libnvme(2)

💖 NAME 💖

struct nvme_passthru_cmd64 — the 64-bit nvme passthrough command structure 🦋

ok so bestie, welcome to section 2 of the libnvme API Manual — yes, the actual manual, manual name and all, and today's main character is a struct. A whole struct. And honestly? She deserves it. 💅

If you've ever wanted to just... tell an NVMe drive exactly what to do, no vibes-filtering, no fancy abstraction layer, no "the library will handle it" — that's what passthrough is. You hand the kernel a command basically as-is, and it goes straight to the controller. And this struct is the 64-bit version of that envelope. ✨

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✨ SYNOPSIS ✨

struct nvme_passthru_cmd64 {
    __u8 opcode;
    __u8 flags;
    __u16 rsvd1;
    __u32 nsid;
    __u32 cdw2;
    __u32 cdw3;
    __u64 metadata;
    __u64 addr;
    __u32 metadata_len;
    __u32 data_len;
    __u32 cdw10;
    __u32 cdw11;
    __u32 cdw12;
    __u32 cdw13;
    __u32 cdw14;
    __u32 cdw15;
    __u32 timeout_ms;
    __u32 rsvd2;
    __u64 result;
 };

look at her. so many __u32s. so many dwords. iconic. 🧚

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🎀 Members 🎀

okay bestie, let's go field by field, no skipping, I see you trying to scroll past cdw13 🙈

• opcode — the operation code. which command are we even doing? check enum nvme_io_opcodes and enum nvme_admin_opcodes, that's where the answers live. 👑
• flags — not supported. like, the field is there but it's meant for command flags (eg: SGL, FUSE) and it doesn't do that. don't @ it. 💀
• rsvd1 — reserved for future use. basically a little seat saved for a future era. 🎀
• nsid — Namespace Identifier, or a Fabrics type, depending on the situation. she contains multitudes. 🌸
• cdw2 — Command Dword 2, and there is no spec defined use for this one. it's just... hanging out. 🦋
• cdw3 — Command Dword 3, same situation, no spec defined use. her and cdw2 are a duo fr fr. 💜
• metadata — user space address to the metadata buffer. if you're not using it, it's NULL. periodt. ✨
• addr — user space address to the data buffer. also NULL if you're not using it. 💅
• metadata_len — Metadata buffer transfer length. how much metadata are we moving, bestie. 📏
• data_len — Data buffer transfer length. how much data are we moving. 📦
• cdw10 — Command Dword 10, and this one is command specific, so its meaning depends on opcode. iykyk. 🧚
• cdw11 — Command Dword 11, also command specific. 🔥
• cdw12 — Command Dword 12, command specific, still going. ⭐
• cdw13 — Command Dword 13, command specific, the one you tried to skip. I saw that. 👀
• cdw14 — Command Dword 14, command specific. 🌈
• cdw15 — Command Dword 15, command specific. and that's the whole dword lineup, slay. 🎉
• timeout_ms — if this is non-zero, it overrides the system default timeout, measured in milliseconds. non-zero = you're the boss now. ⏰
• rsvd2 — reserved for future use (and fills an implicit struct pad — yeah the paren never closes, that's how the source text is, and honestly? she's valid to me. 🫶)
• result — set on completion to the command's CQE DWORD 0-1 controller response. this is where you find out how it went. 💌

heads up bestie — flags being unsupported and rsvd1 / rsvd2 being reserved are not suggestions. leave reserved stuff alone and don't expect flags to do anything, no cap. 🚫

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and that's the whole struct, every single field, nothing skipped, because you deserve to know all of her 🥹

cute lil sign-off moment: this page came from the struct nvme_passthru_cmd64 entry in the libnvme(2) manual, and it's dated July 2026 — so yeah, she's from the future and she's still out here describing a 64-bit passthrough command. timeless. go forth and pass commands through, bestie 💖✨