Re: [PATCH 07/13] RFC migration: icp/server is a mess

[Greg Kurz <groug@kaod.org>]

On Fri, 20 Oct 2023 09:30:44 +0200
Juan Quintela <quintela@redhat.com> wrote:

> Greg Kurz <groug@kaod.org> wrote:
> > On Thu, 19 Oct 2023 21:08:25 +0200
> > Juan Quintela <quintela@redhat.com> wrote:
> >
> >> Current code does:
> >> - register pre_2_10_vmstate_dummy_icp with "icp/server" and instance
> >>   dependinfg on cpu number
> >> - for newer machines, it register vmstate_icp with "icp/server" name
> >>   and instance 0
> >> - now it unregisters "icp/server" for the 1st instance.
> >> 
> >> This is wrong at many levels:
> >> - we shouldn't have two VMSTATEDescriptions with the same name
> >> - In case this is the only solution that we can came with, it needs to
> >>   be:
> >>   * register pre_2_10_vmstate_dummy_icp
> >>   * unregister pre_2_10_vmstate_dummy_icp
> >>   * register real vmstate_icp
> >> 
> >> As the initialization of this machine is already complex enough, I
> >> need help from PPC maintainers to fix this.
> >> 
> >> Volunteers?
> >> 
> >> CC: Cedric Le Goater <clg@kaod.org>
> >> CC: Daniel Henrique Barboza <danielhb413@gmail.com>
> >> CC: David Gibson <david@gibson.dropbear.id.au>
> >> CC: Greg Kurz <groug@kaod.org>
> >> 
> >> Signed-off-by: Juan Quintela <quintela@redhat.com>
> >> ---
> >>  hw/ppc/spapr.c | 7 ++++++-
> >>  1 file changed, 6 insertions(+), 1 deletion(-)
> >> 
> >> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> >> index cb840676d3..8531d13492 100644
> >> --- a/hw/ppc/spapr.c
> >> +++ b/hw/ppc/spapr.c
> >> @@ -143,7 +143,12 @@ static bool pre_2_10_vmstate_dummy_icp_needed(void *opaque)
> >>  }
> >>  
> >>  static const VMStateDescription pre_2_10_vmstate_dummy_icp = {
> >> -    .name = "icp/server",
> >> +    /*
> >> +     * Hack ahead.  We can't have two devices with the same name and
> >> +     * instance id.  So I rename this to pass make check.
> >> +     * Real help from people who knows the hardware is needed.
> >> +     */
> >> +    .name = "pre-2.10-icp/server",
> >>      .version_id = 1,
> >>      .minimum_version_id = 1,
> >>      .needed = pre_2_10_vmstate_dummy_icp_needed,
> >
> > I guess this fix is acceptable as well and a lot simpler than
> > reverting the hack actually. Outcome is the same : drop
> > compat with pseries-2.9 and older.
> >
> > Reviewed-by: Greg Kurz <groug@kaod.org>
> 
> I fully agree with you here.
> The other options given on this thread is deprecate that machines, but I
> would like to have this series sooner than 2 releases.

Yeah and, especially, the deprecation of all these machine types is
itself a massive chunk of work as it will call to identify and
remove other related workarounds as well. Given that pretty much
everyone working in PPC/PAPR moved away, can the community handle
such a big change ?

>  And what ppc is
> doing here is (and has always been) a hack and an abuse about how
> vmstate registrations is supposed to work.
> 

Sorry again... We should have involved migration experts at the time. :-)

> Thanks, Juan.
> 

Cheers,

-- 
Greg