Re: [RFC PATCH v2 02/20] hw/core/qdev: Add vmstate_qdev_no_state_to_migrate

[Peter Maydell]

On Sun, 17 Jan 2021 at 19:25, Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:
>
> Add vmstate_qdev_no_state_to_migrate, which is simply a
> pointer to vmstate_no_state_to_migrate. This way all
> qdev devices (including "hw/qdev-core.h") don't have to
> include "migration/vmstate.h".
>
> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> ---
> Unresolved issues:
>
> https://www.mail-archive.com/qemu-devel@nongnu.org/msg721695.html
> Peter:
> > Does this definitely not put any data into the migration stream?
> > We don't want to change what's on the wire for machines that
> > use devices that start using this. (If it does by default, it
> > would be easy to make the migration code special case the
> > magic symbol to act like "no vmsd specified").
>
> https://www.mail-archive.com/qemu-devel@nongnu.org/msg727634.html
> Dave:
> > I'd need to test it to be sure, but I think if we added a .needed
> > to vmstate_no_state_to_migrate with a function that always returned
> > false, then I think the stream would stay unchanged.
> ---

It should be easy to test -- just do a 'savevm' of a running
system with a machine model that uses one of the devices that
has been marked as "no state to migrate", then apply the patchseries,
and see if 'loadvm' works or not.

thanks
-- PMM