Re: [PATCH v3] Warn user if the vga flag is passed but no vga device is created

[Peter Maydell]

On Fri, 6 May 2022 at 16:43, Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> On 5/6/22 16:48, Peter Maydell wrote:
> >> I'm just in progress of preparing a pull request with misc patches, I can
> >> also throw it in there if nobody minds.
> > Paolo mentioned on IRC yesterday that there was some detail he thought
> > it wasn't handling right with VGA_DEVICE, but I didn't really understand
> > the details. Paolo ?
>
> Yeah, I was wondering if this would warn for "-device VGA".  But if so
> it should be enough to do this to fix it:
>
> diff --git a/softmmu/vl.c b/softmmu/vl.c
> index eef1558281..7ff76b795a 100644
> --- a/softmmu/vl.c
> +++ b/softmmu/vl.c
> @@ -1352,6 +1352,7 @@ static void qemu_disable_default_devices(void)
>
>       if (!vga_model && !default_vga) {
>           vga_interface_type = VGA_DEVICE;
> +        vga_interface_created = true;
>       }
>       if (!has_defaults || machine_class->no_serial) {
>           default_serial = 0;

Can you explain why that's right? qemu_disable_default_devices()
isn't creating any devices at all, so it's not clear to me
(a) why it's setting vga_interface_type or (b) why setting
vga_interface_created to true is OK.

What I would have expected would have been some kind
of callback where the device created with -device whatever
arranged to set vga_interface_type to VGA_DEVICE when
it was created; but that's clearly not how the code works,
so I'm confused about how it does work...

thanks
-- PMM