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Re: [Xen-devel] is it possible to build two privileged domain at boot time?

  • To: "文成建" <wenchengjian@xxxxxxxxxxxxxxx>
  • From: "Derek Murray" <Derek.Murray@xxxxxxxxxxxx>
  • Date: Mon, 2 Jun 2008 15:35:09 +0100
  • Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Mon, 02 Jun 2008 07:35:31 -0700
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  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>

Hi Dowen,

Okay - this might prove to be an interesting effort!

I assume you're seeing panics in construct_dom0, the second time that
you call it.

First of all, I presume that you've removed this line:

    /* Sanity! */
    BUG_ON(d->domain_id != 0);

...which will cause a bug in the hypervisor at the second instance of
calling it.

Your reference to the ELF image being changed might be to do with this line:

    /* Free temporary buffers. */

...also in construct_dom0. The second time round, these buffers will
have been freed, which is probably why you're getting garbage for the
second domain. So you'll want to move this out into the calling

Hope this helps, and let me know how you get it.



2008/6/2 文成建 <wenchengjian@xxxxxxxxxxxxxxx>:
> Hi Derek,
> Thank you very much for your response. Your suggestion helps me a lot.
> What you said at the very beginning of your mail is exactly what I want
> for my purpose.
> Though it is not ideal method I'd like to implement it to train myself
> on xen technology.
> Soon later maybe I'll be able to implement the method you suggest.
> Now I am trying to build two privileged domain mainly by calling
> /*construct_dom0*/ two times
> at the fuction of /*__start_xen. */ I realized that the reason for panic
> is orginal domain0 kernel image has been changed
> after construct_dom0. But I can't find how it has been changed. If I
> know the details I can avoid the step changing the elf image
> or I can prepare the elf image once again. Right?
> I need your help about it. Thanks in advance!
> Regards,
> Dowen
> Derek Murray 写道:
>> Hi Dowen,
>> It would be possible to create two privileged domains at boot time (by
>> modifying the hypervisor to make it possible for the domain builder to
>> create more than one initial domain; or you could add a privileged
>> hypercall to make other domains privileged, and modify the domain
>> builder in Dom0). However, I'm not sure that this is what you would
>> want for your purposes.
>> If Dom0 crashes, it typically brings down the whole physical machine,
>> because Dom0 is responsible for managing various parts of the physical
>> platform. Therefore, I don't think it would be straightforward to
>> perform failover to a second Dom0 in the event of the primary Dom0
>> crashing.
>> Perhaps a better idea would be to have a stripped-down Linux that acts
>> as Dom0 for managing the platform, but which has no user-space
>> applications or device drivers (and therefore would be much less
>> likely to shut down unexpectedly). Then you could use PCI device
>> passthrough to a second privileged domain (say, Dom1), which then runs
>> the management software and hosts the physical device drivers.
>> Although it wouldn't be bulletproof (since a malfunctioning device
>> driver could probably still hose the entire system, unless you use
>> VT-d or similar), you could probably restart Dom1 if it crashed. You'd
>> need to modify some of the tools to make things like XenStore (which
>> holds configuration details for the domains) persist across reboots.
>> You might also benefit from looking at the domain save/restore code so
>> that, if Dom1 crashes, all domains would be paused while it is
>> rebooted, and restored when it is running again.
>> Regards,
>> Derek Murray.
>> On Thu, May 29, 2008 at 5:55 PM, 文成建 <wenchengjian@xxxxxxxxxxxxxxx> wrote:
>>> Hi All,
>>>   I am not very familiar with xen details. Now I am thinking of building two
>>> privilged domain(domain 0 not driver domain) at boot time.
>>> The other question is that wether i se
>>> when domain 0 is shut down  unexpectedly another domain 0 can run at once.
>>> Maybe it is absurd. I am looking forwards to your suggestions.
>>> Regards,
>>> Dowen
>>> _______________________________________________
>>> Xen-devel mailing list
>>> Xen-devel@xxxxxxxxxxxxxxxxxxx
>>> http://lists.xensource.com/xen-devel

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