[PATCH-for-6.2 2/2] hw/display: Do not allow multiple identical VGA devices

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

vga_common_init() create a MemoryRegion named "vga.vram",
used as a singleton for the device class. When creating
the same device type multiple times, we get:

  $ qemu-system-mips64 -M pica61 -device isa-cirrus-vga
  RAMBlock "vga.vram" already registered, abort!
  Aborted (core dumped)

Commit 7852a77f598 ("vga: don't abort when adding a duplicate
isa-vga device") added a check for a single device, generalize
it to all VGA devices which call vga_common_init():

  $ qemu-system-mips64 -M pica61 -device isa-cirrus-vga
  qemu-system-mips64: -device isa-cirrus-vga: at most one isa-cirrus-vga device is permitted

Reported-by: John Snow <jsnow@redhat.com>
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/44
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
 hw/display/vga-isa.c |  9 ---------
 hw/display/vga.c     | 13 +++++++++++++
 2 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/hw/display/vga-isa.c b/hw/display/vga-isa.c
index 2782012196a..b930c8d2667 100644
--- a/hw/display/vga-isa.c
+++ b/hw/display/vga-isa.c
@@ -62,15 +62,6 @@ static void vga_isa_realizefn(DeviceState *dev, Error **errp)
     MemoryRegion *vga_io_memory;
     const MemoryRegionPortio *vga_ports, *vbe_ports;
 
-    /*
-     * make sure this device is not being added twice, if so
-     * exit without crashing qemu
-     */
-    if (object_resolve_path_type("", TYPE_ISA_VGA, NULL)) {
-        error_setg(errp, "at most one %s device is permitted", TYPE_ISA_VGA);
-        return;
-    }
-
     s->global_vmstate = true;
     if (!vga_common_init(s, OBJECT(dev), errp)) {
         return;
diff --git a/hw/display/vga.c b/hw/display/vga.c
index a6759c7e934..8f0d5cc9019 100644
--- a/hw/display/vga.c
+++ b/hw/display/vga.c
@@ -2172,6 +2172,19 @@ bool vga_common_init(VGACommonState *s, Object *obj, Error **errp)
 {
     int i, j, v, b;
 
+    if (obj) {
+        const char *typename = object_get_typename(obj);
+
+        /*
+         * make sure this device is not being added twice,
+         * if so exit without crashing qemu
+         */
+        if (object_resolve_path_type("", typename, NULL)) {
+            error_setg(errp, "at most one %s device is permitted", typename);
+            return false;
+        }
+    }
+
     for(i = 0;i < 256; i++) {
         v = 0;
         for(j = 0; j < 8; j++) {
-- 
2.31.1