In parallels_check_duplicate() We use a bitmap for duplication detection.
This bitmap is not related to used_bmap field in BDRVParallelsState. Add
a comment about it to avoid confusion.

Signed-off-by: Alexander Ivanov <alexander.ivanov@virtuozzo.com>
---
 block/parallels.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/block/parallels.c b/block/parallels.c
index dad2bf67cf..dd8ec925f3 100644
--- a/block/parallels.c
+++ b/block/parallels.c
@@ -837,7 +837,10 @@ parallels_check_duplicate(BlockDriverState *bs, BdrvCheckResult *res,
     bool fixed = false;
 
     /*
-     * Create a bitmap of used clusters.
+     * Create a bitmap of used clusters. Please note that this bitmap is not
+     * related to used_bmap field in BDRVParallelsState and is created only for
+     * local usage.
+     *
      * If a bit is set, there is a BAT entry pointing to this cluster.
      * Loop through the BAT entries, check bits relevant to an entry offset.
      * If bit is set, this entry is duplicated. Otherwise set the bit.
-- 
2.34.1