Re: [PATCH net-next] net: lan966x: Fix when CONFIG_IPV6 is not set

The 02/09/2022 18:06, Jakub Kicinski wrote:

Hi Andrew, Jakub

On Wed, 9 Feb 2022 14:54:23 +0100 Andrew Lunn wrote:

quoted

On Wed, Feb 09, 2022 at 11:18:23AM +0100, Horatiu Vultur wrote:

quoted

When CONFIG_IPV6 is not set, then the compilation of the lan966x driver

compilation or linking?

It is a linking error. I will fix in the next version

quoted

quoted

fails with the following error:

drivers/net/ethernet/microchip/lan966x/lan966x_main.c:444: undefined
reference to `ipv6_mc_check_mld'

The fix consists in adding #ifdef around this code.

It might be better to add a stub function for when IPv6 is
disabled. We try to avoid #if in C code.

What do you think if I do something like this in the lan966x_main.h

---
#if IS_ENABLED(CONFIG_IPV6)
static inline bool lan966x_hw_offload_ipv6(struct sk_buff *skb)
{
	if (skb->protocol == htons(ETH_P_IPV6) &&
	    ipv6_addr_is_multicast(&ipv6_hdr(skb)->daddr) &&
	    !ipv6_mc_check_mld(skb))
		return false;

	return true;
}
#else
static inline bool lan966x_hw_offload_ipv6(struct sk_buff *skb)
{
	return false;
}
#endif
---

And then in lan966x_main.c just call this function.

If it's linking we can do:

        if (IS_ENABLED(CONFIG_IPV6) &&
            skb->protocol == htons(ETH_P_IPV6) &&
            ipv6_addr_is_multicast(&ipv6_hdr(skb)->daddr) &&
            !ipv6_mc_check_mld(skb))
                return false;

But beware that IPV6 can be a module, you may need a Kconfig dependency.

I was also looking at other drivers on how they use 'ipv6_mc_check_mld'.
Then I have seen that drivers/net/amt.c and net/bridge/br_multicast.c
they wrap this function with #if.
But then there is net/batman-adv/multicast.c which doesn't do that and
it can compile and link without CONFIG_IPV6 and I just don't see how
that is working.

-- 
/Horatiu