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>

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index dd7ea203f940dc664a9ac74ef9fa157ac3a36b5b..42251095134fa7746e8748150089c2dd570d21d8 100644 (file)
--- 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 6a66c7f30bcb52c0fa4f73a466f55d996818dd31..c1aef85243bf468522364425b6e06c022d9c8071 100644 (file)
--- 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. */