hw/display: Restrict virtio-gpu-udmabuf stubs to !Linux

When using qemu configured with --enabled-modules, the
generic stubs are used instead of the module symbols:

  qemu-system-x86_64: -device virtio-vga,blob=on: cannot enable blob resources without udmabuf

Restrict the stubs to Linux and only link them when
CONFIG_VIRTIO_GPU is disabled (only the modularized
version is available when it is enabled).

Reported-by: Maxim R. <mrom06@ya.ru>
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/553
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20210823100454.615816-2-philmd@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

hw/display/meson.build

@@ -56,7 +56,8 @@ if config_all_devices.has_key('CONFIG_VIRTIO_GPU')
   virtio_gpu_ss = ss.source_set()
   virtio_gpu_ss.add(when: 'CONFIG_VIRTIO_GPU',
                     if_true: [files('virtio-gpu-base.c', 'virtio-gpu.c'), pixman])
-  virtio_gpu_ss.add(when: 'CONFIG_LINUX', if_true: files('virtio-gpu-udmabuf.c'))
+  virtio_gpu_ss.add(when: 'CONFIG_LINUX', if_true: files('virtio-gpu-udmabuf.c'),
+                                          if_false: files('virtio-gpu-udmabuf-stubs.c'))
   virtio_gpu_ss.add(when: 'CONFIG_VHOST_USER_GPU', if_true: files('vhost-user-gpu.c'))
   hw_display_modules += {'virtio-gpu': virtio_gpu_ss}
 

stubs/meson.build

@@ -52,7 +52,6 @@ if have_system
   stub_ss.add(files('semihost.c'))
   stub_ss.add(files('usb-dev-stub.c'))
   stub_ss.add(files('xen-hw-stub.c'))
-  stub_ss.add(files('virtio-gpu-udmabuf.c'))
 else
   stub_ss.add(files('qdev.c'))
 endif