STRUCT ALARM(9)

🎀 struct alarm(9) 🎀

okay bestie, welcome to section 9 of the Kernel API Manual — yes we're in the kernel API girlie corner now, and today's main character is struct alarm, aka the Alarm timer structure ✨

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💖 NAME 💖

struct alarm — the Alarm timer structure. that's it, that's the vibe. she's a struct, she holds an alarm timer, she slays 💅

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🌸 SYNOPSIS 🌸

here's the whole glow-up, copy-pasted exactly because we do NOT mess with code in this house:

struct alarm {
    struct timerqueue_node  node;
    struct hrtimer          timer;
    void (*function)(struct alarm *, ktime_t now);
    enum alarmtimer_type    type;
    int state;
    void *data;
 };

look at her. six members. absolutely iconic. no cap 🫶

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🦋 Members 🦋

okay so let's meet the cast, one by one, because every single one of them matters:

• node — the timerqueue node that gets you added to the event list. and plot twist: this value also includes the expiration time. two jobs, one field, main character energy fr fr 👑
• timer — the hrtimer that's used to schedule events while things are running. she's the one actually keeping time while the alarm is live ⏰
• function — a function pointer that gets executed when the timer fires. like, the callback. the moment of truth. the "it's happening" moment 😭🔥
• type — the alarm type, and your options are BOOTTIME / REALTIME. pick your clock, bestie 🕰️
• state — a flag that represents whether the alarm is set to fire or not. basically a yes/no girlie for "are we firing or are we not" 💀
• data — internal data value. that's it. that's the description. she's mysterious, she's private, she's internal 🙈

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🌈 SEE ALSO 🌈

• Kernel file ./include/linux/alarmtimer.h — go read the source, iykyk 📖✨

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and that's the whole page!! mwah 💋

friendly reminder that this beautiful little write-up lives under ./include/linux and it's dated October 2026 — so like, mark your calendar, bestie 🗓️💜

stay hydrated, read your headers, and don't forget to #include her 🧚‍♀️🌸