Re: [PATCH net-next v3 3/6] net: bcmgenet: add basic XDP support (PASS/DROP)

[Florian Fainelli]

On 3/30/26 15:01, Nicolai Buchwitz wrote:
> On 30.3.2026 20:15, Mohsin Bashir wrote:
> > > +static int bcmgenet_xdp_setup(struct net_device *dev,
> > > +                  struct netdev_bpf *xdp)
> > > +{
> > > +    struct bcmgenet_priv *priv = netdev_priv(dev);
> > > +    struct bpf_prog *old_prog;
> > > +    struct bpf_prog *prog = xdp->prog;
> > > +
> > > +    if (prog && dev->mtu > PAGE_SIZE - GENET_RX_HEADROOM -
> > > +        SKB_DATA_ALIGN(sizeof(struct skb_shared_info))) {
> > > +        NL_SET_ERR_MSG_MOD(xdp->extack,
> > > +                   "MTU too large for single-page XDP buffer");
> > > +        return -EOPNOTSUPP;
> > > +    }
> >
> > The MTU check here is great. But I do not see support 
> > for .ndo_change_mtu. This would allow users to change MTU size AFTER 
> > the program is attached.
>
> Good point. I had planned to add ndo_change_mtu in a follow-up series, 
> but this leaves a gap where MTU can be changed while XDP is attached.
>
> Options:
> 1. Add a minimal ndo_change_mtu to this series that only rejects MTU 
> changes incompatible with XDP, default behavior otherwise

Option 1 seems to be the simplest yet getting you a path through merging 
XDP support.

> 2. Reject any MTU change while XDP is attached
> 3. Defer to the ndo_change_mtu follow-up series
>
> Thoughts?
>
> Thanks
> Nicolai


--
Florian