Re: [Qemu-devel] [PATCH for-3.1 v10 04/31] block: Add BDS.auto_backing_file

[Alberto Garcia]

On Thu 09 Aug 2018 11:35:01 PM CEST, Max Reitz wrote:
> If the backing file is overridden, this most probably does change the
> guest-visible data of a BDS.  Therefore, we will need to consider this
> in bdrv_refresh_filename().
>
> To see whether it has been overridden, we might want to compare
> bs->backing_file and bs->backing->bs->filename.  However,
> bs->backing_file is changed by bdrv_set_backing_hd() (which is just used
> to change the backing child at runtime, without modifying the image
> header), so bs->backing_file most of the time simply contains a copy of
> bs->backing->bs->filename anyway, so it is useless for such a
> comparison.

What's the point of bs->backing_file then? In what cases is it different
from backing->bs->filename?

Berto