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Re: [libvirt] [PATCH v2] python: add virDomainGetCPUStats python binding API



On 03/17/2012 01:26 AM, Eric Blake wrote:
On 03/14/2012 07:03 AM, Guannan Ren wrote:
     dom.getCPUStats(True, 0)
       [{'cpu_time': 92913537401L, 'system_time': 5470000000L, 'user_time': 310000000L}]

     dom.getCPUStats(False, 0)
       [{'cpu_time': 39476858499L}, {'cpu_time': 10627048370L}, {'cpu_time': 21270945682L}, {'cpu_time': 21556420641L}]

     *generator.py Add a new naming rule
     *libvirt-override-api.xml The API function description
     *libvirt-override.c Implement it.
---
  python/generator.py             |    5 +-
  python/libvirt-override-api.xml |   10 +++
  python/libvirt-override.c       |  164 +++++++++++++++++++++++++++++++++++++++
  3 files changed, 178 insertions(+), 1 deletions(-)

+++ b/python/libvirt-override-api.xml
@@ -149,6 +149,16 @@
        <arg name='path' type='char *' info='the path for the block device'/>
        <arg name='flags' type='int' info='flags (unused; pass 0)'/>
      </function>
+<function name='virDomainGetCPUStats' file='python'>
+<info>Extracts CPU statistics for a running domain, On success it will return a list of data of dictionary type.
s/, On/. On/

Long lines; can you wrap this to fit in 80 columns?

+   If boolean total is True, the first element of the list refers to CPU0 on the host, second element is CPU1, and so on.
s/total is True/total is False/

+   The format of data struct is like [{cpu_time:xxx},{cpu_time:xxx}, ...]
+   If it is False, it returns total domain CPU statistics like [{cpu_time:xxx, user_time:xxx, system_time:xxx}]</info>
s/False/True/

+
+    if (!PyBool_Check(totalbool)) {
+        PyErr_Format(PyExc_TypeError,
+                    "The \"total\" attribute must be bool");
+        return NULL;
+    }
+
+    if ((ret = PyList_New(0)) == NULL)
+        return NULL;
+
+    if (totalbool == Py_False) {
Per other code in libvirt-override.c, you can't compare totalbool (type
PyObject) with Py_False, at least not on all compilers.  You need
something like this instead:

             /* Hack - Python's definition of Py_True breaks strict
              * aliasing rules, so can't directly compare
              */
             if (PyBool_Check(value)) {
                 PyObject *hacktrue = PyBool_FromLong(1);
                 temp->value.b = hacktrue == value ? 1 : 0;
                 Py_DECREF(hacktrue);

Yes, it did report warning in compiling as follows due to the case from PyIntObject* to PyObject* warning :dereferencing type-punned pointer might break strict-aliasing rules [-Wstrict-aliasing]

     GCC command line to reproduce the error:
     gcc -Wstrict-aliasing=1 -O2 cpythonexample.c

Actually PyObject_IsTrue() is a more light-weight approach to do the checking instead of creating a intermediate PyObject * for the compare. But for the more portability, It is still better to
     choose the above comparing approach for boolean value.

     Guannan Ren


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