[Qemu-devel] [PATCH 1/3] Fix geometry sector calculation

[Christian Borntraeger]

Currently the sector value for the geometry is masked based on
the sector size. This works fine for with 512 physical sector size,
but it fails for dasd devices on s390. A dasd device can have
a physical block size of 4096 (== same for logical block size)
and a typcial geometry of 15 heads and 12 sectors per cyl.
The ibm partition detection relies on a correct geometry
reported by the device. Unfortunately the current code changes
12 to 8. (This would be necessary for a physical block size /
device size that is not dividable by 4096) but for dasd this
is not the case.

This tries to fix the block layer by handling both cases
dasd and non-dasd by taking the physical block size into
account.

Signed-off-by: Christian Borntraeger <address@hidden>
CC: Christoph Hellwig <address@hidden>
---
 hw/virtio-blk.c |   12 +++++++++++-
 1 files changed, 11 insertions(+), 1 deletions(-)

diff --git a/hw/virtio-blk.c b/hw/virtio-blk.c
index 49990f8..5258533 100644
--- a/hw/virtio-blk.c
+++ b/hw/virtio-blk.c
@@ -483,6 +483,7 @@ static void virtio_blk_update_config(VirtIODevice *vdev, 
uint8_t *config)
     uint64_t capacity;
     int cylinders, heads, secs;
     int blk_size = s->conf->logical_block_size;
+    int pblk_size = s->conf->physical_block_size;
 
     bdrv_get_geometry(s->bs, &capacity);
     bdrv_get_geometry_hint(s->bs, &cylinders, &heads, &secs);
@@ -494,7 +495,16 @@ static void virtio_blk_update_config(VirtIODevice *vdev, 
uint8_t *config)
     stw_raw(&blkcfg.min_io_size, s->conf->min_io_size / blk_size);
     stw_raw(&blkcfg.opt_io_size, s->conf->opt_io_size / blk_size);
     blkcfg.heads = heads;
-    blkcfg.sectors = secs & ~s->sector_mask;
+    /*
+     * we must round down the block device size to a multiple of the logical
+     * block size. The geometry value for sectors is based on the physical
+     * sector size and NOT on the Linux default block size of 512. For
+     * example a dasd device usually has 12 sectors per track and each
+     * sector has 4096 bytes (the whole cylinder == 48k). The geometry
+     * is specified as secs=12. Thus we cannot use sector_mask, instead 
+     * we have to use some special case.
+     */
+    blkcfg.sectors = secs & ~(blk_size / pblk_size - 1);
     blkcfg.size_max = 0;
     blkcfg.physical_block_exp = get_physical_block_exp(s->conf);
     blkcfg.alignment_offset = 0;
-- 
1.7.0.1