STRUCT RSEQ_IDS(9)

struct rseq_ids(9) 💅

Okay bestie, welcome to the Kernel API Manual page for struct rseq_ids — it's literally the cache for ids that need to be updated. Lowkey iconic little struct behavior. 🎀

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✨ NAME ✨

struct rseq_ids — Cache for ids, which need to be updated 💖

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🦋 SYNOPSIS 🦋

struct rseq_ids {
    union {
      u64 cpu_cid;
      struct {
        u32 cpu_id;
        u32 mm_cid;
      };
    };
    u32 node_id;
 };

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🌸 Members 🌸

• {unnamed_union} — anonymous. The manpage literally says anonymous, and honestly? Same. 🙈
• cpu_cid — compound of cpu_id and mm_cid to make the compiler emit a single compare on 64-bit. Not me being obsessed with one compare, it's just efficient queen behavior. ⚡
• {unnamed_struct} — anonymous.
• cpu_id — the CPU ID which was written last to user space. 💻
• mm_cid — the MM CID which was written last to user space. 🧚
• node_id — the node ID which was written last to user space. 🌈

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💜 Description 💜

So the whole vibe is: cpu_id, mm_cid and node_id are updated when the data is written to user space. That's it, that's the plot. ✨

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👑 SEE ALSO 👑

Kernel file ./include/linux/rseq_types.h and the whole friend group:

• struct rseq_event(9)
• union rseq_slice_state(9)
• struct rseq_slice(9)
• struct rseq_data(9)
• struct sched_mm_cid(9)
• struct mm_cid_pcpu(9)
• struct mm_mm_cid(9)

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Source: ./include/linux, dated October 2026, page struct rseq_ids(9). Periodt. 💋🫶