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



Daniel P. Berrange wrote:
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

.. And that would never happen :-)

Rich.

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