vl: add -vga help support

Provide help output similar to other argument help handling:

$ qemu-system-x86_64 -vga help
none
std                  standard VGA (default)
cirrus               Cirrus VGA
vmware               VMWare SVGA
xenfb
qxl                  QXL VGA
virtio               Virtio VG

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20190412152713.16018-3-marcandre.lureau@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

1 files changed, 31 insertions, 9 deletions

diff --git a/vl.c b/vl.c
index 6b2820483c..b6709514c1 100644
--- a/vl.c
+++ b/vl.c
@@ -2069,11 +2069,39 @@ static bool vga_interface_available(VGAInterfaceType t)
            object_class_by_name(ti->class_names[1]);
 }
 
-static void select_vgahw(const char *p)
+static const char *
+get_default_vga_model(const MachineClass *machine_class)
+{
+    if (machine_class->default_display) {
+        return machine_class->default_display;
+    } else if (vga_interface_available(VGA_CIRRUS)) {
+        return "cirrus";
+    } else if (vga_interface_available(VGA_STD)) {
+        return "std";
+    }
+
+    return NULL;
+}
+
+static void select_vgahw(const MachineClass *machine_class, const char *p)
 {
     const char *opts;
     int t;
 
+    if (g_str_equal(p, "help")) {
+        const char *def = get_default_vga_model(machine_class);
+
+        for (t = 0; t < VGA_TYPE_MAX; t++) {
+            const VGAInterfaceInfo *ti = &vga_interfaces[t];
+
+            if (vga_interface_available(t) && ti->opt_name) {
+                printf("%-20s %s%s\n", ti->opt_name, ti->name ?: "",
+                       g_str_equal(ti->opt_name, def) ? " (default)" : "");
+            }
+        }
+        exit(0);
+    }
+
     assert(vga_interface_type == VGA_NONE);
     for (t = 0; t < VGA_TYPE_MAX; t++) {
         const VGAInterfaceInfo *ti = &vga_interfaces[t];
@@ -4424,16 +4452,10 @@ int main(int argc, char **argv, char **envp)
 
     /* If no default VGA is requested, the default is "none".  */
     if (default_vga) {
-        if (machine_class->default_display) {
-            vga_model = machine_class->default_display;
-        } else if (vga_interface_available(VGA_CIRRUS)) {
-            vga_model = "cirrus";
-        } else if (vga_interface_available(VGA_STD)) {
-            vga_model = "std";
-        }
+        vga_model = get_default_vga_model(machine_class);
     }
     if (vga_model) {
-        select_vgahw(vga_model);
+        select_vgahw(machine_class, vga_model);
     }
 
     if (watchdog) {