Re: [Qemu-devel] [PATCH 1/1] Support default interface types per QEMUMachine

[Alexander Graf]

On 26.04.2012, at 21:00, Christian Borntraeger wrote:

> On 26/04/12 19:11, Peter Maydell wrote:
>> On 26 April 2012 18:09, Alexander Graf <address@hidden> wrote:
>>> On 26.04.2012, at 18:17, Peter Maydell wrote:
>>>> Can you describe what the problem is that you're trying to solve
>>>> here? It's not entirely obvious from this commit message.
>>> 
>>> On s390, there is no ide or scsi, so qemu-system-s390x <file> currently
>>> uses a dirty hack that loops through IF_IDE and creates virtio devices.
>>> I'd assume this patch tried to get rid of that.
>> 
>> What's wrong with just having it be an error if the user
>> creates IDE drives for a machine with no IDE interfaces?
> 
> For example the fact that drive file=xxx works on x86  but fails on s390 if
> I remove the hack in s390_init ;-)
> 
> To me that looks more incosistent than having the right default interface even
> if "right" changes across hardware.
> If you have a second look, we already have different interfaces for different 
> systems.
> e.g. sparc defaults to scsi, pc to ide. 
> 
> So this patch will allow that s390 chooses IF_VIRTIO and exynos can choose 
> IF_SD.

Yup, and I'm definitely in favor of the change. It's good to make the normal 
command line easy. I usually want "qemu-system-foo <disk>" to give me a useful 
VM, not an error message that I can't create an IDE bus because my machine 
model doesn't even know what MMIO is ;).

And yes, we already do have the flag "use_scsi", so this is just a logic step 
further down the road. I don't see an issue with it really.


Alex