If device->active_dlt = -1, show "Unknown" rather than "DLT -1".

It means we don't know the active link-layer header type - probably
because the device can't be opened, so we can't get the default linktype
or the list of available linktypes - so show it as "Unknown".

Bug: 14847
Change-Id: I5a1ad360d2ae461e8db57e387679700a566b0949
Reviewed-on: https://code.wireshark.org/review/28185
Reviewed-by: Guy Harris <guy@alum.mit.edu>

2 files changed, 27 insertions, 13 deletions

diff --git a/ui/qt/capture_interfaces_dialog.cpp b/ui/qt/capture_interfaces_dialog.cpp
index 5f705465cc..b5d8df20b5 100644
--- a/ui/qt/capture_interfaces_dialog.cpp
+++ b/ui/qt/capture_interfaces_dialog.cpp
@@ -109,13 +109,19 @@ public:
 
         QString default_str = QObject::tr("default");
 
-        QString linkname = QObject::tr("DLT %1").arg(device->active_dlt);
-        for (GList *list = device->links; list != NULL; list = g_list_next(list)) {
-            link_row *linkr = (link_row*)(list->data);
-            // XXX ...and if they're both -1?
-            if (linkr->dlt == device->active_dlt) {
-                linkname = linkr->name;
-                break;
+        // XXX - this is duplicated in InterfaceTreeModel::data;
+        // it should be done in common code somewhere.
+        QString linkname;
+        if (device->active_dlt == -1)
+            linkname = "Unknown";
+        else {
+            linkname = QObject::tr("DLT %1").arg(device->active_dlt);
+            for (GList *list = device->links; list != NULL; list = g_list_next(list)) {
+                link_row *linkr = (link_row*)(list->data);
+                if (linkr->dlt == device->active_dlt) {
+                    linkname = linkr->name;
+                    break;
+                }
             }
         }
         setText(col_link_, linkname);
diff --git a/ui/qt/models/interface_tree_model.cpp b/ui/qt/models/interface_tree_model.cpp
index 2dea30ff4e..d2b7217284 100644
--- a/ui/qt/models/interface_tree_model.cpp
+++ b/ui/qt/models/interface_tree_model.cpp
@@ -158,12 +158,20 @@ QVariant InterfaceTreeModel::data(const QModelIndex &index, int role) const
             }
             else if ( col == IFTREE_COL_DLT )
             {
-                QString linkname = QObject::tr("DLT %1").arg(device->active_dlt);
-                for (GList *list = device->links; list != NULL; list = g_list_next(list)) {
-                    link_row *linkr = (link_row*)(list->data);
-                    if (linkr->dlt != -1 && linkr->dlt == device->active_dlt) {
-                        linkname = linkr->name;
-                        break;
+                // XXX - this is duplicated in
+                // InterfaceTreeWidgetItem::updateInterfaceColumns;
+                // it should be done in common code somewhere.
+                QString linkname;
+                if (device->active_dlt == -1)
+                    linkname = "Unknown";
+                else {
+                    linkname = QObject::tr("DLT %1").arg(device->active_dlt);
+                    for (GList *list = device->links; list != NULL; list = g_list_next(list)) {
+                        link_row *linkr = (link_row*)(list->data);
+                        if (linkr->dlt == device->active_dlt) {
+                            linkname = linkr->name;
+                            break;
+                        }
                     }
                 }