udevListInterfacesByStatus: Don't try to return NULL names

In case when the interface is being detached/reattached it may happen
that udev will return NULL from 'udev_device_get_sysname()'.

As the RPC code requires nonnull strings in the return array it fails to
serialize such reply:

 libvirt: XML-RPC error : Unable to encode message payload

Fix this by simply ignoring such interfaces as there's nothing we can
report in such case.

A similar fix was done to 'udevConnectListAllInterfaces' in commit
2ca94317ac.

Resolves: https://issues.redhat.com/browse/RHEL-34615
Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

src/interface/interface_backend_udev.c

@@ -137,55 +137,21 @@ udevGetDevices(struct udev *udev, virUdevStatus status)
     return enumerate;
 }
 
-static int
-udevNumOfInterfacesByStatus(virConnectPtr conn, virUdevStatus status,
-                            virInterfaceObjListFilter filter)
-{
-    struct udev *udev = udev_ref(driver->udev);
-    struct udev_enumerate *enumerate = NULL;
-    struct udev_list_entry *devices;
-    struct udev_list_entry *dev_entry;
-    int count = 0;
-
-    enumerate = udevGetDevices(udev, status);
-
-    if (!enumerate) {
-        virReportError(VIR_ERR_INTERNAL_ERROR,
-                       _("failed to get number of %1$s interfaces on host"),
-                       virUdevStatusString(status));
-        count = -1;
-        goto cleanup;
-    }
-
-    /* Do the scan to load up the enumeration */
-    udev_enumerate_scan_devices(enumerate);
-
-    /* Get a list we can walk */
-    devices = udev_enumerate_get_list_entry(enumerate);
-
-    /* For each item so we can count */
-    udev_list_entry_foreach(dev_entry, devices) {
-        struct udev_device *dev;
-        const char *path;
-        g_autoptr(virInterfaceDef) def = NULL;
-
-        path = udev_list_entry_get_name(dev_entry);
-        dev = udev_device_new_from_syspath(udev, path);
-
-        def = udevGetMinimalDefForDevice(dev);
-        if (filter(conn, def))
-            count++;
-        udev_device_unref(dev);
-    }
-
- cleanup:
-    if (enumerate)
-        udev_enumerate_unref(enumerate);
-    udev_unref(udev);
-
-    return count;
-}
 
+/**
+ * udevListInterfacesByStatus:
+ *
+ * @conn: connection object
+ * @names: optional pointer to array to be filled with interface names
+ * @names_len: size of @names
+ * @status: status of interfaces to be listed
+ * @filter: ACL filter function
+ *
+ * Lists interfaces with status matching @status filling them into @names (if
+ * non-NULL) and returns the number of such interfaces.
+ *
+ * In case of an error -1 is returned and no interfaces are filled into @names.
+ */
 static int
 udevListInterfacesByStatus(virConnectPtr conn,
                            char **const names,
@@ -219,18 +185,27 @@ udevListInterfacesByStatus(virConnectPtr conn,
     udev_list_entry_foreach(dev_entry, devices) {
         struct udev_device *dev;
         const char *path;
+        const char *name;
         g_autoptr(virInterfaceDef) def = NULL;
 
         /* Ensure we won't exceed the size of our array */
-        if (count >= names_len)
+        if (names && count >= names_len)
             break;
 
         path = udev_list_entry_get_name(dev_entry);
         dev = udev_device_new_from_syspath(udev, path);
 
+        if (!(name = udev_device_get_sysname(dev))) {
+            /* Name can be NULL in case when the interface is being unbound
+             * from the driver. The list API requires names to be present */
+            VIR_DEBUG("Skipping interface '%s', name == NULL", path);
+            continue;
+        }
+
         def = udevGetMinimalDefForDevice(dev);
         if (filter(conn, def)) {
-            names[count] = g_strdup(udev_device_get_sysname(dev));
+            if (names)
+                names[count] = g_strdup(name);
             count++;
         }
         udev_device_unref(dev);
@@ -242,14 +217,15 @@ udevListInterfacesByStatus(virConnectPtr conn,
     return count;
 }
 
+
 static int
 udevConnectNumOfInterfaces(virConnectPtr conn)
 {
     if (virConnectNumOfInterfacesEnsureACL(conn) < 0)
         return -1;
 
-    return udevNumOfInterfacesByStatus(conn, VIR_UDEV_IFACE_ACTIVE,
-                                       virConnectNumOfInterfacesCheckACL);
+    return udevListInterfacesByStatus(conn, NULL, 0, VIR_UDEV_IFACE_ACTIVE,
+                                      virConnectNumOfInterfacesCheckACL);
 }
 
 static int
@@ -271,8 +247,8 @@ udevConnectNumOfDefinedInterfaces(virConnectPtr conn)
     if (virConnectNumOfDefinedInterfacesEnsureACL(conn) < 0)
         return -1;
 
-    return udevNumOfInterfacesByStatus(conn, VIR_UDEV_IFACE_INACTIVE,
-                                       virConnectNumOfDefinedInterfacesCheckACL);
+    return udevListInterfacesByStatus(conn, NULL, 0, VIR_UDEV_IFACE_INACTIVE,
+                                      virConnectNumOfDefinedInterfacesCheckACL);
 }
 
 static int