STRUCT MFC_CACHE(9)

💖 struct mfc_cache(9) 💖

okay so this is a page straight out of the Kernel API Manual — yes bestie, the actual kernel docs — and it's all about struct mfc_cache, the little data structure that holds multicast routing entries 👑 ngl it's giving "plumbing that runs the internet" energy and we're obsessed.

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✨ NAME ✨

struct mfc_cache — multicast routing entries 🦋

Like, that's it, that's the whole vibe: this struct is the routing entry. Slay.

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🌸 SYNOPSIS 🌸

here's the shape, verbatim, do not come for me about the formatting, I did not write the kernel, I just live here 💅

struct mfc_cache {
    struct mr_mfc _c;
    union {
      struct {
        __be32 mfc_mcastgrp;
        __be32 mfc_origin;
      };
      struct mfc_cache_cmp_arg cmparg;
    };
 };

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🎀 Members 🎀

• _c — the Common multicast routing information, and it has to be first, literally, because of [for casting] — yeah, the whole casting trick depends on it sitting right up front. main character position, no cap 🔥
• {unnamed_union} — anonymous 👀 (that's the whole note, she's mysterious, she's unnamed)
• {unnamed_struct} — anonymous 🫶 (same deal, no name, just vibes)
• mfc_mcastgrp — the destination multicast group address — like, where the traffic is actually going 📬✨
• mfc_origin — the source address — where it came from in the first place 💫
• cmparg — used for rhashtable comparisons 🧚 this one's the compare key, the little gremlin that lets the hashtable tell entries apart

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⭐ SEE ALSO ⭐

• Kernel file ./include/linux/mroute.h — go read the source bestie, it ate 💀

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lowkey a warning from me to you: _c must be first. that's not a suggestion, that's the casting situation. respect it 🙈

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and that's the whole page!! short and iconic, just like her 💜

mwah, bye bestie 🎀 — this one came from the source dir ./include/linux, dated October 2026, and I hope you had as much fun as I did, which is a normal amount, periodt 💅🌈