Hi, Stefan Thanks for your response.
2011/12/30 Stefan Hajnoczi <stefa...@gmail.com> > > On Wed, Dec 28, 2011 at 06:16:42PM +0800, Ying-Shiuan Pan wrote: > > I'm very interested in virtio-mmio Peter Maydell did for QEMU, > > (http://lists.nongnu.org/archive/html/qemu-devel/2011-11/msg01870.html) > > > > actually, I've tested the virtio-blk, and it is working. > > I applied those patch to QEMU-1.0 and brought the virtio_mmio.c from > > Linux-3.2-rc back to Linux-linaro-2.6.38. > > > > I also found a small bug in virito-mmio.c: virtio_mmio_write(), > > Peter forgot to break in each case of switch block. > > After fixed the small bug, the virtio-balloon works as well. > > PMM: Do you have a git branch where you could apply Ying-Shiuan's fix? hmm... I've sent Peter my patch :) > > > Then, when I attempted to enable the virtio-net, the initialization part is > > fine, > > however, the QEMU crashed and printed this message: > > "virtio-net header not in first element" > > > > It happens when the front-end virtio-net is invoking virtqueue_kick() at > > the end of try_fill_recv(). > > Then, QEMU gets this message and invokes virtio_net_receive(), then the > > error happens. > > virtio-net is looking at a virtqueue element (a packet buffer provided > by the guest OS into which QEMU will copy the received packet) but the > virtqueue element does not have the expected format. You can check the > virtio specification for the details on the virtio-net buffer layout: > http://ozlabs.org/~rusty/virtio-spec/ > > It sounds like the vring is corrupted or QEMU's virtio code is not > correctly reading the virtqueue element (which is basically an iovec > array). > > virtio-net is more advanced than virtio-blk in how it uses virtio so > it's not surprising that you've discovered an issue. Debugging this > comes down to looking at the vring descriptors and the virtqueue > elements that QEMU extracts. > > It sounds like there's a problem with the rx queue, you could try > indirect_desc=off to disable indirect vring descriptors to see if that > is part of the problem. > > Stefan I guessed that the problem was in adding header, virtio-net should insert its header to the ring buffer before its packet, correct me if I'm wrong. virtio-net driver (backend part) can use add_recvbuf_small() / add_recvbuf_big() / add_recvbuf_mergeable() depending on what features the virtio-net device (QEMU part) provides. I found that both small and big add the header, while the mergeable one does not. Besides, in that add_recvbuf_big(), the comments mentioned about a QEMU bug?? Anyway, I found a workaround solution, that is disable the VIRTIO_NET_F_MRG_RXBUF feature and make virtio-net driver use add_recvbuf_big() However, I am still not clear about how the problem happened. If I luckily figure out, I'll post it. :) So~ currently, virito-balloon, virtio-blk, and virtio-net can work properly with virtio-mmio. :D The following is the *workaround solution* which is for virtio-net driver part (frontend). diff --git a/virtio_net.c b/virtio_net.c index 82dba5a..811e2d9 100644 --- a/virtio_net.c +++ b/virtio_net.c @@ -955,8 +955,10 @@ static int virtnet_probe(struct virtio_device *vdev) virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_ECN)) vi->big_packets = true; +#ifndef ARM if (virtio_has_feature(vdev, VIRTIO_NET_F_MRG_RXBUF)) vi->mergeable_rx_bufs = true; +#endif /* We expect two virtqueues, receive then send, * and optionally control. */ ---- Best Regards, Ying-Shiuan Pan
