Re: [Xen-devel] [PATCH] tools: add closure to xc_domain_save switch_qemu_logdirty callback

[Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>]

On Wed, 2010-10-13 at 18:12 +0100, Brendan Cully wrote:
> On Wednesday, 13 October 2010 at 17:51, Ian Campbell wrote:
> > On Wed, 2010-10-13 at 17:37 +0100, Brendan Cully wrote:
> > > On Wednesday, 13 October 2010 at 13:46, Ian Campbell wrote:
> > > I could make the python bindings patch if you'd like (or you're
> > > welcome to :). Just let me know when the changes have hit the tree.
> > 
> > I took a look but I think I'd only end up breaking something, would you
> > mind?
> 
> sure, when it hits the tree. It looks like your changes will work with
> the existing code until then.

thanks.

> > One issue which was immediately apparent on my quick glance is that the
> > callback returns void but the switch_qemu_logdirty in libcheckpoint.c
> > can fail. Do you think we need to propagate an error code or can that
> > switch_qemu_logdirty be made to not fail (or safely ignore failure)? I
> > suspect libxl's error handling in this area could be improved if there
> > was error propagation here.
> 
> Since switch_qemu_logdirty runs through xenstore and depends on a
> remote response, I don't think it can be guaranteed not to
> fail, or to fail safely (if the remote hasn't turned on logdirty,
> checkpointing is broken). So ideally we'd propagate the error.

I'll update the patch to do so and repost.

> Honestly, I'm not even sure why this is a callback, except that it's
> an easy way to reuse an existing xenstore handle. Shouldn't
> xc_domain_save just handle this internally, like it does for non-QEMU
> logdirty? Maybe that's a job for another day :)

libxenctrl doesn't link against libxenstore so it can't do it itself.

Ian.


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