STRUCT PCI_MSI_DESC(9)

✨ struct pci_msi_desc(9) — the PCI/MSI tea ☕💅

okay so bestie, welcome to the kernel API manual (that's the manual name, iykyk 🫶) and today's main character is struct pci_msi_desc — literally the PCI/MSI specific MSI descriptor data. it's giving "small struct, big responsibilities" ✨

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🌸 NAME 🌸

struct pci_msi_desc — the PCI/MSI-specific MSI descriptor data, no cap 💖

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🎀 SYNOPSIS 🎀

struct pci_msi_desc {
    union {
      u32 msi_mask;
      u32 msix_ctrl;
    };
    struct {
      u8 is_msix         : 1;
      u8 multiple        : 3;
      u8 multi_cap       : 3;
      u8 can_mask        : 1;
      u8 is_64           : 1;
      u8 is_virtual      : 1;
      unsigned default_irq;
    } msi_attrib;
    union {
      u8 mask_pos;
      void __iomem *mask_base;
    };
 };

like, look at those bitfields. : 1 everywhere. it's giving "every bit is precious" 🌈 and honestly? obsessed. 🧚

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👑 Members 👑

not a struct member? it's a member bestie, there's a difference, and we're gonna go through every single one fr fr 🍓

• {unnamed_union} — anonymous 💀 yes that's literally what it says. it has no name. it simply is.
• msi_mask — [PCI MSI] MSI cached mask bits 🔥
• msix_ctrl — [PCI MSI-X] MSI-X cached per vector control bits, periodt ✨
• msi_attrib — [PCI MSI/X] compound struct of MSI/X attributes 🎀
• {unnamed_union} — anonymous again 😭 second mystery union, we love a recurring motif
• mask_pos — [PCI MSI] mask register position 💅
• mask_base — [PCI MSI-X] mask register base address 👑

ngl the two anonymous unions are iconic in a "i refuse to be named" kind of way. respect. 🫶

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🦋 SEE ALSO 🦋

the whole friend group shows up, and we're listing them all because nobody gets left on read 💜

Kernel file ./include/linux/msi.h, plus:

• struct msi_msg(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)

like that's a whole group chat and you're invited 🎉✨

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okay that's the whole page bestie, no notes 🎀 this one came out of ./include/linux, Kernel API Manual, dated October 2026 — mwah, stan, and go read msi.h 💖💅🌟