Re: [Xen-devel] [Qemu-devel] Project idea: make QEMU more flexible

[Anthony Liguori <anthony@xxxxxxxxxxxxx>]

On Mon, Jan 6, 2014 at 7:57 AM, Stefano Stabellini
<stefano.stabellini@xxxxxxxxxxxxx> wrote:
> On Mon, 6 Jan 2014, Anthony Liguori wrote:
>> On Jan 6, 2014 6:55 AM, "Stefano Stabellini" 
>> <stefano.stabellini@xxxxxxxxxxxxx> wrote:
>> >
>> > On Mon, 6 Jan 2014, Anthony Liguori wrote:
>> > > On Jan 6, 2014 6:23 AM, "Peter Maydell" <peter.maydell@xxxxxxxxxx> wrote:
>> > > >
>> > > > On 6 January 2014 14:17, Stefano Stabellini
>> > > > <stefano.stabellini@xxxxxxxxxxxxx> wrote:
>> > > > > It doesn't do any emulation so it is not specific to any 
>> > > > > architecture or
>> > > > > any cpu.
>> > > >
>> > > > You presumably still care about the compiled in values of
>> > > > TARGET_WORDS_BIGENDIAN, TARGET_LONG_SIZE, and so on...
>> >
>> > Actually it only uses XC_PAGE_SIZE and the endianness is the host
>> > endianness.
>>
>> If blkif in QEMU is relying on host endianness thats a bug.
>
> Why? Xen doesn't support a different guest/host endianness.

For the same reason that the virtio devices do not rely on host endianness.

It should be possible to use the Xen devices with TCG.  It isn't today
simply because the code wasn't structured that way but it could be
refactored to do this.

>> > > Yup.  It's still accel=xen just with no VCPUs.
>> >
>> > Are you talking about introducing accel=xen to Wei's target-null?
>> > I guess that would work OK.
>>
>> We already have accel=xen.  I'm echoing Peter's suggestion of having the 
>> ability to compile out accel=tcg.
>>
>> >
>> > On the other hand if you are thinking of avoiding the introduction of a
>> > new target-null, how would you make xen_machine_pv.c available to
>> > multiple architectures?
>>
>> Why does qdisk need a full machine?
>
> qdisk is just one device, xen_machine_pv is the machine that initializes
> the backend infrastructure (one of the backends is qdisk).
> It doesn't make sense to use a full-blown machine like pc.c just to
> start few backends, right?

What prevents xen_machine_pv from being compiled for multiple targets?
 If there i386 specific things in it, they surely could be refactored
a bit, no?

Regards,

Anthony Liguori

>
>
>> How would you avoid the compilation of all the
>> > unnecessary emulated devices?
>>
>> Device config files.

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