STRUCT RSEQ_EVENT(9)

💅 struct rseq_event

okay so bestie, welcome to the <purple>struct rseq_event</purple> page from the Kernel API Manual — this is the little storage blob that keeps track of all the rseq-related event management business. it's giving "tiny struct, huge responsibilities" and honestly? iconic. ✨

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🦋 NAME

struct rseq_event — Storage for rseq related event management 💖

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🌸 SYNOPSIS

struct rseq_event {
    union {
      u64 all;
      struct {
        union {
          u32 events;
          struct {
            u8 sched_switch;
            u8 ids_changed;
            u8 user_irq;
          };
        };
        u8 has_rseq;
        u8 __pad;
        union {
          u16 error;
          struct {
            u8 fatal;
            u8 slowpath;
          };
        };
      };
    };
 };

like… look at all those anonymous unions. nested. layered. all on top, little u8s down at the bottom. it's a whole vibe pyramid 🎀

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🫶 MEMBERS

okay so here's the tour, member by member, no skips 👑

• {unnamed_union} — anonymous 🫧 (yes really, that's the whole description, she's mysterious)
• all — Compound to initialize and clear the data efficiently. this is the "grab the whole thing in one go" field, bestie. efficient queen 💅
• {unnamed_struct} — anonymous 🌸
• {unnamed_union} — anonymous ✨ (we love a recurring bit)
• events — Compound to access events with a single load/store. one load, one store, no mess 🔥
• {unnamed_struct} — anonymous 🦋
• sched_switch — True if the task was scheduled and needs update on exit to user. so like, "hey you got scheduled, remember to update when you go back to userspace" 😭
• ids_changed — Indicator that IDs need to be updated. the IDs are changing, the IDs are changing 💫
• user_irq — True on interrupt entry from user mode. loud and interrupting, we stan ⚡
• has_rseq — Greater than 0 if the task has a rseq pointer installed. Contains the RSEQ version number. so it's a bool and a version field, she contains multitudes 💜
• {unnamed_union} — anonymous 🍓
• error — Compound error code for the slow path to analyze. the slow path is gonna read this and figure out what went wrong 🙈
• {unnamed_struct} — anonymous 🧚
• fatal — User space data corrupted or invalid. bad vibes only, this one's serious 💀
• slowpath — Indicator that slow path processing via TIF_NOTIFY_RESUME is required. "notify me when you resume," basically 📬

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🌈 DESCRIPTION

so the actual rules of the house: sched_switch and ids_changed must be adjacent, and the combo must be 16bit aligned — all of that so the scheduler can do a single store when both of them get set at the same time. one store. both flags. chefs kiss 👑✨

like don't be reordering them, bestie, the whole single-store trick falls apart. respect the layout fr fr.

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⭐ SEE ALSO

• Kernel file ./include/linux/rseq_types.h
• struct rseq_ids(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)

go read them, iykyk 🦋💖

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and that's the page!! brought to you by ./include/linux, dated October 2026 — mwah, ily, go read your structs 💅🎀🫶