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From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <7d034a73-77d6-d79f-7b7b-137d8408e514@redhat.com>
Date: Thu, 15 Sep 2016 11:25:36 +0200
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Subject: Re: [Qemu-devel] [PATCH v2 02/10] block: set snapshot option for
 block devices in blkreplay module
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To: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru>, qemu-devel@nongnu.org
Cc: peter.maydell@linaro.org, mst@redhat.com, jasowang@redhat.com, quintela@redhat.com, agraf@suse.de, david@gibson.dropbear.id.au



On 15/09/2016 11:00, Pavel Dovgalyuk wrote:
> diff --git a/docs/replay.txt b/docs/replay.txt
> index 347b2ff..5be8f25 100644
> --- a/docs/replay.txt
> +++ b/docs/replay.txt
> @@ -196,6 +196,14 @@ is recorded to the log. In replay phase the queue =
is matched with
>  events read from the log. Therefore block devices requests are process=
ed
>  deterministically.
> =20
> +blkdriver also supports overlay option, which allows creating persiste=
nt
> +overlay file for saving and reloading VM snapshots in record/replay mo=
des.
> +Replay mechanism automatically creates one snapshot named 'replay_init=
' to
> +allow rewinding execution while replaying.
> +Overlay file may be specified as follows:
> + -drive driver=3Dblkreplay,if=3Dnone,image=3Dimg-direct,
> +        overlay=3Doverlay.qcow2,id=3Dimg-blkreplay

So in this case the image is actually overlay.qcow2, and it is created=20
with img-direct as the backing file?  Since you have to create=20
overlay.qcow2 outside QEMU anyway, overlay.qcow2 might as well be the=20
"image".  That is, you could choose between:

   -drive driver=3Dblkreplay,if=3Dnone,image=3Doverlay.qcow2,id=3Dimg-blk=
replay \
   -rr snapshot=3Dreplay_init,...

   -drive driver=3Dblkreplay,if=3Dnone,image=3Dimg-direct,id=3Dimg-blkrep=
lay

The temporary snapshot would be created if there's no "-rr snapshot" opti=
on
on the command line.

Does this make sense?

Paolo

>=20
> +static QemuOptsList blkreplay_runtime_opts =3D {
> +    .name =3D "quorum",

Pasto. ;)

> +    .head =3D QTAILQ_HEAD_INITIALIZER(blkreplay_runtime_opts.head),
> +    .desc =3D {
> +        {
> +            .name =3D "overlay",
> +            .type =3D QEMU_OPT_STRING,
> +            .help =3D "Optional overlay file for snapshots",
> +        },
> +        { /* end of list */ }
> +    },
> +};