dma_mmap_attrs(9)

📦 version 7.3.1, in nixpkgs unstable

💅 dma_mmap_attrs(9) — the Kernel API Manual, bestie edition 🎀

okay so real talk: this is a page from the Kernel API Manual, and it's literally about giving user space a peek at your DMA buffer. no cap, it's iconic.

✨ NAME ✨

dma_mmap_attrs — map a coherent DMA allocation into user space 🦋

so yeah, that's the whole vibe. coherent DMA allocation ➡️ user space. slay.

🌸 SYNOPSIS 🌸

int dma_mmap_attrs (struct device *dev , struct vm_area_struct *vma ,
void *cpu_addr , dma_addr_t dma_addr , size_t size , unsigned long attrs
);

not me writing out the whole signature, but like… you need it, so here it is, character for character 💖

👑 ARGUMENTS 👑

okay these are the glow-ups you gotta pass in. every single one matters, bestie:

  • dev — a valid struct device pointer. or, and this is the fun part, NULL for ISA and EISA-like devices 🙈 (yes, those old iconique ones)
  • vma — the vm_area_struct that describes the user mapping you're asking for. it's giving "here's what user space wants" ✨
  • cpu_addr — the kernel CPU-view address, and — important — it's the one returned from dma_alloc_attrs
  • dma_addr — the device-view address, also returned from dma_alloc_attrs. yes, it's a different address, no, that's not a typo 💀
  • size — size of the memory you originally requested in dma_alloc_attrs. not a new size, the original one, k?
  • attrs — the attributes of the mapping properties that you requested back in dma_alloc_attrs. keep them matching, iykyk 🫶

🔥 DESCRIPTION 🔥

so what does it actually do? it maps a coherent DMA buffer — one that was previously allocated by dma_alloc_attrs — into user space. that's it, that's the whole buffet 🌈

⚠️ THE BIG ONE, DO NOT SKIP THIS: the coherent DMA buffer must not be freed by the driver until the user space mapping has been released. like, fr fr. free it early and you're in for a bad time 😭 it's the main character rule of this whole page.

🧚 SEE ALSO 🧚

the friend group 🫶 — these all live in the kernel file ./kernel/dma/mapping.c:

✨ that's the page!! ✨ this little beauty ships out of ./kernel/dma, and the version date on it is October 2026 — so like, mark your calendars bestie 🎀💜 go map some memory, respectfully 💅

📦 where this page comes from