Oliver Hartkopp wrote:

Patrick McHardy wrote:

quoted

skb->sk should work here as well since you detect these frames
before queueing to the receiving socket.
 

Hm - this would indeed be much nicer than using skb->cb.

I think we just had some concerns to use skb->sk for our own
functionality, as it might be used and dereferenced by other layers
between the socket and the network driver ... so setting skb->sk to NULL
(to indicate 'no loopback') smells bad if you don't really know who ever
dereferences skb->sk.

Indeed, that will break things.

Btw. it's really worth to look at it again. I just had the idea to
access the loopback flag via skb->sk->opt->loopback (argpfl!) on the TX
path and skb->sk on the RX path. This would avoid skb->sk to be set to
NULL but need to have this loopback flag to be implemented in each CAN
socket opt.

Yes, thats what I wanted to suggest. You should even be able
to use skb->sk->opt->loopback on the receive path before you
queue the packet to the socket.