Re: [PATCH v4 5/8] qemu_monitor: implement query-cpu-model-comparison

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On 7/24/19 12:18 PM, Boris Fiuczynski wrote:
On 7/17/19 4:03 PM, Collin Walling wrote:

[...]

diff --git a/src/qemu/qemu_monitor_json.c b/src/qemu/qemu_monitor_json.c
index b599ee6..3c33c63 100644
--- a/src/qemu/qemu_monitor_json.c
+++ b/src/qemu/qemu_monitor_json.c
@@ -5875,6 +5875,101 @@ qemuMonitorJSONGetCPUModelBaseline(qemuMonitorPtr mon,
  }
+static int
+qemuMonitorJSONParseCPUModelPropName(size_t pos ATTRIBUTE_UNUSED,
+                                     virJSONValuePtr item,
+                                     void *opaque)
+{
+    if (!qemuMonitorJSONParseCPUModelProperty(virJSONValueGetString(item),
+                                              item, opaque))

This need to be changed into

     if (qemuMonitorJSONParseCPUModelProperty(virJSONValueGetString(item),
                                              item, opaque) < 0)


Yes, thank you for catching this one.

+        return -1;
+
+    virJSONValueFree(item);
+    return 0;
+}
+
+
+int
+qemuMonitorJSONGetCPUModelComparison(qemuMonitorPtr mon,
+                                     const char *model_a_name,
+                                     int model_a_nprops,
+                                     virCPUFeatureDefPtr model_a_props,
+                                     const char *model_b_name,
+                                     int model_b_nprops,
+                                     virCPUFeatureDefPtr model_b_props,
+                                     qemuMonitorCPUModelInfoPtr *model_result)
+{
+    int ret = -1;
+    virJSONValuePtr model_a;
+    virJSONValuePtr model_b = NULL;
+    virJSONValuePtr cmd = NULL;
+    virJSONValuePtr reply = NULL;
+    virJSONValuePtr data;
+    const char *result_name;
+    virJSONValuePtr props;
+    qemuMonitorCPUModelInfoPtr compare = NULL;
+
+    if (!(model_a = qemuMonitorJSONMakeCPUModel(model_a_name, model_a_nprops,
+                                                model_a_props, true)) ||
+        !(model_b = qemuMonitorJSONMakeCPUModel(model_b_name, model_b_nprops,
+                                                model_b_props, true)))
+        goto cleanup;
+
+    if (!(cmd = qemuMonitorJSONMakeCommand("query-cpu-model-comparison",
+                                           "a:modela", &model_a,
+                                           "a:modelb", &model_b,
+                                           NULL)))
+        goto cleanup;
+
+    if (qemuMonitorJSONCommand(mon, cmd, &reply) < 0)
+        goto cleanup;
+
+    if (qemuMonitorJSONCheckError(cmd, reply) < 0)

Did you test scenarios which contain unknown cpu model name or unknown features?
This caused errors for me during testing that resulted in e.g.
 error : qemuMonitorJSONCheckError:415 : internal error: unable to execute QEMU command 'query-cpu-model-comparison': Property '.boris' not found  warning : virQEMUCapsLogProbeFailure:4586 : Failed to probe capabilities for /usr/bin/qemu-system-s390x: internal error: unable to execute QEMU command 'query-cpu-model-comparison': Property '.boris' not found

If I think about a scenario like: I run "virsh domcapabilties" on a new machine with new cpu model and new cpu features, new libvirt, new qemu and use "virsh hypervisor-cpu-compare" with the output xml on my old machine with old cpu &feature, older libvirt and older qemu
I would expect to get as an answer: Incompatible

If my expectation to get incompatible is wrong please correct me but an "internal error" is not what should occur.
What is the qemu specification for this?



Two routes:

1) Fix up the logic in virQEMUCapsCPUModelComparison

Please see my comments on patch 8.

2) Change the error class in the QEMU QMP code

The QMP code in QEMU currently reports a "GenericError" whenever
something goes wrong (such as an unknown CPU model or feature). A
possible solution to this would be to alter that code to set a specific
error class, have libvirt check for that specific error type in the
JSON, then handle it appropriately to print a cleaner message.

There is one drawback: we would technically be reporting this error
twice -- once in virsh, and another in the libvirt daemon (the internal
error) unless we wanted to suppress it.

This is one solution without too much messy code.

+        goto cleanup;
+
+    data = virJSONValueObjectGetObject(reply, "return");
+
+    if (!(result_name = virJSONValueObjectGetString(data, "result"))) {
+        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                       _("query-cpu-model-comparison reply data was missing "
+                         "'result'"));
+        goto cleanup;
+    }
+
+    if (!(props = virJSONValueObjectGetArray(data, "responsible-properties"))) {
+        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                       _("query-cpu-model-comparison reply data was missing "
+                         "'responsible-properties'"));
+        goto cleanup;
+    }
+
+    if (VIR_ALLOC(compare) < 0)
+        goto cleanup;
+
+    if (VIR_STRDUP(compare->name, result_name) < 0)
+        goto cleanup;
+
+    if (VIR_ALLOC_N(compare->props, virJSONValueArraySize(props)) < 0)
+        goto cleanup;
+
+    if (virJSONValueArrayForeachSteal(props,
+ qemuMonitorJSONParseCPUModelPropName,
+                                      compare) < 0)
+        goto cleanup;
+
+    VIR_STEAL_PTR(*model_result, compare);
+    ret = 0;
+
+ cleanup:
+    qemuMonitorCPUModelInfoFree(compare);
+    virJSONValueFree(cmd);
+    virJSONValueFree(reply);
+    virJSONValueFree(model_a);
+    virJSONValueFree(model_b);
+    return ret;
+}
+
+

[...]

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