STRUCT MSI_MSG(9)

💖 struct msi_msg(9) 💖

okay so bestie, welcome to the Kernel API Manual — we're looking at struct msi_msg today and honestly? it's giving "small but mighty." ✨

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🌸 NAME 🌸

struct msi_msg — the representation of a MSI message 🎀

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🦋 SYNOPSIS 🦋

struct msi_msg {
    union {
      u32 address_lo;
      arch_msi_msg_addr_lo_t arch_addr_lo;
    };
    union {
      u32 address_hi;
      arch_msi_msg_addr_hi_t arch_addr_hi;
    };
    union {
      u32 data;
      arch_msi_msg_data_t arch_data;
    };
 };

look at her. three little unions, all anonymous, all iconic. 👑

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💅 Members 💅

so like. each of these blocks is an {unnamed_union} and it's just anonymous. yes really. no name, no problem. she's mysterious like that. 🙈

• address_lo — the low 32 bits of the msi message address. the little half. 🍓
• arch_addr_lo — the architecture specific shadow of address_lo. same vibe, different arch, iykyk.
• {unnamed_union} — anonymous. again. mystery queen behavior.
• address_hi — the high 32 bits of the msi message address — only used when the device supports it, so don't come for her if she's sitting there unused.
• arch_addr_hi — the architecture specific shadow of address_hi. matching set fr fr. 🫶
• {unnamed_union} — anonymous. third time's the charm bestie.
• data — the MSI message data, usually 16 bits. tiny but she's doing the work.
• arch_data — the architecture specific shadow of data. the arch-specific twin, slaying in the background. 💜

ngl the whole struct is basically real value + arch-specific shadow ×3, and that's the entire plot. no notes. 🔥

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🔥 SEE ALSO 🔥

Kernel file ./include/linux/msi.h — and the whole friend group:

• struct pci_msi_desc(9)
• union msi_domain_cookie(9)
• struct msi_desc_data(9)
• struct msi_desc(9)
• struct msi_dev_domain(9)
• msi_first_desc(9)
• msi_domain_for_each_desc(9)
• msi_for_each_desc(9)
• msi_msg_set_addr(9)
• msi_insert_msi_desc(9)
• msi_free_msi_descs_range(9)
• msi_free_msi_descs(9)
• struct msi_domain_ops(9)
• struct msi_domain_info(9)
• struct msi_domain_template(9)
• struct msi_parent_ops(9)

go read them, they all ate. 💀✨

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and that's the whole page bestie!! mwah 🫶 this one lives in ./include/linux and the date on it is October 2026 — so like, she's from the future, main character energy fr. 🌈⭐ bye babes!! 💖