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

[Nicolai Buchwitz]

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
2. Reject any MTU change while XDP is attached
3. Defer to the ndo_change_mtu follow-up series

Thoughts?

Thanks
Nicolai