From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:44329) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TgCmn-0001Ag-O4 for qemu-devel@nongnu.org; Wed, 05 Dec 2012 06:05:13 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TgCmg-00037T-Gf for qemu-devel@nongnu.org; Wed, 05 Dec 2012 06:05:05 -0500 Received: from mx1.redhat.com ([209.132.183.28]:58115) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TgCmg-00037I-9D for qemu-devel@nongnu.org; Wed, 05 Dec 2012 06:04:58 -0500 Date: Wed, 5 Dec 2012 13:08:07 +0200 From: "Michael S. Tsirkin" Message-ID: <20121205110807.GA10045@redhat.com> References: <87624iikcw.fsf@rustcorp.com.au> <87zk1uca8z.fsf@elfo.mitica> <87r4n5h0fx.fsf@rustcorp.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87r4n5h0fx.fsf@rustcorp.com.au> Subject: [Qemu-devel] [PATCH] virtio: verify that all outstanding buffers are flushed (was Re: vmstate conversion for virtio?) List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Rusty Russell Cc: QEMU-devel , quintela@redhat.com 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 --- 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