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Date: Thu, 16 Oct 2014 12:09:30 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v3 2/2] Xen: Use the ioreq-server API when
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To: Paul Durrant <Paul.Durrant@citrix.com>, Peter Maydell <peter.maydell@linaro.org>
Cc: Olaf Hering <olaf@aepfle.de>, Alexey Kardashevskiy <aik@ozlabs.ru>, Stefan Weil <sw@weilnetz.de>, Michael Tokarev <mjt@tls.msk.ru>, QEMU Developers <qemu-devel@nongnu.org>, Alexander Graf <agraf@suse.de>, Stefano Stabellini <Stefano.Stabellini@citrix.com>, Gerd Hoffmann <kraxel@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>, "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>

Il 16/10/2014 10:25, Paul Durrant ha scritto:
>>> +static void xen_hvm_pre_save(void *opaque)
>>> +{
>>> +    XenIOState *state = opaque;
>>> +
>>> +    /* Stop servicing emulation requests */
>>> +    xen_set_ioreq_server_state(xen_xc, xen_domid, state->ioservid, 0);
>>> +    xen_destroy_ioreq_server(xen_xc, xen_domid, state->ioservid);
>>> +}
>>
>> Is the new use of vmstate_register() really necessary?
>> Usually the state you're saving corresponds to some QOM
>> device whose vmsd field you can use instead.
> 
> In this case, it seems like a job for a vmstate change handler.
> 
> I looked at that but it did not seem to give me the right semantic,
> whereas the pre-save callback gave me exactly the right semantic.

What exactly is the right semantics?  Note that save _can_ fail, so you
need the ability to roll back to the source machine.  I think this is
missing from your patch, and there is no post_save hook that you can use.

Paolo