[PATCH v3] nodedev: fix internal error when no defined mdevs 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 causes 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>
Reviewed-by: Shalini Chellathurai Saroja <shalini@xxxxxxxxxxxxx>
Reviewed-by: Martin Kletzander <mkletzan@xxxxxxxxxx>
---
 src/node_device/node_device_driver.c                | 6 ++++++
 tests/nodedevmdevctldata/mdevctl-list-empty.json    | 1 +
 tests/nodedevmdevctldata/mdevctl-list-empty.out.xml | 0
 tests/nodedevmdevctltest.c                          | 1 +
 4 files changed, 8 insertions(+)
 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 17a7aea2bb..6f8968f1f0 100644
--- a/src/node_device/node_device_driver.c
+++ b/src/node_device/node_device_driver.c
@@ -1139,6 +1139,12 @@ nodeDeviceParseMdevctlJSON(const char *jsonstring,
         goto error;
     }
 
+    if (virJSONValueArraySize(json_devicelist) == 0) {
+        VIR_DEBUG("mdevctl has no defined mediated devices");
+        *devs = NULL;
+        return 0;
+    }
+
     /* mdevctl list --dumpjson produces an output that is an array that
      * contains only a single object which contains a property for each parent
      * device */
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