Re: [PATCH v3 05/11] pckbd: don't update OBF flags if KBD_STAT_OBF is set

[Gerd Hoffmann]

  Hi,

>  static const VMStateDescription vmstate_kbd = {
>      .name = "pckbd",
> -    .version_id = 3,
> +    .version_id = 4,
>      .minimum_version_id = 3,
>      .post_load = kbd_post_load,
>      .fields = (VMStateField[]) {
> @@ -435,6 +471,7 @@ static const VMStateDescription vmstate_kbd = {
>          VMSTATE_UINT8(status, KBDState),
>          VMSTATE_UINT8(mode, KBDState),
>          VMSTATE_UINT8(pending, KBDState),
> +        VMSTATE_UINT8_V(obdata, KBDState, 4),
>          VMSTATE_END_OF_LIST()
>      },
>      .subsections = (const VMStateDescription*[]) {
> @@ -512,12 +549,20 @@ void i8042_setup_a20_line(ISADevice *dev, qemu_irq 
> a20_out)
>      qdev_connect_gpio_out_named(DEVICE(dev), I8042_A20_LINE, 0, a20_out);
>  }

Unfortunately live migration isn't that easy.  Reason is we want able to
live-migrate both ways (old qemu -> new qemu but also new qemu -> old qemu).
With version ids we can do old qemu -> new qemu only.

So the usual way to deal with this is that new features which require
additional state information can be enabled/disabled at runtime using
device properties.  The feature is turned off for the compatibility
machine types.  The additional state is added using a conditional
subsection, which is only sent in case the feature is enabled.  That way
qemu with -- says -- "-machine pc-q35-5.0" will only enable features and
sent vmstate which qemu 5.0 is able to deal with.

I think there is no way around such a property for the ps2 fixes, even
if we use it for sending/not sending the additional ps2 state
information needed by the bugfixes.  Making the fixes itself conditional
should not be needed I think.

take care,
  Gerd