pci_read_legacy_io(9)

💅 pci_read_legacy_io — like, the Kernel API Manual page for it ✨

okay bestie, so this is <pink>pci_read_legacy_io</pink> from the Kernel API Manual, and it's literally the function that reads byte(s) from legacy I/O port space. yes, that legacy I/O port space. we're going old school and it's kind of iconic 🎀

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✨ NAME ✨

pci_read_legacy_io — read byte(s) from legacy I/O port space 🫶

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🌸 SYNOPSIS 🌸

ssize_t pci_read_legacy_io (struct file *filp , struct kobject *kobj ,
const struct bin_attribute *bin_attr , char *buf , loff_t off , size_t
count );

like, that's the whole signature, no cap. six args, one return value of type ssize_t. slay 💅

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🦋 ARGUMENTS 🦋

one bullet per parameter because we respect ourselves:

• filp — the open sysfs file, fr fr. it's a struct file * and it's literally just sitting there being the file you opened 👑
• kobj — the kobject that corresponds to the file you're reading from. it's giving "who am I actually talking to" energy ✨
• bin_attr — the struct bin_attribute for this file. yes, that's the binary attribute struct, and yes, it's const 💜
• buf — the buffer where the results go. this is the destination, the main character, the place your bytes end up 🌈
• off — the offset into legacy I/O port space. like, where in the port space you're starting from 🎀
• count — the number of bytes to read. the vibe check on how much you want 🍓

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💖 DESCRIPTION 💖

okay so here's the tea: pci_read_legacy_io reads 1, 2, or 4 bytes from legacy I/O port space.

that's it. that's the whole thing. but — and this is the fun part — it does it using an arch specific callback routine, specifically pci_legacy_read. so it's not out here raw-dogging the port space itself, it's delegating to the architecture's own little helper. teamwork, honestly 🫶

literally only 1, 2, or 4 bytes. not 3. not 8. bestie, don't come at it with a weird size, that's not the move 💀

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🌟 SEE ALSO 🌟

the whole friend group, plus the kernel file they all live in:

• Kernel file ./drivers/pci/pci-sysfs.c — that's the source file, go read it, iykyk 📖
• pci_write_legacy_io(9) — the writing counterpart, the other half of the ship 💕
• pci_mmap_legacy_mem(9) — legacy memory, but mmap'd 🧚
• pci_mmap_legacy_io(9) — legacy I/O, but mmap'd 🌸
• pci_mmap_resource(9) — mmap a resource, iconic behaviour 🔥
• pci_write_rom(9) — write to ROM, careful with that one 🫶
• pci_read_rom(9) — read from ROM, the safer sibling ✨

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🎀 the cute sign-off 🎀

so this little beauty lives over in ./drivers/pci, and the docs are stamped October 2026 — like, future date, main character energy, we love to see it. and obviously it's all about pci_read_legacy_io(9), which is the page you just read. periodt 💅💖