From: Marc-André Lureau <marcandre.lureau@redhat.com>

If a display is backed by a specialized VC, allow to override the
default "vc:80Cx24C".

As suggested by Paolo, if the display doesn't implement a VC (get_vc()
returns NULL), use a fallback that will use a muxed console on stdio.

This changes the behaviour of "qemu -display none", to create a muxed
serial/monitor by default (on TTY & not daemonized).

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
---
 include/ui/console.h |  2 ++
 system/vl.c          | 27 +++++++++++++++++----------
 ui/console.c         | 14 ++++++++++++++
 3 files changed, 33 insertions(+), 10 deletions(-)

diff --git a/include/ui/console.h b/include/ui/console.h
index acb61a7f15..a4a49ffc64 100644
--- a/include/ui/console.h
+++ b/include/ui/console.h
@@ -462,12 +462,14 @@ struct QemuDisplay {
     DisplayType type;
     void (*early_init)(DisplayOptions *opts);
     void (*init)(DisplayState *ds, DisplayOptions *opts);
+    const char *vc;
 };
 
 void qemu_display_register(QemuDisplay *ui);
 bool qemu_display_find_default(DisplayOptions *opts);
 void qemu_display_early_init(DisplayOptions *opts);
 void qemu_display_init(DisplayState *ds, DisplayOptions *opts);
+const char *qemu_display_get_vc(DisplayOptions *opts);
 void qemu_display_help(void);
 
 /* vnc.c */
diff --git a/system/vl.c b/system/vl.c
index cf46e438cc..bd7fad770b 100644
--- a/system/vl.c
+++ b/system/vl.c
@@ -1372,6 +1372,7 @@ static void qemu_setup_display(void)
 static void qemu_create_default_devices(void)
 {
     MachineClass *machine_class = MACHINE_GET_CLASS(current_machine);
+    const char *vc = qemu_display_get_vc(&dpy);
 
     if (is_daemonized()) {
         /* According to documentation and historically, -nographic redirects
@@ -1390,24 +1391,30 @@ static void qemu_create_default_devices(void)
         }
     }
 
-    if (nographic) {
-        if (default_parallel)
+    if (nographic || (!vc && !is_daemonized() && isatty(STDOUT_FILENO))) {
+        if (default_parallel) {
             add_device_config(DEV_PARALLEL, "null");
+        }
         if (default_serial && default_monitor) {
             add_device_config(DEV_SERIAL, "mon:stdio");
         } else {
-            if (default_serial)
+            if (default_serial) {
                 add_device_config(DEV_SERIAL, "stdio");
-            if (default_monitor)
+            }
+            if (default_monitor) {
                 monitor_parse("stdio", "readline", false);
+            }
         }
     } else {
-        if (default_serial)
-            add_device_config(DEV_SERIAL, "vc:80Cx24C");
-        if (default_parallel)
-            add_device_config(DEV_PARALLEL, "vc:80Cx24C");
-        if (default_monitor)
-            monitor_parse("vc:80Cx24C", "readline", false);
+        if (default_serial) {
+            add_device_config(DEV_SERIAL, vc ?: "null");
+        }
+        if (default_parallel) {
+            add_device_config(DEV_PARALLEL, vc ?: "null");
+        }
+        if (default_monitor && vc) {
+            monitor_parse(vc, "readline", false);
+        }
     }
 
     if (default_net) {
diff --git a/ui/console.c b/ui/console.c
index 8ee66d10c5..a758ed62ad 100644
--- a/ui/console.c
+++ b/ui/console.c
@@ -1675,6 +1675,20 @@ void qemu_display_init(DisplayState *ds, DisplayOptions *opts)
     dpys[opts->type]->init(ds, opts);
 }
 
+const char *qemu_display_get_vc(DisplayOptions *opts)
+{
+    assert(opts->type < DISPLAY_TYPE__MAX);
+    if (opts->type == DISPLAY_TYPE_NONE) {
+        return NULL;
+    }
+    assert(dpys[opts->type] != NULL);
+    if (dpys[opts->type]->vc) {
+        return dpys[opts->type]->vc;
+    } else {
+        return "vc:80Cx24C";
+    }
+}
+
 void qemu_display_help(void)
 {
     int idx;
-- 
2.41.0