Re: [Qemu-devel] [PATCH for-1.6] pc: fix up pc initialization

["Andreas Färber" <afaerber@suse.de>]

Am 13.08.2013 16:54, schrieb Paolo Bonzini:
> Il 13/08/2013 16:11, Anthony Liguori ha scritto:
>>>> Fix this up, clean up a trivial code duplication
>>>> and add a comment explaining why we special-case 1.5
>>>> with respect to pvpanic.
>>>>
>>>> Reported-by: Markus Armbruster <armbru@redhat.com>
>>>> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
>> Thanks for catching this.  I'm a little disturbed by this.  I use git-am
>> --3way specifically to avoid problems from fuzzing but I guess merge
>> artifacts are possible.
>>
> 
> I wonder if we shouldn't disable pvpanic in 1.5 too, one-off behavior is
> ugly and likely no one will notice.

I had rejected the previous attempt to completely disable pvpanic device
because it looked to me as if this compatibility aspect had been
forgotten. I didn't imagine the resulting code to look as ugly though,
with us "skipping" _1_5 to not have 1.5 overwrite has_pvpanic for 1.6+.

mst suggested to patch stable-1.5 to disable it there, too. I am not
against but have doubts as to how well that works with migration, since
1.5.3 is still a bit off and I would expect 1.5.2 -> 1.6.0 migration to
work without guest-visible changes... We could argue that having to use
-M pc-i440fx-1.5 we can also expect users to add -device pvpanic;
question would be how to convey that knowledge of
if-you-use-pc-x.y-then-you-also-need-to-do-Z to users, which
compat_props usually handle under the hood. We could misuse
pvpanic.ioport=0 for that purpose until we have a better solution.

Regards,
Andreas

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