Re: [Xen-devel] [PATCH 3/3] libxl: update vcpus bitmap in retrieved guest config

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On Tue, 2016-06-07 at 17:03 +0100, Wei Liu wrote:
> On Tue, Jun 07, 2016 at 03:45:29PM +0100, Anthony PERARD wrote:
> > 
> > > --- a/tools/libxl/libxl.c
> > > +++ b/tools/libxl/libxl.c
> > > @@ -7222,6 +7222,57 @@ void libxl_mac_copy(libxl_ctx *ctx,
> > > libxl_mac *dst, libxl_mac *src)
> > >          (*dst)[i] = (*src)[i];
> > >  }
> > >  
> > > +static int libxl__update_avail_vcpus_qmp(libxl__gc *gc, uint32_t
> > > domid,
> > > +                                         unsigned int max_vcpus,
> > > +                                         libxl_bitmap *map)
> > > +{
> > > +    unsigned int count, i;
> > > +    int rc;
> > > +
> > > +    /* For QEMU upstream we always need to return the number
> > > +     * of cpus present to QEMU whether they are online or not;
> > > +     * otherwise QEMU won't accept the saved state.
> > > +     */
> > > +    rc = libxl__qmp_query_cpus(gc, domid, &count);
> > > +    if (rc) {
> > > +        LOG(ERROR, "fail to get number of cpus for domain %d",
> > > domid);
> > > +        goto out;
> > > +    }
> > > +
> > > +    for (i = 0; i < count; i++)
> > > +        libxl_bitmap_set(map, i);
> > What if I have cpu 1, 7 and 42 online, but all the other offline?
> > 
> I have more or less the same question when I wrote this patch. At
> that
> time I thought the avail_vcpus was only used for generating -smp
> option
> to QEMU.
> 
> In your example, you will have -smp 3,maxvcpus=$Y. I think the
> migration
> should still succeed. Furthermore, the cpu-add operation doesn't
> care,
> so it probably won't have visible effect.
> 
> I agree it would be good to set the exact bits though -- if you can
> tell
> me which field to test. 
> 
Perhaps at least mention something about all this either in a comment
or in the changelog?

Regards,
Dario
-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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