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

[Alberto Garcia]

On Fri 07 Sep 2018 02:42:53 PM CEST, Max Reitz wrote:
> The whole purpose of bs->auto_backing_file is so you can compare it
> with bs->backing->bs->filename, see when it differs, and then you know
> that the user has changed the backing file from what it would be based
> on the image header alone (that is, if the user hadn't specified any
> @backing option at all).
  [...]
> (Now you could ask yourself, if we know the user hasn't specified any
> options to override the backing file -- why don't we just store a
> flag?  I tried that, Kevin wasn't really happy about it because it's
> hard to catch all corner cases.  There are many ways to change a
> backing file, and if you want to find out when a backing file has been
> changed to exactly what the image header says (this is the ideal
> outcome of the commit block job, for instance), you basically get back
> to the same problem of comparing filenames.)

Ok, I think this clarifies a lot. Thanks!

Berto