Re: [Xen-devel] [Qemu-devel] [PATCH] Remove hardcoded xen-platform device initialization

[Andreas Färber <afaerber@xxxxxxx>]

Am 18.06.2013 21:35, schrieb Stefano Stabellini:
> On Tue, 18 Jun 2013, Paolo Bonzini wrote:
>> Il 18/06/2013 20:56, Stefano Stabellini ha scritto:
>>> xenfv-2.0 is a bad idea, like Paolo wrote, it should be possible to just
>>> use -M pc for HVM guests and retain -M xenpv for pv guests.
>>>
>>> However it seems to me that we also need a way in libxl to find out
>>> whether QEMU is new enough for us to be able to use -M pc.
>>> We can't just assume that users will be able to figure out the magic
>>> rune they need to write in the VM config file to solve their VM crash at
>>> boot problem.
>>>
>>> We could spawn an instance of QEMU just to figure out the QEMU version
>>> but we certainly cannot do that every time we start a new VM.
>>> Once we figure out the QEMU version the first time we could write it to
>>> xenstore so that the next time we don't have to go through the same
>>> process again.
>>
>> Can you just assume that 4.4 requires QEMU 1.6 or newer?
> 
> I would rather not make that assumption because we cannot control what
> distro are going to package. I wouldn't want a distro to ship with Xen
> HVM guests broken because they choose the wrong QEMU version. Of course
> we could put that in the release notes, but there are lots of distros
> out there and I am pretty sure that at least one of them is not going to
> read them.

You could check for existence of the pc-i440fx-1.6 machine and infer
that it is at least v1.6 (might break in some distant future of course
and for current git commits until your changes get merged).

Andreas

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