the device */
+        err = virtio_config_val(vdev, VIRTIO_BLK_F_BLK_SIZE,
+                                offsetof(struct virtio_blk_config, blk_size),
+                                &blk_size);
+        if (!err)
+                blk_queue_hardsect_size(vblk->disk->queue, blk_size);
+
         add_disk(vblk->disk);
         return 0;
 
@@ -330,7 +338,7 @@ 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, VIRTIO_BLK_F_RO,
+        VIRTIO_BLK_F_GEOMETRY, VIRTIO_BLK_F_RO, VIRTIO_BLK_F_BLK_SIZE,
 };
 
 static struct virtio_driver virtio_blk = {
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. */