Re: [Qemu-devel] pl031 time across vm save/reload

[Peter Maydell]

On Fri, 5 Jul 2019 at 10:48, Paolo Bonzini <address@hidden> wrote:
> You're right, the compatibility causes wrong behavior for the default
> -rtc settings (the RC pauses across migration).  The right thing to do
> would be to store the base rather than the offset: that is, you store
> the time at which LR was written.  Then the offset is s->lr - s->base
> and it's independent of the machine on which the rtc_clock is being read.

So I thought I'd try writing a patch for this today, but I'm kind
of confused. If I understand you correctly, you're suggesting
that we should migrate a new field:
  base_time = s->lr - s->tick_offset
and then on the destination we can reconstitute tick_offset with
  s->tick_offset = base_time - s->lr
right?

But isn't this just a confusing way of migrating s->tick_offset
directly ? We'll never end up with a value at the destination
that's different from the offset value we started with on the source.

thanks
-- PMM