block/dirty-bitmap: Add bdrv_dirty_iter_next_area

This new function allows to look for a consecutively dirty area in a
dirty bitmap.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Message-id: 20180613181823.13618-10-mreitz@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>

block/dirty-bitmap.c

@@ -522,6 +522,61 @@ int64_t bdrv_dirty_iter_next(BdrvDirtyBitmapIter *iter)
     return hbitmap_iter_next(&iter->hbi, true);
 }
 
+/**
+ * Return the next consecutively dirty area in the dirty bitmap
+ * belonging to the given iterator @iter.
+ *
+ * @max_offset: Maximum value that may be returned for
+ *              *offset + *bytes
+ * @offset:     Will contain the start offset of the next dirty area
+ * @bytes:      Will contain the length of the next dirty area
+ *
+ * Returns: True if a dirty area could be found before max_offset
+ *          (which means that *offset and *bytes then contain valid
+ *          values), false otherwise.
+ *
+ * Note that @iter is never advanced if false is returned.  If an area
+ * is found (which means that true is returned), it will be advanced
+ * past that area.
+ */
+bool bdrv_dirty_iter_next_area(BdrvDirtyBitmapIter *iter, uint64_t max_offset,
+                               uint64_t *offset, int *bytes)
+{
+    uint32_t granularity = bdrv_dirty_bitmap_granularity(iter->bitmap);
+    uint64_t gran_max_offset;
+    int64_t ret;
+    int size;
+
+    if (max_offset == iter->bitmap->size) {
+        /* If max_offset points to the image end, round it up by the
+         * bitmap granularity */
+        gran_max_offset = ROUND_UP(max_offset, granularity);
+    } else {
+        gran_max_offset = max_offset;
+    }
+
+    ret = hbitmap_iter_next(&iter->hbi, false);
+    if (ret < 0 || ret + granularity > gran_max_offset) {
+        return false;
+    }
+
+    *offset = ret;
+    size = 0;
+
+    assert(granularity <= INT_MAX);
+
+    do {
+        /* Advance iterator */
+        ret = hbitmap_iter_next(&iter->hbi, true);
+        size += granularity;
+    } while (ret + granularity <= gran_max_offset &&
+             hbitmap_iter_next(&iter->hbi, false) == ret + granularity &&
+             size <= INT_MAX - granularity);
+
+    *bytes = MIN(size, max_offset - *offset);
+    return true;
+}
+
 /* Called within bdrv_dirty_bitmap_lock..unlock */
 void bdrv_set_dirty_bitmap_locked(BdrvDirtyBitmap *bitmap,
                                   int64_t offset, int64_t bytes)

include/block/dirty-bitmap.h

@@ -82,6 +82,8 @@ void bdrv_set_dirty_bitmap_locked(BdrvDirtyBitmap *bitmap,
 void bdrv_reset_dirty_bitmap_locked(BdrvDirtyBitmap *bitmap,
                                     int64_t offset, int64_t bytes);
 int64_t bdrv_dirty_iter_next(BdrvDirtyBitmapIter *iter);
+bool bdrv_dirty_iter_next_area(BdrvDirtyBitmapIter *iter, uint64_t max_offset,
+                               uint64_t *offset, int *bytes);
 void bdrv_set_dirty_iter(BdrvDirtyBitmapIter *hbi, int64_t offset);
 int64_t bdrv_get_dirty_count(BdrvDirtyBitmap *bitmap);
 int64_t bdrv_get_meta_dirty_count(BdrvDirtyBitmap *bitmap);