Re: [Qemu-devel] [PATCH 6/6] hw/i386/i386: Stop auto-creating lsi53c895a SCSI HBAs

[Paolo Bonzini <pbonzini@redhat.com>]

On 23/01/2017 20:16, Markus Armbruster wrote:
>>                                                      Could we change
>> those messages to errors
> 
> Fine with me, but when it comes to arguing for backward compatibility of
> our byzantine command line, I'm kind of like a lethargic public defender
> with an overly deep relationship to Bourbon.  "Your honor, sure capital
> punishment is called for?  Yes?  Okay then."
> 
> I vaguely recall discussing the topic with Peter (cc'ed).  If memory
> serves, one concern was breaking usage of -device with -drive lacking
> if=...  Works fine (no warning) with machines that don't pick up drives
> with their default block interface type, i.e. most of them.  But PATCH 3
> changes their default to if=none, so that usage wouldn't actually break.

I think that tips the scale in favor of having errors.

> What would break is -device with -drive if=T, where T is not none and
> not picked up by the board.  Such usage is certainly questionable[*],
> but it's questionable enough for us to break it?
> 
>>                          and then drop PC if=scsi support altogether?
> 
> Different backward compatibility question: here we break usage of
> if=scsi with PC machine types.  Legacy way to do things, but it's
> documented in qemu.1.  Are we happy to break it?

That usage is wrong after this patch, since it mentions
qemu-system-i386.  So it's documented, but almost useless and the
example is not exactly correct.  Let's deprecate it in 2.9 and remove in
2.10.

Paolo