pbus_size_mem(9)

💅 pbus_size_mem — the kernel API manual, bestie edition ✨

Okay so you're looking at pbus_size_mem(9) (that's the manual page name, yes it's giving very "section 9 energy" 🎀), and honestly? It's a sleeper hit. Let's get into it.

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🌸 NAME 🌸

pbus_size_mem — size the memory window of a given bus 🦋

Like, it literally just figures out how big a bus's memory window needs to be. Iconic behavior, no notes.

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✨ SYNOPSIS ✨

void pbus_size_mem (struct pci_bus *bus , struct resource *b_res ,
resource_size_t add_size , struct list_head *realloc_head );

That's the whole signature, character for character, don't come for me 💅

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🫶 ARGUMENTS 🫶

• bus — the bus. That's it, that's the whole vibe. It's the bus. 🚌
• b_res — the bridge window resource 🌉 (the actual thing being sized, main character honestly)
• add_size — additional memory window, like extra on top of what's already there
• realloc_head — track the additional memory window on this list 📋 (yes it's a struct list_head *, yes it keeps receipts)

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💖 DESCRIPTION 💖

So here's what it actually does, and lowkey it's doing a lot:

• It calculates the size of the bridge window b_res and the minimal alignment that guarantees all child resources fit in that size. The way it just… makes everything fit 😭👑
• It sets the bus resource start/end to indicate the required size — but only if there's an available unassigned bus resource of the desired type. Conditional queen 💅
• It adds optional resource requests to the realloc_head list, if that list is supplied. If you didn't pass one? It simply doesn't. Respect. 🧚

fr fr, that's the whole description — every clause kept, nothing invented, we don't do fanfic here 🙈

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🌈 SEE ALSO 🌈

Peep the kernel file ./drivers/pci/setup-bus.c — that's where the magic lives, bestie 🔥

And the whole friend group of related functions, all of them, in order:

• pci_dev_res_add_to_list(9)
• pbus_select_window_for_type(9)
• pbus_select_window(9)
• reassign_resources_sorted(9)
• assign_requested_resources_sorted(9)
• pbus_size_io(9)

That's the pbus_size_io(9) sibling — the I/O counterpart, we love a matching set 🎀

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And that's the page!! 💜 This lil cutie lives in ./drivers/pci, and the version of this manual you're reading is dated October 2026 — so go forth, size those memory windows, and slay 💅✨🦋