Re: [PATCH 3/6] qemu-img: rebase: use backing files' BlockBackend for buffer alignment

[Hanna Czenczek]

On 01.06.23 21:28, Andrey Drobyshev via wrote:
> Since commit bb1c05973cf ("qemu-img: Use qemu_blockalign"), buffers for
> the data read from the old and new backing files are aligned using
> BlockDriverState (or BlockBackend later on) referring to the target image.
> However, this isn't quite right, because target image is only being
> written to and has nothing to do with those buffers.  Let's fix that.

I don’t understand.  The write to the target image does use one of those 
buffers (buf_old, specifically).

This change is correct for buf_new/blk_new_backing, but for buf_old, in 
theory, we need a buffer that fulfills both the alignment requirements 
of blk and blk_old_backing.  (Not that this patch really makes the 
situation worse for buf_old.)

Hanna