STRUCT CLOCKSOURCE_HW_SNAPSHOT(9)

✨ struct clock..._hw_snapshot(9) ✨

okay bestie, welcome to the Kernel API Manual 💅 — this one's a struct page, and it's honestly kind of a big deal. Let's get into it 🫶

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🌸 NAME 🌸

struct clocksource_hw_snapshot — a Snapshot for the underlying hardware counter of derived clocksources like kvmclock or Hyper-V scaled TSC 🕰️✨

🦋 SYNOPSIS 🦋

struct clocksource_hw_snapshot {
    u64 hw_cycles;
    enum clocksource_ids    hw_csid;
 };

like. that's the whole thing. two members. main character energy fr 👑

🎀 Members 🎀

• hw_cycles — The hardware counter value 💖 literally just the raw hardware counter, sitting there, being a u64
• hw_csid — Clocksource ID of the hardware counter 🏷️ so you know which hardware counter we're talking about

⭐ Description ⭐

okay so here's the vibe: clocksources like this one (the derived ones, iykyk) must implement the read_snapshot callback 😤 no skipping, no cap.

And that callback has to:

• fill in the hardware counter value ✅
• fill in the clocksource ID of the hardware counter ✅
• derive the actual clocksource cycles from hw_cycles ✅

…and the whole point of doing all that? so the thing can provide an atomic snapshot 🔥 that's it, that's the goal, and it's iconic.

⚠️ lowkey important: the word "must" is doing real work here — the callback is required, not optional 🙈

🌈 SEE ALSO 🌈

go look at the Kernel file ./include/linux/clocksource.h for these besties 🫶:

• struct clocksource(9)
• clocksource_khz2mult(9)
• clocksource_hz2mult(9)
• clocksource_cyc2ns(9)
• struct clocksource_base(9)

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and that's the page!! 🎀 sign-off time: this lil slice of kernel lore lives in ./include/linux, dated October 2026, and it's filed under struct clock..._hw_snapshot(9) — the ellipsis is not a typo, it's a lifestyle 💀💜 go read your clocksources bestie!! 🧚✨