dirty-bitmap: add bdrv_dirty_bitmap_next_dirty_area

The function alters bdrv_dirty_iter_next_area(), which is wrong and
less efficient (see further commit
"block/mirror: fix and improve do_sync_target_write" for description).

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

block/dirty-bitmap.c

@@ -787,6 +787,12 @@ int64_t bdrv_dirty_bitmap_next_zero(BdrvDirtyBitmap *bitmap, uint64_t offset,
     return hbitmap_next_zero(bitmap->bitmap, offset, bytes);
 }
 
+bool bdrv_dirty_bitmap_next_dirty_area(BdrvDirtyBitmap *bitmap,
+                                       uint64_t *offset, uint64_t *bytes)
+{
+    return hbitmap_next_dirty_area(bitmap->bitmap, offset, bytes);
+}
+
 void bdrv_merge_dirty_bitmap(BdrvDirtyBitmap *dest, const BdrvDirtyBitmap *src,
                              HBitmap **backup, Error **errp)
 {

include/block/dirty-bitmap.h

@@ -101,6 +101,8 @@ BdrvDirtyBitmap *bdrv_dirty_bitmap_next(BlockDriverState *bs,
 char *bdrv_dirty_bitmap_sha256(const BdrvDirtyBitmap *bitmap, Error **errp);
 int64_t bdrv_dirty_bitmap_next_zero(BdrvDirtyBitmap *bitmap, uint64_t offset,
                                     uint64_t bytes);
+bool bdrv_dirty_bitmap_next_dirty_area(BdrvDirtyBitmap *bitmap,
+                                       uint64_t *offset, uint64_t *bytes);
 BdrvDirtyBitmap *bdrv_reclaim_dirty_bitmap_locked(BlockDriverState *bs,
                                                   BdrvDirtyBitmap *bitmap,
                                                   Error **errp);

include/qemu/hbitmap.h

@@ -311,6 +311,22 @@ unsigned long hbitmap_iter_skip_words(HBitmapIter *hbi);
  */
 int64_t hbitmap_next_zero(const HBitmap *hb, uint64_t start, uint64_t count);
 
+/* hbitmap_next_dirty_area:
+ * @hb: The HBitmap to operate on
+ * @start: in-out parameter.
+ *         in: the offset to start from
+ *         out: (if area found) start of found area
+ * @count: in-out parameter.
+ *         in: length of requested region
+ *         out: length of found area
+ *
+ * If dirty area found within [@start, @start + @count), returns true and sets
+ * @offset and @bytes appropriately. Otherwise returns false and leaves @offset
+ * and @bytes unchanged.
+ */
+bool hbitmap_next_dirty_area(const HBitmap *hb, uint64_t *start,
+                             uint64_t *count);
+
 /* hbitmap_create_meta:
  * Create a "meta" hbitmap to track dirtiness of the bits in this HBitmap.
  * The caller owns the created bitmap and must call hbitmap_free_meta(hb) to

util/hbitmap.c

@@ -246,6 +246,45 @@ int64_t hbitmap_next_zero(const HBitmap *hb, uint64_t start, uint64_t count)
     return res;
 }
 
+bool hbitmap_next_dirty_area(const HBitmap *hb, uint64_t *start,
+                             uint64_t *count)
+{
+    HBitmapIter hbi;
+    int64_t firt_dirty_off, area_end;
+    uint32_t granularity = 1UL << hb->granularity;
+    uint64_t end;
+
+    if (*start >= hb->orig_size || *count == 0) {
+        return false;
+    }
+
+    end = *count > hb->orig_size - *start ? hb->orig_size : *start + *count;
+
+    hbitmap_iter_init(&hbi, hb, *start);
+    firt_dirty_off = hbitmap_iter_next(&hbi, false);
+
+    if (firt_dirty_off < 0 || firt_dirty_off >= end) {
+        return false;
+    }
+
+    if (firt_dirty_off + granularity >= end) {
+        area_end = end;
+    } else {
+        area_end = hbitmap_next_zero(hb, firt_dirty_off + granularity,
+                                     end - firt_dirty_off - granularity);
+        if (area_end < 0) {
+            area_end = end;
+        }
+    }
+
+    if (firt_dirty_off > *start) {
+        *start = firt_dirty_off;
+    }
+    *count = area_end - *start;
+
+    return true;
+}
+
 bool hbitmap_empty(const HBitmap *hb)
 {
     return hb->count == 0;