Re: [Qemu-devel] [PATCH v3] fw_cfg: RFQDN rules, documentation

[Markus Armbruster]

"Michael S. Tsirkin" <address@hidden> writes:

> On Wed, Apr 13, 2016 at 10:59:35AM +0200, Markus Armbruster wrote:
>> I have a hard time coming up with realistic unclean breakage.
>
> The issue is that Linux is now exposing fw cfg to userspace.
> So it's use is about to expand significantly.
>
> This is what I am trying to prevent:
> - in 2016, users build a guest using a path XXX outside opt.
>   there's a warning on host, but it is not noticed.

Amend:

    The guest treats path XXX as optional.

> - in 2020, qemu starts using path XXX for internal purposes.
> - using guest from 2016 now breaks uncleanly on this new qemu

Amend:

    when we're not specifying the optional path XXX with -fw_cfg.

>   since guest thinks it's talking to the external tool.

Okay, that's a much more plausible scenario.  The question remains
whether preventing it justifies the compat break and the additional
interface complexity.