Re: [PATCH net-next v5 3/8] hsr: Add a magic header for sending PTP packets

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2026-05-29 15:58:28 [-0400], Willem de Bruijn wrote:
> > --- a/net/hsr/hsr_device.c
> > +++ b/net/hsr/hsr_device.c
> > @@ -223,24 +223,61 @@ static netdev_features_t hsr_fix_features(struct net_device *dev,
> >  
> >  static netdev_tx_t hsr_dev_xmit(struct sk_buff *skb, struct net_device *dev)
> >  {
> > +	enum hsr_port_type tx_port = HSR_PT_NONE;
> >  	struct hsr_priv *hsr = netdev_priv(dev);
> >  	struct hsr_port *master;
> > +	bool has_header = false;
> >  
> >  	rcu_read_lock();
> >  	master = hsr_port_get_hsr(hsr, HSR_PT_MASTER);
> > -	if (master) {
> > -		skb->dev = master->dev;
> > -		skb_reset_mac_header(skb);
> > -		skb_reset_mac_len(skb);
> > -		spin_lock_bh(&hsr->seqnr_lock);
> > -		hsr_forward_skb(skb, master);
> > -		spin_unlock_bh(&hsr->seqnr_lock);
> > -	} else {
> > -		dev_core_stats_tx_dropped_inc(dev);
> > -		dev_kfree_skb_any(skb);
> > +	if (!master)
> > +		goto drop;
> > +
> > +	skb->dev = master->dev;
> > +	if (skb->protocol == htons(ETH_P_1588)) {
> > +		struct hsr_inline_header *hsr_opt;
> > +		unsigned int hdr_len;
> > +
> > +		BUILD_BUG_ON(sizeof(struct hsr_inline_header) != sizeof(struct ethhdr));
> > +
> > +		/* need to access the magic header */
> > +		if (!pskb_may_pull(skb, sizeof(struct hsr_inline_header)))
> > +			goto drop;
> > +
> > +		hsr_opt = (struct hsr_inline_header *)skb_mac_header(skb);
> > +		if (hsr_opt->magic == htonl(HSR_INLINE_HDR)) {
> > +			struct ethhdr *eth_hdr;
> > +
> > +			has_header = hsr_opt->hsr_hdr;
> > +			tx_port = hsr_opt->tx_port;
> > +			if (tx_port != HSR_PT_SLAVE_A && tx_port != HSR_PT_SLAVE_B)
> > +				goto drop;
> > +
> > +			eth_hdr = skb_pull(skb, sizeof(struct hsr_inline_header));
> > +			if (has_header)
> > +				hdr_len = ETH_HLEN + HSR_HLEN;
> > +			else
> > +				hdr_len = ETH_HLEN;
> > +			skb_set_network_header(skb, hdr_len);
> > +			/* Ensure the header can be accessed */
> > +			if (!pskb_may_pull(skb, hdr_len))
> > +				goto drop;
> > +			skb->protocol = eth_hdr->h_proto;
> > +		}
> 
> Should the packet be dropped otherwise?

We could make the inline header mandatory. Before this change sending
would not work anyway so this wouldn't break anything.
On the HSR side it mandatory and on PRP the stack isn't used here.
Nothing broke after testing. Let me drop the packet if the header is
missing.

Thank you Willem.

> >  	}

Sebastian