Re: [PATCH v3 01/15] xen: add xenstore domain flag to hypervisor

From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Juergen Gross <jgross@suse.com>, Jan Beulich <JBeulich@suse.com>
Cc: wei.liu2@citrix.com, Ian.Campbell@citrix.com,
	stefano.stabellini@eu.citrix.com, Tim Deegan <tim@xen.org>,
	ian.jackson@eu.citrix.com, xen-devel@lists.xen.org,
	David Vrabel <david.vrabel@citrix.com>,
	Keir Fraser <keir@xen.org>,
	dgdegra@tycho.nsa.gov
Subject: Re: [PATCH v3 01/15] xen: add xenstore domain flag to hypervisor
Date: Fri, 8 Jan 2016 14:25:53 +0000	[thread overview]
Message-ID: <568FC6F1.2030504@citrix.com> (raw)
In-Reply-To: <568FC60F.4090605@suse.com>

On 08/01/16 14:22, Juergen Gross wrote:
> On 08/01/16 15:07, Jan Beulich wrote:
>>>>> On 08.01.16 at 14:08, <JGross@suse.com> wrote:
>>> --- a/xen/common/domain.c
>>> +++ b/xen/common/domain.c
>>> @@ -318,6 +318,12 @@ struct domain *domain_create(domid_t domid, unsigned int domcr_flags,
>>>          hardware_domain = d;
>>>      }
>>>  
>>> +    if ( domcr_flags & DOMCRF_xs_domain )
>>> +    {
>>> +        d->is_xenstore = 1;
>>> +        d->disable_migrate = 1;
>>> +    }
>> It only occurred to me now: Wouldn't it be worth denying the domain
>> creation request if there already is a xenstore domain?
> Hmm, the only cases where this would make sense would be:
>
> - some bug in dom0 resulting in parallel calls of init-xenstore-domain
> - an out-of-tree tool in dom0 (or another domain capable of creating
>   domains) creating a domain with the xenstore flag set
>
> I'm really not sure what would be best here. Should the hypervisor
> really be responsible for this decision?
>
> In case it is desired, I can modify the patch accordingly (the
> modification would be trivial).

For now, it might be better to knobble it in Xen to weed out bugs.

However, given future plans for restartable or multiple xenstores, I
could easily see it becoming a valid option.

~Andrew