[Qemu-devel] [PATCH 1/6] block dirty bitmap: add next_zero function

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

The function searches for next zero bit (corresponding to next not-dirty
bit).

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 block/dirty-bitmap.c         |  5 +++++
 include/block/dirty-bitmap.h |  2 ++
 include/qemu/hbitmap.h       |  8 ++++++++
 util/hbitmap.c               | 26 ++++++++++++++++++++++++++
 4 files changed, 41 insertions(+)

diff --git a/block/dirty-bitmap.c b/block/dirty-bitmap.c
index 919ce10..6da27d9 100644
--- a/block/dirty-bitmap.c
+++ b/block/dirty-bitmap.c
@@ -490,3 +490,8 @@ int64_t bdrv_get_dirty_count(BdrvDirtyBitmap *bitmap)
 {
     return hbitmap_count(bitmap->bitmap);
 }
+
+int64_t bdrv_dirty_bitmap_next_zero(BdrvDirtyBitmap *bitmap, uint64_t start)
+{
+    return hbitmap_next_zero(bitmap->bitmap, start);
+}
diff --git a/include/block/dirty-bitmap.h b/include/block/dirty-bitmap.h
index 6ba5bec..0033942 100644
--- a/include/block/dirty-bitmap.h
+++ b/include/block/dirty-bitmap.h
@@ -68,4 +68,6 @@ void bdrv_dirty_bitmap_deserialize_zeroes(BdrvDirtyBitmap *bitmap,
                                           bool finish);
 void bdrv_dirty_bitmap_deserialize_finish(BdrvDirtyBitmap *bitmap);
 
+int64_t bdrv_dirty_bitmap_next_zero(BdrvDirtyBitmap *bitmap, uint64_t start);
+
 #endif
diff --git a/include/qemu/hbitmap.h b/include/qemu/hbitmap.h
index 00dbb60..852e423 100644
--- a/include/qemu/hbitmap.h
+++ b/include/qemu/hbitmap.h
@@ -259,6 +259,14 @@ void hbitmap_iter_init(HBitmapIter *hbi, const HBitmap *hb, uint64_t first);
  */
 unsigned long hbitmap_iter_skip_words(HBitmapIter *hbi);
 
+/* hbitmap_next_zero:
+ * @hb: The HBitmap to operate on
+ * @start: The bit to start from.
+ *
+ * Find next not dirty bit.
+ */
+int64_t hbitmap_next_zero(const HBitmap *hb, uint64_t start);
+
 /* 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
diff --git a/util/hbitmap.c b/util/hbitmap.c
index 1e49ab7..bcddca9 100644
--- a/util/hbitmap.c
+++ b/util/hbitmap.c
@@ -169,6 +169,32 @@ void hbitmap_iter_init(HBitmapIter *hbi, const HBitmap *hb, uint64_t first)
     }
 }
 
+int64_t hbitmap_next_zero(const HBitmap *hb, uint64_t start)
+{
+    size_t pos = (start >> hb->granularity) >> BITS_PER_LEVEL;
+    unsigned long *last_lev = hb->levels[HBITMAP_LEVELS - 1];
+    uint64_t sz = hb->sizes[HBITMAP_LEVELS - 1];
+    unsigned long cur = last_lev[pos];
+    unsigned start_bit_offset =
+            (start >> hb->granularity) & (BITS_PER_LONG - 1);
+    cur |= (1UL << start_bit_offset) - 1;
+
+    if (cur == (unsigned long)-1) {
+        do {
+            pos++;
+        } while (pos < sz && last_lev[pos] == (unsigned long)-1);
+
+        if (pos >= sz) {
+            return -1;
+        }
+
+        cur = last_lev[pos];
+    }
+
+    return MIN((pos << BITS_PER_LEVEL) + ctol(cur), hb->size - 1)
+            << hb->granularity;
+}
+
 bool hbitmap_empty(const HBitmap *hb)
 {
     return hb->count == 0;
-- 
1.8.3.1