STRUCT VIRTIO_PCIDEV_MSG(9)

💖 struct virtio_pcidev_msg — the whole kernel-API-manual moment 💖

okay so bestie, this page is from the Kernel API Manual and it's all about struct virtio_pcidev_msg — literally the virtio PCI device operation vibe. yes, it's giving "tiny struct, big responsibilities" energy and we're gonna stan every single field. 🎀

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✨ SYNOPSIS ✨

struct virtio_pcidev_msg {
    __u8 op;
    __u8 bar;
    __u16 reserved;
    __u32 size;
    __u64 addr;
    __u8 data[];
 };

like, look at her. she's gorgeous. she's packed. she's got a flexible array member at the end and everything. 👑

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🌸 Members 🌸

okay so let's go field by field, no skips, no cap:

• op — the operation to do. literally the main character of this whole struct, she tells everyone else what's happening. ✨
• bar — the bar. and like, heads up bestie: this one's only there with BAR read/write messages. it doesn't show up to every party. 🎀
• reserved — reserved. that's it. that's the whole description. she's just there holding space, and honestly? iconic. 🫶
• size — the size of the read/write, in bytes. important unit note, don't forget the bytes. 📏
• addr — the address to read/write. where the magic goes down. 📍
• data — the data. normally it's size long, BUT — and this is the plot twist — it's just one byte for VIRTIO_PCIDEV_OP_MMIO_MEMSET. so like, read the op first, iykyk. 😭

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⭐ Note ⭐

lowkey crucial detail incoming: all the fields are in native (CPU) endian. HOWEVER — and this is the part people always miss — the data values will often be in little endian. go check the ops above for the receipts. 🔥

bestie please don't mix these up, the endianness switch-up is exactly the kind of thing that eats a whole afternoon and your entire will to live 💀

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🦋 SEE ALSO 🦋

• Kernel file ./include/uapi/linux/virtio_pcidev.h enum — the enum, go read it, she's right there
• virtio_pcidev_ops(9) — the ops page, your next stop, fr fr

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and that's the whole page bestie, you ate that 💅✨

mwah 💜 this cutie came from ./include/uapi/linux and is dated October 2026 — same title on the way out as on the way in: struct virtio_pcidev_msg(9). go be great, and may all your endianness be exactly what you expected 🧚🌈