Re: [libvirt] [PATCH v2] python: add virDomainGetCPUStats python binding API
On 03/16/2012 11:26 AM, Eric Blake wrote:
> +
> + if (!nparams) {
> + if ((cpu = PyDict_New()) == NULL) {
> + error = NULL;
Initialize error to NULL at the front, and you won't have to set it here.
> + goto failed;
> + }
> +
> + if (PyList_Append(ret, cpu) < 0) {
> + Py_DECREF(cpu);
> + error = NULL;
> + goto failed;
> + }
> +
> + Py_DECREF(cpu);
> + return ret;
So why are we populating the list with a single empty dictionary?
Shouldn't we instead be populating it with one empty dictionary per cpu?
That is, this code returns [{}], but if ncpus is 4, it should return
[{},{},{},{}].
In fact, instead of returning early here, you can just say:
if (nparams) {
// get parameters, via for loop over...
> + }
> + sumparams = nparams * ncpus;
> +
> + if (VIR_ALLOC_N(params, sumparams) < 0) {
> + error = PyErr_NoMemory();
> + goto failed;
> + }
> +
> + LIBVIRT_BEGIN_ALLOW_THREADS;
> + i_retval = virDomainGetCPUStats(domain, params, nparams, 0, ncpus, flags);
This will fail if ncpus > 128. You have to do this in a for loop,
grabbing only 128 cpus per iteration.
> + LIBVIRT_END_ALLOW_THREADS;
> +
> + if (i_retval < 0) {
> + error = VIR_PY_NONE;
> + goto cleanup;
> + }
} else {
i_retval = 0;
}
> +
> + for (i = 0; i < ncpus; i++) {
> + if (params[i * nparams].type == 0)
> + continue;
Technically, this is only possible if you called virDomainGetCPUStats
with ncpus larger than what the hypervisor already told you to use. But
I guess it doesn't hurt to leave these two lines in.
then drop these two lines after all (since in the i_retval==0 case,
params might be NULL and this would be a NULL deref),
> +
> + cpuparams = ¶ms[i * nparams];
This is just an address computation, so it doesn't matter if params is NULL.
> + if ((cpu = getPyVirTypedParameter(cpuparams,
nparams)) == NULL) {
Here, you want to iterate over the number of returned parameters, not
the number of array slots you passed in. s/nparams/i_retval/
and this will properly create your empty dictionary, since
getPyVirTypedParameter does the right thing if i_retval is 0. That way,
your PyList_Append() code can be reused to populate the correct return
value for ncpus regardless of whether nparams was 0.
--
Eric Blake eblake(a)redhat.com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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