Add a helper to set unused areas in used bitmap.

Signed-off-by: Alexander Ivanov <alexander.ivanov@virtuozzo.com>
---
 block/parallels.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/block/parallels.c b/block/parallels.c
index 7eb92f87ab..6a4e3945c6 100644
--- a/block/parallels.c
+++ b/block/parallels.c
@@ -195,6 +195,23 @@ static int mark_used(BlockDriverState *bs, unsigned long *bitmap,
     return 0;
 }
 
+static int mark_unused(BlockDriverState *bs, unsigned long *bitmap,
+                       uint32_t bitmap_size, int64_t off, uint32_t count)
+{
+    BDRVParallelsState *s = bs->opaque;
+    uint32_t cluster_index = host_cluster_index(s, off);
+    unsigned long next_unused;
+    if (cluster_index + count > bitmap_size) {
+        return -E2BIG;
+    }
+    next_unused = find_next_zero_bit(bitmap, bitmap_size, cluster_index);
+    if (next_unused < cluster_index + count) {
+        return -EINVAL;
+    }
+    bitmap_clear(bitmap, cluster_index, count);
+    return 0;
+}
+
 /*
  * Collect used bitmap. The image can contain errors, we should fill the
  * bitmap anyway, as much as we can. This information will be used for
-- 
2.34.1