udp_tunnel6_dst_lookup(9)

📦 version 7.3.1, in nixpkgs unstable

✨ udp_tunnel6_dst_lookup(9) ✨

okay so bestie, welcome to the Kernel API Manual — this one's a kernel function, udp_tunnel6_dst_lookup(9), and it's literally the vibe check your UDP tunnel does before it commits to a route. no cap. 🦋

🌸 NAME 🌸

udp_tunnel6_dst_lookup — perform route lookup on UDP tunnel

like, that's the whole job description and she ate 💅

🎀 SYNOPSIS 🎀

struct dst_entry * udp_tunnel6_dst_lookup (struct sk_buff *skb , struct
net_device *dev , struct net *net , struct sock *sk , int oif , struct
in6_addr *saddr , const struct ip_tunnel_key *key , __be16 sport ,
__be16 dport , u8 dsfield , struct dst_cache *dst_cache );

she returns a struct dst_entry * and takes eleven arguments, which is honestly a lot of arguments but okay periodt 🫶

💖 ARGUMENTS 💖

  • skb — Packet for which lookup is done. the little packet that's getting its route figured out 📦
  • dev — Tunnel device 🌈
  • net — Network namespace of tunnel device
  • sk — Socket which provides route info
  • oif — Index of the output interface
  • saddr — Memory to store the src ip address. yes bestie, she writes into this — it's an out-param ✨
  • key — Tunnel information
  • sport — UDP source port
  • dport — UDP destination port
  • dsfield — The traffic class field
  • dst_cache — The dst cache to use for lookup. This function performs a route lookup on a UDP tunnel 👑

🧚 DESCRIPTION 🧚

okay so here's the tea — on success it returns a valid dst pointer and stores the src address to be used in the tunnel in the param saddr. if it's not a success? it hands you back a pointer encoded error code instead. so like, check your vibes before you dereference, iykyk 💀

bestie pls remember: the error comes back as a pointer encoded error code, not a plain NULL. do not just casually deref it, that's giving undefined behaviour and we don't do that here 😭

🔥 SEE ALSO 🔥

  • Kernel file ./net/ipv6/ip6_udp_tunnel.c

go read the source, she's iconic ⭐

and that's the whole page, bestie — mwah 💋 this one's from ./net/ipv6, dated October 2026, and she's filed under udp_tunnel6_dst_lookup(9). slay 🎀

📦 where this page comes from