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

[Stefan Reiter <s.reiter@proxmox.com>]

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 backing 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.

Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>
---

This causes backups with unaligned image sizes to fail on the last block in my
testing (e.g. a backup job with 4k cluster size fails on a drive with 4097
bytes).

Alternatively one could remove the
  assert(QEMU_IS_ALIGNED(bytes, s->cluster_size));
from block_copy_do_copy, but I'd wager that's there for a reason?

 block/block-copy.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/block/block-copy.c b/block/block-copy.c
index f7428a7c08..023cb03200 100644
--- a/block/block-copy.c
+++ b/block/block-copy.c
@@ -142,6 +142,8 @@ static BlockCopyTask *block_copy_task_create(BlockCopyState *s,
         return NULL;
     }
 
+    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));
 
-- 
2.20.1