Re: [Xen-users] xen 4.4 on shared disk (NFS)

[Agustin Lopez <Agustin.Lopez@xxxxx>]

Hello Ian.

Thanks for you help.

For the first, I have not time to touch the C code. Sorry.
For the second, the wrapper, how could  work with Power off
or similar events?

Regards,
Agustin

El 22/10/2015 a las 10:57, Ian Campbell escribiÃ:
> On Wed, 2015-10-21 at 16:47 +0200, Agustin Lopez wrote:
> > Hello!
> >
> > I am using Xen 3.x and 4.1 on Debian systems over several years. All Ok
> > with 20 Domains0
> > and more of 100 DomUs.
> > I am using a lock system among several Dom0s, using xend and
> > xend-domain-lock*
> > options of the xend-config.sxp, and some patches I found in Internet.
> >
> > Now I want to upgrade to last Debian Xen release, 4,4, and new
> > tool-stack xl (or libvirt).
> > But with this upgrade my lock system can not work.
> >
> > Are there any way of lock DomUs among several Dom0s with images in a
> > shared NFS ?
> I'm afraid this previously out of tree functionality has not been
> implemented in (lib)xl, to do so would require someone to author a similar
> patch to the one you have been applying to xend but applying to the new
> toolstack instead.
>
> The new toolstack is largely written in C, if you have some familiarity
> with that and would like advice etc on how to approach implementing this
> functionality and getting it applied to the xen source then please to
> approach the xen-devel list to discuss it first. It may be that this
> usecase is better addressed in some other way (e.g. per disk image locks
> rather than whole domain locks is something worth disucssing).
>
> FWIW I don't think any particularly advanced C skills will be required, the
> tricky bit IMHO will be in the POSIX locking semantics (particularly once
> NFS is in the picture).
>
> If this https://build.opensuse.org/package/view_file/home:nick_at_seakr:xcp
> -xapi/xen/xend-domain-lock.patch (or something like it) is the patch which
> you have been using then I must say that some of the caveats in the
> comments wrt locking on an NFS share (plus my own experience with locking
> on NFS) seem rather worrying to me. If this was to be implemented in
> (lib)xl then I think we'd probably want to review the lock strategy before
> starting down the path of implementation.
>
> Otherwise, you might be able to write some sort of wrapper around xl which
> takes the necessary locks, since there is one xl process per domain (unlike
> the single process xend) so this might be workable.
>
> Ian.

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