Re: [PATCH RFC net-next 1/2] hsr: Allow to send a specific port and with HSR header

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

On 2026-02-04 12:30:47 [-0500], Willem de Bruijn wrote:
> > --- a/include/linux/skbuff.h
> > +++ b/include/linux/skbuff.h
> > @@ -605,6 +605,7 @@ struct skb_shared_info {
> >  	};
> >  	unsigned int	gso_type;
> >  	u32		tskey;
> > +	u32		hsr_ptp;
> 
> skb_shared_info cannot easily be expanded.
> 
> This is too specific a use-case to warrant fields in every packet.
> 
> I'm not super familiar with High-availability Seamless Redundancy
> (HSR). Perhaps you can use either an skb_extension. Or the skb->cb[]
> field if this data is only needed within the HSR protocol logic, so
> can be assured to not be overwritten by other users of the control
> block.

skb->cb does not work because I need share it between the HSR stack
and AF_PACKET so it gets overwritten (as it is no meant to be shared
between layers).
I need actually three bits: HAVE_HEADER and PORT_NUMBER which 0-2.
Would it work if I add a :1 and :2 member to struct sk_buff into the
header group after unreadable? In my config there is a 6bit + 1 byte
hole. Worst case (all ifdefs enabled) it sums to 30 bits so I would have
just 2 left. Exceeding it by one bit in this case would extend create a
7bit + 1 byte hole and shift shifts tc_index + alloc_cpu. However there
is a two byte hole between alloc_cpu before csum which is removed then.

Would it be okay if I occupy three bits in sk_buff which look unused?

Sebastian