libnvme(9)

💜 libnvme(9) — okay bestie, let's talk about struct nvme_voltage_measurement_log

So this is a page from the libnvme API Manual — yes, the libnvme manual, section 9 — and today's main character is a lil struct that maps out the Voltage Measurement Log Page, aka Log Identifier 27h. It's giving "I measure volts and I take that seriously" ✨

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🌸 NAME 🌸

struct nvme_voltage_measurement_log — the Voltage Measurement Log Page, and yes bestie, that's Log Identifier 27h 🎀

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✨ SYNOPSIS ✨

No cap, here's the whole shape of it, verbatim, don't touch a single character:

struct nvme_voltage_measurement_log {
    __u8 vmgn;
    __u8 vma;
    __le16 vsi;
    __le32 vmlsz;
    __le16 nvmds;
    __le16 nvmde;
    __le16 svmtr;
    struct nvme_timestamp   svmts;
    __le16 cntlid;
    __le16 vlvss;
    __u8 rsvd26[6];
    __le16 ovol;
    __le16 ovc;
    __le16 ovlt;
    struct nvme_timestamp   ovts;
    __u8 iovpe;
    __le16 uvol;
    __le16 uvc;
    __le16 uvlt;
    struct nvme_timestamp   uvts;
    __u8 iuvpe;
    __u8 rsvd62[2];
    __le16 ivmd[];
};

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🦋 Members 🦋

Okay so this is the part where we go field by field, and honestly? Every one of them is iconic in its own way:

• vmgn — Voltage Measurement Generation Number 💫 it gets incremented every single time a Set Features command starts Voltage Measurements. Like a little counter that only goes up.
• vma — Voltage Measurement Attributes, peek at enum nvme_voltage_measurement_vma for the deets.
• vsi — Voltage Sensor Info, see enum nvme_voltage_measurement_vsi. Ngl though, this one is meaningless if the VMC bit is cleared to '0' in vma — so check your bits before you get attached 😭
• vmlsz — Voltage Measurement Log Size: how big this log page is, in bytes.
• nvmds — Number of Voltage Measurement Descriptors Supported: literally the max number of entries the Interval Voltage Measurement Descriptor list can hold.
• nvmde — Number of Voltage Measurement Descriptors Entries: how many entries are actually chillin' in ivmd right now.
• svmtr — Stop Voltage Measurement Time Remaining, in minutes, rounded up (generous queen behavior 🫶).
• svmts — Stop Voltage Measurement Timestamp: the exact time interval voltage measurements stopped being collected. See struct nvme_timestamp for the format.
• cntlid — Controller Identifier, the one associated with vsi, svmts, ovts, and uvts. One controller to bind them all 💅
• vlvss — Voltage Log Vendor Specific Size: size in bytes of the Vendor Specific field that comes right after ivmd.
• rsvd26 — Reserved. Not for you. Move along 🙈
• ovol — Overvoltage, see enum nvme_voltage_measurement_ovol.
• ovc — Overvoltage Count.
• ovlt — Overvoltage Log Threshold, measured in units of the Voltage Sensor Sample Scale.
• ovts — Overvoltage Timestamp. See struct nvme_timestamp. ⏰
• iovpe — Interval Overvoltage Percent Error, ranges from 0 to 100. And if it's 255? That means a value is not reported — it's giving "no data, no opinion" 💀
• uvol — Undervoltage, see enum nvme_voltage_measurement_uvol.
• uvc — Undervoltage Count.
• uvlt — Undervoltage Log Threshold, also in units of the Voltage Sensor Sample Scale.
• uvts — Undervoltage Timestamp. See struct nvme_timestamp. ⏰
• iuvpe — Interval Undervoltage Percent Error, 0 to 100 again. And again, 255 means a value is not reported.
• rsvd62 — Reserved. Same vibe as the other one: hands off 😌
• ivmd — Interval Voltage Measurement Descriptor list, see enum nvme_voltage_measurement_ivmd. And plot twist: it's followed by a Vendor Specific field that's vlvss bytes long — if vlvss is non-zero. Conditional queen 👑

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Lowkey important reminder bestie: this is a flexible array member situation at the end (ivmd[]), so the vendor-specific stuff just trails along after it. Don't go reading past what vmlsz tells you, okay? 🫶

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🌈 that's the whole page! 🌈

Written for the libnvme API Manual, this very page dropped in October 2026, star of the show struct nvme_voltage_measurement_log, living in section libnvme(9). Slay, bye 💖✨🎀