UNION MSI_DOMAIN_COOKIE(9)

💅 union msi_domain_cookie(9) — she's from the Kernel API Manual 💅

Okay bestie, welcome to the group chat for union msi_domain_cookie(9) from the Kernel API Manual. This page is short, iconic, and a little mysterious — and yes, the mystery is the point. 🎀

🎀 NAME 🎀

union msi_domain_cookie — Opaque MSI domain specific data. That's it, that's the name. She's opaque, she's MSI-domain-specific, she's data. Periodt. 💅

✨ SYNOPSIS ✨

Here's the exact struct shape, bestie — no cap, this is the whole vibe:

       union msi_domain_cookie {
           u64 value;
           void *ptr;
           void __iomem *iobase;
        };

👯 Members 👯

• value — the u64 value store. Literally a store for a u64 value, sitting right there in the union. 💖
• ptr — Pointer to domain specific data. A pointer bestie with domain-specific data on the other end. 🫶
• iobase — Domain specific IOmem pointer. Yep, the domain-specific I/O memory pointer. ✨

🌸 Description 🌸

The content of this data is implementation defined, bestie — the implementation decides what goes in there. It's used by the MSI domain to store domain specific information which is requried for interrupt chip callbacks. (Yes, the manpage really says requried; I'm keeping the lore, not fixing the spelling. 😭)

🦋 SEE ALSO 🦋

• Kernel file: ./include/linux/msi.h
• struct msi_msg(9)
• struct pci_msi_desc(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)

xoxo, bestie — this one's from ./include/linux, dated October 2026. 💖🌷✨