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Re: [Libvir] PATCH: Fix compat for Xen 3.2.0



On Sat, Jan 19, 2008 at 09:21:07PM +0100, Jim Meyering wrote:
> "Daniel P. Berrange" <berrange redhat com> wrote:
> 
> > Xen 3.2.0 removed the sockets_per_node field from the nodeinfo data returned
> > by XenD. I previously add compat for this, but got it in the wrong place
> > so it would most likely end up in a divide-by-zero error. This patch
> > re-arranges it to be correct.
> >
> > diff -rup libvirt-0.4.0.orig/src/xend_internal.c libvirt-0.4.0.new/src/xend_internal.c
> > --- libvirt-0.4.0.orig/src/xend_internal.c	2007-12-17 18:05:27.000000000 -0500
> > +++ libvirt-0.4.0.new/src/xend_internal.c	2008-01-18 21:13:30.000000000 -0500
> > @@ -1907,6 +1907,9 @@ sexpr_to_xend_node_info(struct sexpr *ro
> >      info->mhz = sexpr_int(root, "node/cpu_mhz");
> >      info->nodes = sexpr_int(root, "node/nr_nodes");
> >      info->sockets = sexpr_int(root, "node/sockets_per_node");
> > +    info->cores = sexpr_int(root, "node/cores_per_socket");
> > +    info->threads = sexpr_int(root, "node/threads_per_core");
> > +
> >      /* Xen 3.2.0 replaces sockets_per_node with 'nr_cpus'.
> >       * Old Xen calculated sockets_per_node using its internal
> >       * nr_cpus / (nodes*cores*threads), so fake it ourselves
> > @@ -1921,8 +1924,6 @@ sexpr_to_xend_node_info(struct sexpr *ro
> >          if (info->sockets == 0)
> >              info->sockets = 1;
> >      }
> > -    info->cores = sexpr_int(root, "node/cores_per_socket");
> > -    info->threads = sexpr_int(root, "node/threads_per_core");
> >      return (0);
> >  }
> 
> ACK.
> 
> Now that you mention divide-by-zero,
> is there something that guarantees none of the
> terms in the denominator there is zero?
> 
>         info->sockets = nr_cpus / (info->nodes * info->cores * info->threads);

You always have at least 1 numa node, at least 1 core, and at least 1
hyperthread, so you'd only get a zero in those if there was a bug in the
Xen hypervisor

Regards,
Dan.
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