Re: [Qemu-devel] On block interface types in general, IF_AHCI in particular

[Anthony Liguori <anthony@codemonkey.ws>]

Kevin Wolf <kwolf@redhat.com> writes:

> Am 30.10.2012 17:31, schrieb Paolo Bonzini:
>> Il 30/10/2012 15:43, Markus Armbruster ha scritto:
>>> There's a related argument that I find more compelling: we may want
>>> if=ahci to let users choose nicely between IDE and AHCI.  Makes sense
>>> only if we have boards providing both kind of controllers onboard.  q35
>>> doesn't.
>> 
>> I think the main problem is that we haven't hashed out the requirements.
>>  Since this is QEMU and not libvirt (which uses -drive if=none / -device
>> anyway), I suppose we mostly care about direct command-line start.  We
>> want "qemu-kvm winxp.img" to work, even if q35 is now the default
>> machine.  This calls for making IDE (not AHCI) the default.
>
> Yes. I think this is my main requirement: Command lines that work with
> 1.2 should usually keep working with whatever version introduces Q35 as
> the default.
>
>> The main drawback of if=ahci is, as pointed out by Markus, that you
>> would have to provide both controllers on-board.  I think a real ICH9
>> has the compatibility IDE controller on a separate PCI address from the
>> SATA controller, so creating both of them is not really out of question.
>>  Obvious disadvantage, it would depart from real hardware.  Linux should
>> not care, not sure about SeaBIOS and Windows.
>
> Okay, so I guess the next step is finding out how real hardware works.
> Markus claims that there's no IDE mode on Q35 boards. I find this hard
> to believe and a quick search indeed suggests otherwise.
>
> What you're saying is that PCI addresses might be different for IDE and
> SATA mode, but on real hardware only one interface is exposed at the
> same time, right? This matches better what I remember, but we'd have to
> check the details.
>
>> At the same time, if all we want is a quick way to switch between IDE
>> and AHCI, we could just use machine types.  So another proposal is to
>> have two machine types, one for ICH9-IDE (pc, the default), one for
>> ICH9-AHCI (q35), one for PIIX3-IDE (piix3).  Each QEMU release would add
>> (up to) three machine types.
>
> I actually kind of like this solution.

A related option which I had previously suggested is a machine option of
"storage".

So you can do:

qemu --machine q35,storage=ide
qemu --machine i440fx,storage=scsi
qemu --machine i440fx,storage=virtio

etc.

I think it's rare that users want to have multiple storage types.  They
probably this level of granularity.

Regards,

Anthony Liguori

>
> Kevin