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Date: Wed, 28 Jul 2010 19:23:50 +0800
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From: TeLeMan <geleman@gmail.com>
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Subject: [Qemu-devel] Re: [PATCH] vmstate: fix vmstate_subsection_load
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To: quintela@redhat.com
Cc: qemu-devel <qemu-devel@nongnu.org>

On Wed, Jul 28, 2010 at 18:43, Juan Quintela <quintela@redhat.com> wrote:
> TeLeMan <geleman@gmail.com> wrote:
>> =C2=A0If the new version adds the new subsection for some vmstate, the o=
ld
>> version will load the new version's vmstate unsuccessfully. So we have
>> to ignore the unrecognized subsections.
>
> No. =C2=A0That was the whole point of subsections. =C2=A0If one subsectio=
n is
> sent, target machine has to understand it. =C2=A0If it don't understand i=
t,
> it fails.
>
> If subsection is not needed, it is the responsability of the source to
> not send it.
>
> This was one of the design requirements. =C2=A0Subsections are optional b=
ut
> it is the source which decides which ones to send/not to send. =C2=A0The
> target has to understand everything that it gets or fail the migration.
>

If the target must understand everything, the vmstate's version will
be useless because the old version target maybe cannot load the new
version target's vmstate.