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From: "Michael S. Tsirkin" <mst@redhat.com>
To: Rusty Russell <rusty@rustcorp.com.au>
Cc: QEMU-devel <qemu-devel@nongnu.org>, quintela@redhat.com
Subject: Re: [Qemu-devel] [PATCH] virtio: verify that all outstanding buffers are flushed (was Re: vmstate conversion for virtio?)
Date: Mon, 10 Dec 2012 22:35:12 +0200	[thread overview]
Message-ID: <20121210203512.GA1418@redhat.com> (raw)
In-Reply-To: <20121205110807.GA10045@redhat.com>

On Wed, Dec 05, 2012 at 01:08:07PM +0200, Michael S. Tsirkin wrote:
> Add sanity check to address the following concern:
> 
> On Wed, Dec 05, 2012 at 09:47:22AM +1030, Rusty Russell wrote:
> > All we need is the index of the request; the rest can be re-read from
> > the ring.
> 
> I'd like to point out that this is not generally
> true if any available requests are outstanding.
> Imagine a ring of size 4.
> Below A means available U means used.
> 
> A 1
> A 2
> U 2
> A 2
> U 2
> A 2
> U 2
> A 2
> U 2
> 
> At this point available ring has wrapped around, the only
> way to know head 1 is outstanding is because backend
> has stored this info somewhere.
> 
> The reason we manage to migrate without tracking this in migration
> state is because we flush outstanding requests before
> migration.
> This flush is device-specific though, let's add
> a safeguard in virtio core to ensure it's done properly.
> 
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

Doh sent a wrong patch sorry. I'll resend the right one shortly.
Pls disregard.

> ---
> 
> diff --git a/hw/virtio.c b/hw/virtio.c
> index f40a8c5..b80a5a9 100644
> --- a/hw/virtio.c
> +++ b/hw/virtio.c
> @@ -788,6 +788,8 @@ void virtio_save(VirtIODevice *vdev, QEMUFile *f)
>          if (vdev->vq[i].vring.num == 0)
>              break;
>  
> +        assert(!vq->inuse);
> +
>          qemu_put_be32(f, vdev->vq[i].vring.num);
>          qemu_put_be64(f, vdev->vq[i].pa);
>          qemu_put_be16s(f, &vdev->vq[i].last_avail_idx);
> 
> -- 
> MST

      parent reply	other threads:[~2012-12-10 20:32 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-12-04  3:09 [Qemu-devel] vmstate conversion for virtio? Rusty Russell
2012-12-04  6:30 ` Michael S. Tsirkin
2012-12-04 11:44 ` Juan Quintela
2012-12-04 23:17   ` Rusty Russell
2012-12-05 11:08     ` [Qemu-devel] [PATCH] virtio: verify that all outstanding buffers are flushed (was Re: vmstate conversion for virtio?) Michael S. Tsirkin
2012-12-06  6:03       ` Rusty Russell
2012-12-06  8:02         ` Michael S. Tsirkin
2012-12-06 23:39           ` Rusty Russell
2012-12-10 14:16             ` Anthony Liguori
2012-12-10 23:54               ` Rusty Russell
2012-12-10 20:35       ` Michael S. Tsirkin [this message]

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