virtio-blk: Fix geometry sector calculation

Currently the sector value for the geometry is masked, even if the
user usesa command line parameter that explicitely gives a number.
This breaks 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 if the total size is
not a multiple of logical sector size,  but for dasd this
is not the case.

This patch checks the device size and only applies sector
mask if necessary.
Signed-off-by: NChristian Borntraeger <borntraeger@de.ibm.com>
CC: Christoph Hellwig <hch@lst.de>
Reviewed-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
(cherry picked from commit 136be99e)
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>

hw/virtio-blk.c

@@ -489,7 +489,22 @@ 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;
+    /*
+     * We must ensure that the block device capacity is a multiple of
+     * the logical block size. If that is not the case, lets use
+     * sector_mask to adopt the geometry to have a correct picture.
+     * For those devices where the capacity is ok for the given geometry
+     * we dont touch the sector value of the geometry, since some devices
+     * (like s390 dasd) need a specific value. Here the capacity is already
+     * cyls*heads*secs*blk_size and the sector value is not block size
+     * divided by 512 - instead it is the amount of blk_size blocks
+     * per track (cylinder).
+     */
+    if (bdrv_getlength(s->bs) /  heads / secs % blk_size) {
         blkcfg.sectors = secs & ~s->sector_mask;
+    } else {
+        blkcfg.sectors = secs;
+    }
     blkcfg.size_max = 0;
     blkcfg.physical_block_exp = get_physical_block_exp(s->conf);
     blkcfg.alignment_offset = 0;