qcow2: Switch load_bitmap_data() to byte-based iteration

Now that we have adjusted the majority of the calls this function
makes to be byte-based, it is easier to read the code if it makes
passes over the image using bytes rather than sectors.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/qcow2-bitmap.c

@@ -291,9 +291,8 @@ static int load_bitmap_data(BlockDriverState *bs,
 {
     int ret = 0;
     BDRVQcow2State *s = bs->opaque;
-    uint64_t sector, limit, sbc;
+    uint64_t offset, limit;
     uint64_t bm_size = bdrv_dirty_bitmap_size(bitmap);
-    uint64_t bm_sectors = DIV_ROUND_UP(bm_size, BDRV_SECTOR_SIZE);
     uint8_t *buf = NULL;
     uint64_t i, tab_size =
             size_to_clusters(s,
@@ -305,32 +304,27 @@ static int load_bitmap_data(BlockDriverState *bs,
 
     buf = g_malloc(s->cluster_size);
     limit = bytes_covered_by_bitmap_cluster(s, bitmap);
-    sbc = limit >> BDRV_SECTOR_BITS;
-    for (i = 0, sector = 0; i < tab_size; ++i, sector += sbc) {
-        uint64_t count = MIN(bm_sectors - sector, sbc);
+    for (i = 0, offset = 0; i < tab_size; ++i, offset += limit) {
+        uint64_t count = MIN(bm_size - offset, limit);
         uint64_t entry = bitmap_table[i];
-        uint64_t offset = entry & BME_TABLE_ENTRY_OFFSET_MASK;
+        uint64_t data_offset = entry & BME_TABLE_ENTRY_OFFSET_MASK;
 
         assert(check_table_entry(entry, s->cluster_size) == 0);
 
-        if (offset == 0) {
+        if (data_offset == 0) {
             if (entry & BME_TABLE_ENTRY_FLAG_ALL_ONES) {
-                bdrv_dirty_bitmap_deserialize_ones(bitmap,
-                                                   sector * BDRV_SECTOR_SIZE,
-                                                   count * BDRV_SECTOR_SIZE,
+                bdrv_dirty_bitmap_deserialize_ones(bitmap, offset, count,
                                                    false);
             } else {
                 /* No need to deserialize zeros because the dirty bitmap is
                  * already cleared */
             }
         } else {
-            ret = bdrv_pread(bs->file, offset, buf, s->cluster_size);
+            ret = bdrv_pread(bs->file, data_offset, buf, s->cluster_size);
             if (ret < 0) {
                 goto finish;
             }
-            bdrv_dirty_bitmap_deserialize_part(bitmap, buf,
-                                               sector * BDRV_SECTOR_SIZE,
-                                               count * BDRV_SECTOR_SIZE,
+            bdrv_dirty_bitmap_deserialize_part(bitmap, buf, offset, count,
                                                false);
         }
     }