block/block-copy: always align copied region to cluster size

Since commit 42ac214406e0 (block/block-copy: refactor task creation)
block_copy_task_create calculates the area to be copied via
bdrv_dirty_bitmap_next_dirty_area, but that can return an unaligned byte
count if the image's last cluster end is not aligned to the bitmap's
granularity.

Always ALIGN_UP the resulting bytes value to satisfy block_copy_do_copy,
which requires the 'bytes' parameter to be aligned to cluster size.

Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>
Message-Id: <20200810095523.15071-1-s.reiter@proxmox.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>

block/block-copy.c

@@ -142,6 +142,9 @@ static BlockCopyTask *block_copy_task_create(BlockCopyState *s,
         return NULL;
     }
 
+    assert(QEMU_IS_ALIGNED(offset, s->cluster_size));
+    bytes = QEMU_ALIGN_UP(bytes, s->cluster_size);
+
     /* region is dirty, so no existent tasks possible in it */
     assert(!find_conflicting_task(s, offset, bytes));