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Date: Tue, 09 Sep 2014 18:24:27 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 07/10] serial: fixing vmstate for
	save/restore
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To: quintela@redhat.com
Cc: amit.shah@redhat.com, qemu-devel@nongnu.org, Pavel.Dovgaluk@ispras.ru, dgilbert@redhat.com

Il 09/09/2014 15:59, Juan Quintela ha scritto:
> If it is still -1 at this point, we "calculate" a value for it.
> (I assume it is right, no knowledge of serial port)

Not necessarily right, or we wouldn't need the subsection, but at least
a decent approximation.

> But poll_msl is "more" interesting, because we are not "reseting it".
> 
> So, we have that if we are migrating from an old version, we would have
> poll_msl == -1, and we used to have it to poll_msl == 0.
> 
> Should we change it?
> 
> I think that putting:
> 
> s->poll_msl = 0;
> 
> in preload, and 
> 
> static bool serial_poll_needed(void *opaque)
> {
>     SerialState *s = opaque;
>     return s->poll_msl != 0;
> }
> 
> would give exactly the same behaviour for new qemus, and behave better
> for older ones?

poll_msl is usually -1, so the "needed" function must be like Pavel wrote.

poll_msl is only used for serial port passthrough, which I guess we can
say "just doesn't work" for migration on < 2.1.  In fact, putting
migration + passthrough together is probably not a great idea. :)  We
probably could drop ust the poll_msl/modem_status_poll subsection, but I
assume Pavel had some kind of test case.

Paolo