dirty-bitmap: improve bdrv_dirty_bitmap_next_zero

Add bytes parameter to the function, to limit searched range.

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

block/backup.c

@@ -422,7 +422,8 @@ static void backup_incremental_init_copy_bitmap(BackupBlockJob *job)
             break;
         }
 
-        offset = bdrv_dirty_bitmap_next_zero(job->sync_bitmap, offset);
+        offset = bdrv_dirty_bitmap_next_zero(job->sync_bitmap, offset,
+                                             UINT64_MAX);
         if (offset == -1) {
             hbitmap_set(job->copy_bitmap, cluster, end - cluster);
             break;

block/dirty-bitmap.c

@@ -781,9 +781,10 @@ char *bdrv_dirty_bitmap_sha256(const BdrvDirtyBitmap *bitmap, Error **errp)
     return hbitmap_sha256(bitmap->bitmap, errp);
 }
 
-int64_t bdrv_dirty_bitmap_next_zero(BdrvDirtyBitmap *bitmap, uint64_t offset)
+int64_t bdrv_dirty_bitmap_next_zero(BdrvDirtyBitmap *bitmap, uint64_t offset,
+                                    uint64_t bytes)
 {
-    return hbitmap_next_zero(bitmap->bitmap, offset);
+    return hbitmap_next_zero(bitmap->bitmap, offset, bytes);
 }
 
 void bdrv_merge_dirty_bitmap(BdrvDirtyBitmap *dest, const BdrvDirtyBitmap *src,

include/block/dirty-bitmap.h

@@ -99,7 +99,8 @@ bool bdrv_has_changed_persistent_bitmaps(BlockDriverState *bs);
 BdrvDirtyBitmap *bdrv_dirty_bitmap_next(BlockDriverState *bs,
                                         BdrvDirtyBitmap *bitmap);
 char *bdrv_dirty_bitmap_sha256(const BdrvDirtyBitmap *bitmap, Error **errp);
-int64_t bdrv_dirty_bitmap_next_zero(BdrvDirtyBitmap *bitmap, uint64_t start);
+int64_t bdrv_dirty_bitmap_next_zero(BdrvDirtyBitmap *bitmap, uint64_t offset,
+                                    uint64_t bytes);
 BdrvDirtyBitmap *bdrv_reclaim_dirty_bitmap_locked(BlockDriverState *bs,
                                                   BdrvDirtyBitmap *bitmap,
                                                   Error **errp);

include/qemu/hbitmap.h

@@ -300,12 +300,16 @@ void hbitmap_iter_init(HBitmapIter *hbi, const HBitmap *hb, uint64_t first);
 unsigned long hbitmap_iter_skip_words(HBitmapIter *hbi);
 
 /* hbitmap_next_zero:
+ *
+ * Find next not dirty bit within selected range. If not found, return -1.
+ *
  * @hb: The HBitmap to operate on
  * @start: The bit to start from.
- *
- * Find next not dirty bit.
+ * @count: Number of bits to proceed. If @start+@count > bitmap size, the whole
+ * bitmap is looked through. You can use UINT64_MAX as @count to search up to
+ * the bitmap end.
  */
-int64_t hbitmap_next_zero(const HBitmap *hb, uint64_t start);
+int64_t hbitmap_next_zero(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.

nbd/server.c

@@ -2014,7 +2014,7 @@ static unsigned int bitmap_to_extents(BdrvDirtyBitmap *bitmap, uint64_t offset,
         bool next_dirty = !dirty;
 
         if (dirty) {
-            end = bdrv_dirty_bitmap_next_zero(bitmap, begin);
+            end = bdrv_dirty_bitmap_next_zero(bitmap, begin, UINT64_MAX);
         } else {
             bdrv_set_dirty_iter(it, begin);
             end = bdrv_dirty_iter_next(it);

tests/test-hbitmap.c

@@ -939,7 +939,7 @@ static void test_hbitmap_iter_and_reset(TestHBitmapData *data,
 
 static void test_hbitmap_next_zero_check(TestHBitmapData *data, int64_t start)
 {
-    int64_t ret1 = hbitmap_next_zero(data->hb, start);
+    int64_t ret1 = hbitmap_next_zero(data->hb, start, UINT64_MAX);
     int64_t ret2 = start;
     for ( ; ret2 < data->size && hbitmap_get(data->hb, ret2); ret2++) {
         ;

util/hbitmap.c

@@ -53,6 +53,9 @@
  */
 
 struct HBitmap {
+    /* Size of the bitmap, as requested in hbitmap_alloc. */
+    uint64_t orig_size;
+
     /* Number of total bits in the bottom level.  */
     uint64_t size;
 
@@ -192,16 +195,28 @@ void hbitmap_iter_init(HBitmapIter *hbi, const HBitmap *hb, uint64_t first)
     }
 }
 
-int64_t hbitmap_next_zero(const HBitmap *hb, uint64_t start)
+int64_t hbitmap_next_zero(const HBitmap *hb, uint64_t start, uint64_t count)
 {
     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);
+    unsigned start_bit_offset;
+    uint64_t end_bit, sz;
     int64_t res;
 
+    if (start >= hb->orig_size || count == 0) {
+        return -1;
+    }
+
+    end_bit = count > hb->orig_size - start ?
+                hb->size :
+                ((start + count - 1) >> hb->granularity) + 1;
+    sz = (end_bit + BITS_PER_LONG - 1) >> BITS_PER_LEVEL;
+
+    /* There may be some zero bits in @cur before @start. We are not interested
+     * in them, let's set them.
+     */
+    start_bit_offset = (start >> hb->granularity) & (BITS_PER_LONG - 1);
     cur |= (1UL << start_bit_offset) - 1;
     assert((start >> hb->granularity) < hb->size);
 
@@ -218,7 +233,7 @@ int64_t hbitmap_next_zero(const HBitmap *hb, uint64_t start)
     }
 
     res = (pos << BITS_PER_LEVEL) + ctol(cur);
-    if (res >= hb->size) {
+    if (res >= end_bit) {
         return -1;
     }
 
@@ -652,6 +667,8 @@ HBitmap *hbitmap_alloc(uint64_t size, int granularity)
     HBitmap *hb = g_new0(struct HBitmap, 1);
     unsigned i;
 
+    hb->orig_size = size;
+
     assert(granularity >= 0 && granularity < 64);
     size = (size + (1ULL << granularity) - 1) >> granularity;
     assert(size <= ((uint64_t)1 << HBITMAP_LOG_MAX_SIZE));