3 files changed, 16 insertions, 2 deletions
diff --git a/block.c b/block.c
index 1919d19732..e9fd8808bb 100644
--- a/block.c
+++ b/block.c
@@ -686,9 +686,15 @@ static void set_dirty_bitmap(BlockDriverState *bs, int64_t sector_num,
         bit = start % (sizeof(unsigned long) * 8);
         val = bs->dirty_bitmap[idx];
         if (dirty) {
-            val |= 1 << bit;
+            if (!(val & (1 << bit))) {
+                bs->dirty_count++;
+                val |= 1 << bit;
+            }
         } else {
-            val &= ~(1 << bit);
+            if (val & (1 << bit)) {
+                bs->dirty_count--;
+                val &= ~(1 << bit);
+            }
         }
         bs->dirty_bitmap[idx] = val;
     }
@@ -2139,6 +2145,7 @@ void bdrv_set_dirty_tracking(BlockDriverState *bs, int enable)
 {
     int64_t bitmap_size;
 
+    bs->dirty_count = 0;
     if (enable) {
         if (!bs->dirty_bitmap) {
             bitmap_size = (bdrv_getlength(bs) >> BDRV_SECTOR_BITS) +
@@ -2173,3 +2180,8 @@ void bdrv_reset_dirty(BlockDriverState *bs, int64_t cur_sector,
 {
     set_dirty_bitmap(bs, cur_sector, nr_sectors, 0);
 }
+
+int64_t bdrv_get_dirty_count(BlockDriverState *bs)
+{
+    return bs->dirty_count;
+}
diff --git a/block.h b/block.h
index ecf66c52ab..536265e86c 100644
--- a/block.h
+++ b/block.h
@@ -200,4 +200,5 @@ void bdrv_set_dirty_tracking(BlockDriverState *bs, int enable);
 int bdrv_get_dirty(BlockDriverState *bs, int64_t sector);
 void bdrv_reset_dirty(BlockDriverState *bs, int64_t cur_sector,
                       int nr_sectors);
+int64_t bdrv_get_dirty_count(BlockDriverState *bs);
 #endif
diff --git a/block_int.h b/block_int.h
index a0ebd90a0b..223a437b6a 100644
--- a/block_int.h
+++ b/block_int.h
@@ -175,6 +175,7 @@ struct BlockDriverState {
     int type;
     char device_name[32];
     unsigned long *dirty_bitmap;
+    int64_t dirty_count;
     BlockDriverState *next;
     void *private;
 };