From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:53418) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Tijr7-00045h-NB for qemu-devel@nongnu.org; Wed, 12 Dec 2012 05:48:09 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Tijqz-0007Hf-NO for qemu-devel@nongnu.org; Wed, 12 Dec 2012 05:48:01 -0500 Received: from mx1.redhat.com ([209.132.183.28]:25291) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Tijqz-0007HK-8A for qemu-devel@nongnu.org; Wed, 12 Dec 2012 05:47:53 -0500 Date: Wed, 12 Dec 2012 12:51:01 +0200 From: "Michael S. Tsirkin" Message-ID: <20121212105101.GA6461@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Subject: [Qemu-devel] [PATCHv2] virtio: verify that all outstanding buffers are flushed List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org, Rusty Russell Cc: Paolo Bonzini , Anthony Liguori , Avi Kivity , Stefan Hajnoczi , "Michael S. Tsirkin" Add sanity check to address the following concern: During migration, all we pass the index of the request; the rest can be re-read from the ring. This is not generally enough 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 --- Changes from v1: v1 was against the wrong tree, it didn't build against qemu.git hw/virtio.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/hw/virtio.c b/hw/virtio.c index f40a8c5..6227642 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(!vdev->vq[i].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