RE: [Xen-devel] xenstore -- read UUID

[dinesh chandrasekaran <dinesh_chan8@xxxxxxxxxxx>]

Hi geoffrey,
                the xen_domain_handle_t in the domain handle field is an unsigned char array of size 16.
Where could the UUID be accessed from?
or how would you relate the d->handle to the domain's uuid (where d is of type struct domain *d).
is all the 16 entries in the d->handle clubbed together to get the domain's uuid?

thanks,
Dinesh C

> Date: Wed, 10 Sep 2008 08:31:11 -0700
> From: geoffrey@xxxxxxxxx
> To: Derek.Murray@xxxxxxxxxxxx
> Subject: Re: [Xen-devel] xenstore -- read UUID
> CC: dinesh_chan8@xxxxxxxxxxx; xen-devel@xxxxxxxxxxxxxxxxxxx; xen-users@xxxxxxxxxxxxxxxxxxx
>
> Hi everyone,
>
> Sorry for the late joining to this thread.
>
> If you really want to gather a domain's uuid from within the
> hypervisor, it's actually possible to do without xenstore.
> A domain's uuid gets stored as a xen_domain_handle_t in the domain
> handle field (see xen/include/xen/sched.h and xen/commom/domctl.c).
> The uuid of a domain gets passed to xen on domain creation. The uuid
> can also be read from a privileged domain by issuing the
> XEN_DOMCTL_getdomaininfo hypercall.
>
> But as Derek mentioned earlier, you can read the domain uuid from a
> guest via xenstore which is probably a better idea.
>
> cheers,
>
> geoffrey
>
> On Wed, Sep 10, 2008 at 4:49 AM, Derek Murray <Derek.Murray@xxxxxxxxxxxx> wrote:
> > Hi Dinesh,
> >
> > On Wed, Sep 10, 2008 at 1:24 AM, dinesh chandrasekaran
> > <dinesh_chan8@xxxxxxxxxxx> wrote:
> >> they were 2 seperate questions... sorry for the typos...
> >> How to access xenstore from Dom-0? -- which you said 'YES'...
> >
> > Yes, this is certainly possible: your code should work (I haven't
> > tested it) in Dom0 user-space. For another example, see
> > tools/xenstore/xsls.c, which implements ls functionality for xenstore
> > using the same interface.
> >
> >> And How to access xenstore from hypervosor?
> >
> > There is no code to do this in Xen at the moment.
> >
> >> If the hypervisor has no knowledge about XenStore, Dom-0 must have the full
> >> control over the xenstore.
> >
> > Correct. XenStore is simply implemented as a user-space daemon
> > (xenstored), running as root in Dom0.
> >
> >> I need to build a table with some fields one of which should never change
> >> during a VMs lifetime.
> >> For example, if I chose the domain_id whose value is transient, If the VM
> >> reboots, its domain_id changes.
> >> That is the reason why I opted for the UUID of a domain that persists over
> >> time even after migration to another machine.
> >> The only way I could get a domain's UUID is through the xenstore and want to
> >> take away domain-0 from the picture, which
> >> according to you is almost impossible.
> >
> > Instead of Dom0, you could possibly do this in a stubdomain. It is
> > possible to access XenStore from a MiniOS-based domain.
> >
> > Regards,
> >
> > Derek Murray.
> >
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxxxxxxxx
> > http://lists.xensource.com/xen-devel
> >

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