[PATCH] migration/block-dirty-bitmap: fix larger granularity bitmaps

[Stefan Reiter <s.reiter@proxmox.com>]

sectors_per_chunk is a 64 bit integer, but the calculation is done in 32
bits, leading to an overflow for coarse bitmap granularities.

If that results in the value 0, it leads to a hang where no progress is
made but send_bitmap_bits is constantly called with nr_sectors being 0.

Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>
---
 migration/block-dirty-bitmap.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/migration/block-dirty-bitmap.c b/migration/block-dirty-bitmap.c
index 5bef793ac0..5398869e2b 100644
--- a/migration/block-dirty-bitmap.c
+++ b/migration/block-dirty-bitmap.c
@@ -562,8 +562,9 @@ static int add_bitmaps_to_list(DBMSaveState *s, BlockDriverState *bs,
         dbms->bitmap_alias = g_strdup(bitmap_alias);
         dbms->bitmap = bitmap;
         dbms->total_sectors = bdrv_nb_sectors(bs);
-        dbms->sectors_per_chunk = CHUNK_SIZE * 8 *
+        dbms->sectors_per_chunk = CHUNK_SIZE * 8lu *
             bdrv_dirty_bitmap_granularity(bitmap) >> BDRV_SECTOR_BITS;
+        assert(dbms->sectors_per_chunk != 0);
         if (bdrv_dirty_bitmap_enabled(bitmap)) {
             dbms->flags |= DIRTY_BITMAP_MIG_START_FLAG_ENABLED;
         }
-- 
2.20.1