libnvme_read_regs(9)

💅 libnvme_read_regs — read the controller registers of a PCIe controller

okay so bestie, this is straight out of the libnvme API manual (section 9, we're fancy), and honestly? it's a little baddie. let's get into it 💖

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✨ SYNOPSIS ✨

int libnvme_read_regs (struct libnvme_transport_handle *hdl , __u32
offset , void *buf , __u32 len );

like yes, four whole arguments, she's serving signature 🎀

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🌸 ARGUMENTS 🌸

• hdl — your transport handle. the main character of this whole operation 🫶
• offset — where the first register starts, in bytes. not register indices, bestie, bytes 💀
• buf — the buffer where the register values get stashed. this is where the goods go 🎁
• len — how many bytes we're reading. keep it a multiple of 4, i'm begging 🙏

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🦋 DESCRIPTION 🦋

okay so what does she actually do? she copies the register range [offset, offset + len) of the controller into buf, and she does it using 32-bit MMIO reads. periodt. 🔥

the register values land in little-endian byte order, exactly as they appear in the register map — no sneaky byte-swapping, no "not me" moments, just faithful vibes 💜

now the rules, and these are non-negotiable lowkey:

• offset and len must be multiples of 4 (fr fr, no exceptions)
• the range must be within the first 4 KiB of the register map 🚧

⚠️ and listen — this should only be sent to controller handles, not to namespaces. sending it to a namespace is not the vibe, bestie. don't do it 🙈

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🍓 RETURN 🍓

• 0 on success, slay ✨
• a negative error code otherwise 😭
• specifically, -ENOTSUP means the transport has no memory-mapped registers — ie. that whole feature simply isn't there, and she's telling you so 💀

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that's the whole page, no cap 🧚 this one's from the libnvme API manual and it's dated October 2026, tagged libnvme_read_regs / libnvme_read_regs(9) — so go forth, read those registers, and remember: multiples of 4, first 4 KiB, controllers only. mwah 💅🌈👑