[RFC: PATCH] nodeinfo: support kernels that lack socket information

[Eric Blake <eblake@xxxxxxxxxx>]

On RHEL 5, I was getting a segfault trying to start libvirtd,
because we were failing virNodeParseSocket but not checking
for errors, and then calling CPU_SET(-1, &sock_map) as a result.
But if you don't have a topology/physical_package_id file,
then you can just assume that the cpu belongs to socket 0.

* src/nodeinfo.c (virNodeGetCpuValue): Change bool into
default_value.
(virNodeParseSocket, virNodeParseNode): Update callers.
---

I'm still testing this, but wanted to get eyes on it now as I think
it belongs in 1.0.0 if it passes my testing.  Having libvirtd dump
core on RHEL 5 is not nice.  I'm not quite sure when the regression
was introduced, but it was caused by our refactoring of code to
parse different sysfs files.

 src/nodeinfo.c | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/src/nodeinfo.c b/src/nodeinfo.c
index 35c5f96..ccf0682 100644
--- a/src/nodeinfo.c
+++ b/src/nodeinfo.c
@@ -79,13 +79,14 @@ static int linuxNodeGetMemoryStats(FILE *meminfo,
                                    int *nparams);

 /* Return the positive decimal contents of the given
- * DIR/cpu%u/FILE, or -1 on error.  If MISSING_OK and the
- * file could not be found, return 1 instead of an error; this is
- * because some machines cannot hot-unplug cpu0, or because
- * hot-unplugging is disabled.  */
+ * DIR/cpu%u/FILE, or -1 on error.  If DEFAULT_VALUE is non-negative
+ * and the file could not be found, return that instead of an error;
+ * this is useful for machines that cannot hot-unplug cpu0, or where
+ * hot-unplugging is disabled, or where the kernel is too old
+ * to support NUMA cells, etc.  */
 static int
 virNodeGetCpuValue(const char *dir, unsigned int cpu, const char *file,
-                   bool missing_ok)
+                   int default_value)
 {
     char *path;
     FILE *pathfp;
@@ -100,8 +101,8 @@ virNodeGetCpuValue(const char *dir, unsigned int cpu, const char *file,

     pathfp = fopen(path, "r");
     if (pathfp == NULL) {
-        if (missing_ok && errno == ENOENT)
-            value = 1;
+        if (default_value >= 0 && errno == ENOENT)
+            value = default_value;
         else
             virReportSystemError(errno, _("cannot open %s"), path);
         goto cleanup;
@@ -174,7 +175,7 @@ static int
 virNodeParseSocket(const char *dir, unsigned int cpu)
 {
     int ret = virNodeGetCpuValue(dir, cpu, "topology/physical_package_id",
-                                 false);
+                                 0);
 # if defined(__powerpc__) || \
     defined(__powerpc64__) || \
     defined(__s390__) || \
@@ -236,7 +237,7 @@ virNodeParseNode(const char *node, int *sockets, int *cores, int *threads)
         if (sscanf(cpudirent->d_name, "cpu%u", &cpu) != 1)
             continue;

-        if ((online = virNodeGetCpuValue(node, cpu, "online", true)) < 0)
+        if ((online = virNodeGetCpuValue(node, cpu, "online", 1)) < 0)
             goto cleanup;

         if (!online)
@@ -275,7 +276,7 @@ virNodeParseNode(const char *node, int *sockets, int *cores, int *threads)
         if (sscanf(cpudirent->d_name, "cpu%u", &cpu) != 1)
             continue;

-        if ((online = virNodeGetCpuValue(node, cpu, "online", true)) < 0)
+        if ((online = virNodeGetCpuValue(node, cpu, "online", 1)) < 0)
             goto cleanup;

         if (!online)
@@ -297,7 +298,7 @@ virNodeParseNode(const char *node, int *sockets, int *cores, int *threads)
         /* logical cpu is equivalent to a core on s390 */
         core = cpu;
 # else
-        core = virNodeGetCpuValue(node, cpu, "topology/core_id", false);
+        core = virNodeGetCpuValue(node, cpu, "topology/core_id", -1);
 # endif

         CPU_SET(core, &core_maps[sock]);
-- 
1.7.11.7

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