Re: [qemu-s390x] [PATCH v7 05/12] s390-ccw: move auxiliary IPL data to separate location

[Viktor Mihajlovski]

On 17.02.2018 09:11, Thomas Huth wrote:
[...]
> 
> I still think that the information should *not* be stored within the
> IplParameterBlock to avoid that we pass it via DIAG 0x308, too.
> If we do it like this, I'm pretty sure that we will look at this code in
> a couple of years and wonder whether we can change it again or whether
> this is an established interface between the host and the guest. So
> please, let's avoid establishing such "hidden" interfaces just out of
> current convenience. There must be a better location for this.
> Christian, do you have an idea?
> 
>  Thomas
> 
In principle I do agree, although I think we can manage the host/guest
boundary. If we believe we can't, we have a much bigger problem (looking
at the position of the iplb smack in the middle of the s390-ipl state).

The main reason why I didn't bother to introduce a new private field in
s390-ipl was that I expect more changes to the IPL area in the future
(earlier than in a couple of years) and am not really sure whether this
QEMU <-> BIOS interface will remain the same and how much effort to
spend on it.

The major point of this change is to move non-standard data out of the
guest-visible IPLB to avoid compatibility problems in the future, while
still catering for features like network boot and boot menus. I have no
bias against other solutions achieving this objective. If you and
Christian think we need a new field, it's all right with me.

-- 
Regards,
 Viktor Mihajlovski