after malloc?

please, move decl before code

malloc in case of M_WAITOK can't return NULL

error = kern_sysctl
if (error != 0)

goto out;

out before free()

return (error);

btw, Is that enough? rtsock messages can be up to 64k

Ah, thank you. rib_walk was my first inclination but I wasn't sure if it'd return the information I needed. netstat(1) uses sysctl and thus provided an example on how to decode the results.

It does.

You'll get 'struct rtentry' in the iterator, which allows extracting prefix data via
rt_get_inet_prefix_pmask().
Nexthop is slightly more tricky, as there can be multiple paths attached to a single prefix, so you need something like sysctl_dumpentry() code.
Finally, you'll get the nexthop pointer, where you can easily get ifp (nh_ifp), mtu (nh_mtu), and gateway (gw_sa). Note that the gateway is only relevant if (nh_flags & NHF_GATEWAY) is true. Also, the gateway can be IPv6 for 4over6 routes.

You shouldn’t include it, that’s a private header for the routing code.

Probably worth using ‘struct in_addr’ here

Re multipath: to be safe probably worth using nhop_select(raw_nhop, 0) to ensure it doesnt crash with multipath routes

I’d suggest defining 0xF explicitely as a flag combination

You shouldn’t access rtentry fields directly, use rt_get_weight().

Worth using c11 initialisers:

You don’t need to hold ifnet lock, but you need to be in network epoch (NET_EPOCH_ENTER())

Without the ifnet lock, linux_ifname() panics due to IFNET_RLOCK_ASSERT()

panic: Lock (sx) ifnet_sx not locked

No good reason. :)