[PATCH] nodedev: fix error when no defined mdev exist

[Boris Fiuczynski <fiuczy@xxxxxxxxxxxxx>]

Commit e9b534905f4 introduced an error when parsing an empty list
returned from mdevctl.

This occurs e.g. if nodedev-undefine is used to undefine the last
defined mdev which cuases the following error messages

 libvirtd[33143]: internal error: Unexpected format for mdevctl response
 libvirtd[33143]: internal error: failed to query mdevs from mdevctl:
 libvirtd[33143]: mdevctl failed to updated mediated devices

Signed-off-by: Boris Fiuczynski <fiuczy@xxxxxxxxxxxxx>
---
 src/node_device/node_device_driver.c          | 68 ++++++++++---------
 .../mdevctl-list-empty.json                   |  1 +
 .../mdevctl-list-empty.out.xml                |  0
 tests/nodedevmdevctltest.c                    |  1 +
 4 files changed, 37 insertions(+), 33 deletions(-)
 create mode 100644 tests/nodedevmdevctldata/mdevctl-list-empty.json
 create mode 100644 tests/nodedevmdevctldata/mdevctl-list-empty.out.xml

diff --git a/src/node_device/node_device_driver.c b/src/node_device/node_device_driver.c
index b4dd57e5f4..31525f2312 100644
--- a/src/node_device/node_device_driver.c
+++ b/src/node_device/node_device_driver.c
@@ -1123,51 +1123,53 @@ nodeDeviceParseMdevctlJSON(const char *jsonstring,
     /* mdevctl list --dumpjson produces an output that is an array that
      * contains only a single object which contains a property for each parent
      * device */
-    if (virJSONValueArraySize(json_devicelist) != 1) {
-        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
-                       _("Unexpected format for mdevctl response"));
-        goto error;
-    }
-
-    obj = virJSONValueArrayGet(json_devicelist, 0);
-
-    if (!virJSONValueIsObject(obj)) {
-        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
-                       _("device list is not an object"));
-        goto error;
-    }
-
-    n = virJSONValueObjectKeysNumber(obj);
-    for (i = 0; i < n; i++) {
-        const char *parent;
-        virJSONValue *child_array;
-        int nchildren;
+    if (virJSONValueArraySize(json_devicelist) > 0) {
+        if (virJSONValueArraySize(json_devicelist) != 1) {
+            virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                           _("Unexpected format for mdevctl response"));
+            goto error;
+        }
 
-        /* The key of each object property is the name of a parent device
-         * which maps to an array of child devices */
-        parent = virJSONValueObjectGetKey(obj, i);
-        child_array = virJSONValueObjectGetValue(obj, i);
+        obj = virJSONValueArrayGet(json_devicelist, 0);
 
-        if (!virJSONValueIsArray(child_array)) {
+        if (!virJSONValueIsObject(obj)) {
             virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
-                           _("Parent device's JSON object data is not an array"));
+                           _("device list is not an object"));
             goto error;
         }
 
-        nchildren = virJSONValueArraySize(child_array);
+        n = virJSONValueObjectKeysNumber(obj);
+        for (i = 0; i < n; i++) {
+            const char *parent;
+            virJSONValue *child_array;
+            int nchildren;
 
-        for (j = 0; j < nchildren; j++) {
-            g_autoptr(virNodeDeviceDef) child = NULL;
-            virJSONValue *child_obj = virJSONValueArrayGet(child_array, j);
+            /* The key of each object property is the name of a parent device
+             * which maps to an array of child devices */
+            parent = virJSONValueObjectGetKey(obj, i);
+            child_array = virJSONValueObjectGetValue(obj, i);
 
-            if (!(child = nodeDeviceParseMdevctlChildDevice(parent, child_obj))) {
+            if (!virJSONValueIsArray(child_array)) {
                 virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
-                               _("Unable to parse child device"));
+                               _("Parent device's JSON object data is not an array"));
                 goto error;
             }
 
-            if (VIR_APPEND_ELEMENT(outdevs, noutdevs, child) < 0)
-                goto error;
+            nchildren = virJSONValueArraySize(child_array);
+
+            for (j = 0; j < nchildren; j++) {
+                g_autoptr(virNodeDeviceDef) child = NULL;
+                virJSONValue *child_obj = virJSONValueArrayGet(child_array, j);
+
+                if (!(child = nodeDeviceParseMdevctlChildDevice(parent, child_obj))) {
+                    virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                                   _("Unable to parse child device"));
+                    goto error;
+                }
+
+                if (VIR_APPEND_ELEMENT(outdevs, noutdevs, child) < 0)
+                    goto error;
+            }
         }
     }
 
diff --git a/tests/nodedevmdevctldata/mdevctl-list-empty.json b/tests/nodedevmdevctldata/mdevctl-list-empty.json
new file mode 100644
index 0000000000..fe51488c70
--- /dev/null
+++ b/tests/nodedevmdevctldata/mdevctl-list-empty.json
@@ -0,0 +1 @@
+[]
diff --git a/tests/nodedevmdevctldata/mdevctl-list-empty.out.xml b/tests/nodedevmdevctldata/mdevctl-list-empty.out.xml
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/tests/nodedevmdevctltest.c b/tests/nodedevmdevctltest.c
index 8ba1d2da70..e246de4d87 100644
--- a/tests/nodedevmdevctltest.c
+++ b/tests/nodedevmdevctltest.c
@@ -360,6 +360,7 @@ mymain(void)
 
     DO_TEST_LIST_DEFINED();
 
+    DO_TEST_PARSE_JSON("mdevctl-list-empty");
     DO_TEST_PARSE_JSON("mdevctl-list-multiple");
 
     DO_TEST_DEFINE("mdev_d069d019_36ea_4111_8f0a_8c9a70e21366");
-- 
2.31.1