Re: [Qemu-block] [PATCH v3 07/33] automatically add vmstate for reset support in devices

[Peter Maydell]

On Thu, 8 Aug 2019 at 16:42, Dr. David Alan Gilbert <address@hidden> wrote:
>
> * Peter Maydell (address@hidden) wrote:
> > On Mon, 29 Jul 2019 at 15:59, Damien Hedde <address@hidden> wrote:
> > >
> > > This add the reset related sections for every QOM
> > > device.
> >
> > A bit more detail in the commit message would help, I think --
> > this is adding extra machinery which has to copy and modify
> > the VMStateDescription passed in by the device in order to
> > add the subsection that handles reset.
> >
> > I've added Dave Gilbert to the already long cc list since this
> > is migration related.
>
> I don't like dynamically modifying all the vmsds.

Yeah, I'm not a huge fan of it either, but it does mean that
the state gets migrated and we don't have a pile of really
easy to miss bugs where we forgot to say "this device needs to
migrate the reset state" and it means we don't have every
device we ever write in the future needing to say "this device
needs to migrate reset state"...

> Aren't you going to have to understand each devices reset behaviour
> and make sure it does something sane? e.g. it might have a postload
> that registers a timer or something that you wouldn't want to do if it's
> in reset.
>
> The easiest way is to write a macro that you can easily add to devices
> you've checked subsection list (like the way we have a
> VMSTATE_USB_DEVICE).

One problem is that as soon as somebody writes a USB controller
or PCI controller model that can be held in reset, every
device that could sat behind it automatically now could find
that it's migrated while it's in reset.

thanks
-- PMM