It is possible for 'mdevctl' to output nothing, an empty string
(e.g. when no mediated devices are defined on the host). What is
weird is that when passing '--defined' then 'mdevctl' outputs an
empty JSON array instead. Nevertheless, we should accept both and
threat them the same, i.e. as no mediated devices.

Resolves: https://gitlab.com/libvirt/libvirt/-/issues/523
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
---
 src/node_device/node_device_driver.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/node_device/node_device_driver.c b/src/node_device/node_device_driver.c
index 2ef9197adc..593bc64e25 100644
--- a/src/node_device/node_device_driver.c
+++ b/src/node_device/node_device_driver.c
@@ -43,6 +43,7 @@
 #include "virutil.h"
 #include "vircommand.h"
 #include "virlog.h"
+#include "virstring.h"

 #define VIR_FROM_THIS VIR_FROM_NODEDEV

@@ -1176,6 +1177,12 @@ nodeDeviceParseMdevctlJSON(const char *jsonstring,
     size_t j;
     virJSONValue *obj;

+    if (virStringIsEmpty(jsonstring)) {
+        VIR_DEBUG("mdevctl has no defined mediated devices");
+        *devs = NULL;
+        return 0;
+    }
+
     json_devicelist = virJSONValueFromString(jsonstring);

     if (!json_devicelist || !virJSONValueIsArray(json_devicelist)) {
--
2.41.0