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

From: Alberto Garcia
Subject: Re: [Qemu-devel] [PATCH for-3.1 v10 04/31] block: Add BDS.auto_backing_file
Date: Wed, 05 Sep 2018 16:22:20 +0200
User-agent: Notmuch/0.18.2 (http://notmuchmail.org) Emacs/24.4.1 (i586-pc-linux-gnu)

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?


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