build_udp_v6_csum(9)

💖 build_udp_v6_csum(9) 💖

okay so bestie, welcome to the Kernel API Manual page for build_udp_v6_csum ✨ this one lives over in the kernel API docs and it's honestly giving "small function, big job" energy 🫶

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✨ NAME ✨

build_udp_v6_csum — compute UDP checksum for UDP over IPv6 💅

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🌸 SYNOPSIS 🌸

__sum16 build_udp_v6_csum (const struct ipv6hdr *ip6h , const struct
udphdr *udph );

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🎀 ARGUMENTS 🎀

• ip6h — -- undescribed -- 🙈 (like, the manpage literally says this, no cap, it's not me gatekeeping)
• udph — -- undescribed -- 🫶 (same vibe, the docs left this one blank too)

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🦋 DESCRIPTION 🦋

So what does it actually do? It computes the checksum to embed in the UDP header 📝 That checksum is composed of:

• the sum of the IPv6 pseudo-header checksum
• the UDP header checksum
• the UDP data checksum

with ip6h being the IPv6 header and udph being the UDP header — and the UDP header must be immediately followed by UDP data. like, immediately immediately. main character adjacency required 👑

It returns the total checksum ⭐

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🌈 SEE ALSO 🌈

• Kernel file ./tools/testing/selftests/bpf/network_helpers.h
• open_netns(9)
• append_tid(9)
• csum_tcpudp_magic(9)
• csum_ipv6_magic(9)
• build_udp_v4_csum(9)
• tc_prog_attach(9)

iykyk, go read them, they're iconic 💜

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🍓 reminder: the UDP header has to be right there in front of the UDP data, or this whole checksum situation is not it. no cap.

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and that's the page bestie!! 🧚 this lil number comes to you from ./tools/testing/selftests/bpf, dated October 2026 — don't be a stranger 💖🎀