[Qemu-devel] Re: [PATCH RFC] net: add a flag to disable mac/vlan filtering

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Mar 09, 2010 at 05:30:31PM +0200, Michael S. Tsirkin wrote:
> On Tue, Mar 09, 2010 at 08:19:12AM -0700, Alex Williamson wrote:
> > On Tue, 2010-03-09 at 15:15 +0200, Michael S. Tsirkin wrote:
> > > diff --git a/hw/virtio-net.c b/hw/virtio-net.c
> > > index 5c0093e..01b45ed 100644
> > > --- a/hw/virtio-net.c
> > > +++ b/hw/virtio-net.c
> > > @@ -47,6 +47,7 @@ typedef struct VirtIONet
> > >      uint8_t nomulti;
> > >      uint8_t nouni;
> > >      uint8_t nobcast;
> > > +    uint32_t filtering;
> > >      struct {
> > >          int in_use;
> > >          int first_multi;
> > > @@ -475,12 +476,17 @@ static int receive_filter(VirtIONet *n, const uint8_t *buf, int size)
> > >          ptr += sizeof(struct virtio_net_hdr);
> > >      }
> > >  
> > > -    if (!memcmp(&ptr[12], vlan, sizeof(vlan))) {
> > > +    if ((n->filtering & (0x1 << NICCONF_F_VLAN_FILTERING)) &&
> > > +        !memcmp(&ptr[12], vlan, sizeof(vlan))) {
> > >          int vid = be16_to_cpup((uint16_t *)(ptr + 14)) & 0xfff;
> > >          if (!(n->vlans[vid >> 5] & (1U << (vid & 0x1f))))
> > >              return 0;
> > >      }
> > >  
> > > +    if (!(n->filtering & (0x1 << NICCONF_F_MAC_FILTERING))) {
> > > +            return 1;
> > > +    }
> > > +
> > 
> > A filtering flags bitmap is a logical choice here, but I found the
> > overhead to be non-trivial, which is why we have separate variables for
> > the other filtering options.
> 
> You suggest more flags for multicast etc?

Might not be a bad idea: e.g. tap filtering table in kernel
is limited in size, so we might win from only downloading
necessary mac addresses there.

> > >      if (ptr[0] & 1) { // multicast
> > >          if (!memcmp(ptr, bcast, sizeof(bcast))) {
> > >              return !n->nobcast;
> > > @@ -863,6 +869,8 @@ VirtIODevice *virtio_net_init(DeviceState *dev, NICConf *conf)
> > >  
> > >      n->mac_table.macs = qemu_mallocz(MAC_TABLE_ENTRIES * ETH_ALEN);
> > >  
> > > +    n->filtering = conf->filtering;
> > > +
> > 
> > Since we're not touching this in the savevm code, I assume the intention
> > is that we can transparently migrate between filtered bridges and
> > non-filtered bridges, right?
> 
> Right.
> 
> >  Thanks,
> > 
> > Alex