csum_ipv6_magic(9)

💖 csum_ipv6_magic(9) 💖

okay so bestie, welcome to the Kernel API Manual page for csum_ipv6_magic — yes that's the section 9 one, kernel-space girlies rise 🫶 this is the little helper that does the IPv6 pseudo-header checksum math for you so you don't have to ✨

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🌸 NAME 🌸

csum_ipv6_magic — compute IPv6 pseudo-header checksum

like literally that's it, that's the whole vibe 💅

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🎀 SYNOPSIS 🎀

__sum16 csum_ipv6_magic (const struct in6_addr *saddr , const struct
in6_addr *daddr , __u32 len , __u8 proto , __wsum csum );

she takes five args and gives you back a __sum16, periodt 👑

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🦋 ARGUMENTS 🦋

• saddr — the IPv6 source address, obvs 💖
• daddr — the IPv6 dest address, the other one bestie, don't mix them up 😭
• len — the IPv6 data size, an __u32, keep it cute
• proto — the transport layer protocol, an __u8, iykyk
• csum — the accumulated partial sum to add to the computation, like a little carry-over gift from the transport layer 🎁

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✨ DESCRIPTION ✨

So what she actually does: compute the ipv6 pseudo header checksum. That's the whole thing. 🌈

The helper can take a accumulated sum from the transport layer to accumulate it and directly return the transport layer. the way that works is so iconic honestly — you hand her your partial sum, she folds it in, and hands back something the transport layer can just use, no extra steps 🧚

Returns the folded sum. that's the return value bestie, don't lose it 💀

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👑 SEE ALSO 👑

Kernel file ./tools/testing/selftests/bpf/network_helpers.h — go read it fr fr 📖

• open_netns(9)
• append_tid(9)
• csum_tcpudp_magic(9)
• build_udp_v4_csum(9)
• build_udp_v6_csum(9)
• tc_prog_attach(9)

all the besties in the checksum-and-netns friend group, go say hi 🫶

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💜 and that's a wrap! this iconic little page lives under ./tools/testing/selftests/bpf and it's dated October 2026 — go forth and checksum, bestie, you've got this ⭐🔥🎀