Re: [QEMU PATCH v4 1/3] virtio-net: remove layout assumptions for ctrl vq

[Stefan Hajnoczi <stefanha@redhat.com>]

On Tue, Jan 22, 2013 at 10:38:14PM +0800, Amos Kong wrote:
> On Mon, Jan 21, 2013 at 05:03:30PM +0100, Stefan Hajnoczi wrote:
> > On Sat, Jan 19, 2013 at 09:54:26AM +0800, akong@redhat.com wrote:
> > > From: "Michael S. Tsirkin" <mst@redhat.com>
> > > 
> > > Virtio-net code makes assumption about virtqueue descriptor layout
> > > (e.g. sg[0] is the header, sg[1] is the data buffer).
> > > 
> > > This patch makes code not rely on the layout of descriptors.
> > > 
> > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > > Signed-off-by: Amos Kong <akong@redhat.com>
> > > ---
> > >  hw/virtio-net.c | 128 ++++++++++++++++++++++++++++++++------------------------
> > >  1 file changed, 74 insertions(+), 54 deletions(-)
> > > 
> > > diff --git a/hw/virtio-net.c b/hw/virtio-net.c
> > > index 3bb01b1..113e194 100644
> > > --- a/hw/virtio-net.c
> > > +++ b/hw/virtio-net.c
> > > @@ -315,44 +315,44 @@ static void virtio_net_set_features(VirtIODevice *vdev, uint32_t features)
> > >  }
> > >  
> > >  static int virtio_net_handle_rx_mode(VirtIONet *n, uint8_t cmd,
> > > -                                     VirtQueueElement *elem)
> > > +                                     struct iovec *iov, unsigned int iov_cnt)
> > >  {
> > >      uint8_t on;
> > > +    size_t s;
> > >  
> > > -    if (elem->out_num != 2 || elem->out_sg[1].iov_len != sizeof(on)) {
> > > -        error_report("virtio-net ctrl invalid rx mode command");
> > > -        exit(1);
> > > +    s = iov_to_buf(iov, iov_cnt, 0, &on, sizeof(on));
> > > +    if (s != sizeof(on)) {
> > > +        return VIRTIO_NET_ERR;
> > >      }
> > >  
> > > -    on = ldub_p(elem->out_sg[1].iov_base);
> > > -
> > > -    if (cmd == VIRTIO_NET_CTRL_RX_MODE_PROMISC)
> > > +    if (cmd == VIRTIO_NET_CTRL_RX_MODE_PROMISC) {
> > >          n->promisc = on;
> > > -    else if (cmd == VIRTIO_NET_CTRL_RX_MODE_ALLMULTI)
> > > +    } else if (cmd == VIRTIO_NET_CTRL_RX_MODE_ALLMULTI) {
> > >          n->allmulti = on;
> > > -    else if (cmd == VIRTIO_NET_CTRL_RX_MODE_ALLUNI)
> > > +    } else if (cmd == VIRTIO_NET_CTRL_RX_MODE_ALLUNI) {
> > >          n->alluni = on;
> > > -    else if (cmd == VIRTIO_NET_CTRL_RX_MODE_NOMULTI)
> > > +    } else if (cmd == VIRTIO_NET_CTRL_RX_MODE_NOMULTI) {
> > >          n->nomulti = on;
> > > -    else if (cmd == VIRTIO_NET_CTRL_RX_MODE_NOUNI)
> > > +    } else if (cmd == VIRTIO_NET_CTRL_RX_MODE_NOUNI) {
> > >          n->nouni = on;
> > > -    else if (cmd == VIRTIO_NET_CTRL_RX_MODE_NOBCAST)
> > > +    } else if (cmd == VIRTIO_NET_CTRL_RX_MODE_NOBCAST) {
> > >          n->nobcast = on;
> > > -    else
> > > +    } else {
> > >          return VIRTIO_NET_ERR;
> > > +    }
> > >  
> > >      return VIRTIO_NET_OK;
> > >  }
> > >  
> > >  static int virtio_net_handle_mac(VirtIONet *n, uint8_t cmd,
> > > -                                 VirtQueueElement *elem)
> > > +                                 struct iovec *iov, unsigned int iov_cnt)
> > >  {
> > >      struct virtio_net_ctrl_mac mac_data;
> > > +    size_t s;
> > >  
> > > -    if (cmd != VIRTIO_NET_CTRL_MAC_TABLE_SET || elem->out_num != 3 ||
> > > -        elem->out_sg[1].iov_len < sizeof(mac_data) ||
> > > -        elem->out_sg[2].iov_len < sizeof(mac_data))
> > > +    if (cmd != VIRTIO_NET_CTRL_MAC_TABLE_SET) {
> > >          return VIRTIO_NET_ERR;
> > > +    }
> > >  
> > >      n->mac_table.in_use = 0;
> > >      n->mac_table.first_multi = 0;
> > > @@ -360,54 +360,71 @@ static int virtio_net_handle_mac(VirtIONet *n, uint8_t cmd,
> > >      n->mac_table.multi_overflow = 0;
> > >      memset(n->mac_table.macs, 0, MAC_TABLE_ENTRIES * ETH_ALEN);
> > >  
> > > -    mac_data.entries = ldl_p(elem->out_sg[1].iov_base);
> > > +    s = iov_to_buf(iov, iov_cnt, 0, &mac_data.entries,
> > > +                   sizeof(mac_data.entries));
> 
> Hi Stefan, can we adjust the endianness after each iov_to_buf() copy?

Yes.

It's only necessary for uint16_t and larger types since a single byte
cannot be swapped (so ldub_p() is not needed).

Stefan