STRUCT ACTION_CACHE(9)

💅 struct action_cache(9) — like, the whole kernel API manual vibe 🎀

okay so bestie, welcome to the struct action_cache(9) page 💖 this is straight out of the Kernel API Manual, and it's genuinely such a cute little struct. let's get into it ✨

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🌸 NAME 🌸

struct action_cache — a per-filter cache of seccomp actions, one for each arch/syscall pair 🦋

like, per filter. per arch. per syscall. she's organised, she's tracking everything, she's that girl 💅

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✨ SYNOPSIS ✨

struct action_cache {
    unsigned long allow_native[BITS_TO_LONGS( SECCOMP_ARCH_NATIVE_NR)];
  #ifdef SECCOMP_ARCH_COMPAT;
    unsigned long allow_compat[BITS_TO_LONGS( SECCOMP_ARCH_COMPAT_NR)];
  #endif;
 };

no cap, this is the whole thing. two bitmaps and a dream 🫶

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🌈 Members 🌈

• allow_native — a bitmap where each bit is like "does this filter always allow this syscall?" for the native architecture. one bit, one verdict, no ambiguity 💫
• allow_compat — same energy, but for the compat architecture. that one's tucked behind #ifdef SECCOMP_ARCH_COMPAT; so she only shows up when compat arch is actually a thing, iykyk 🔥

lowkey the whole point is that each bit answers a yes/no for one syscall, so the filter doesn't have to redo the work every single time. iconic behaviour, honestly 👑

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🦋 SEE ALSO 🦋

the kernel file lives at ./kernel/seccomp.c — go say hi to her 💜 and while you're in there, the whole friend group:

• struct seccomp_kaddfd(9)
• struct notification(9)
• struct seccomp_filter(9)
• seccomp_check_filter(9)
• seccomp_cache_check_allow(9)
• seccomp_run_filters(9)
• seccomp_can_sync_threads(9)
• seccomp_filter_release(9)
• seccomp_sync_threads(9)
• seccomp_prepare_filter(9)
• seccomp_prepare_user_filter(9)
• seccomp_is_const_allow(9)
• seccomp_cache_prepare(9)
• seccomp_attach_filter(9)
• seccomp_set_mode_strict(9)
• seccomp_set_mode_filter(9)
• prctl_set_seccomp(9)

like, that's the entire group chat and every one of them ate 🔥

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and that's the page!! this one ships from ./kernel and it's dated October 2026, so yeah, she's stamped and official ⭐ mwah, go forth and cache those actions bestie 💖🧚‍♀️