dma_buf_begin_cpu_access(9)

📦 version 7.3.1, in nixpkgs unstable

💅 dma_buf_begin_cpu_access(9) — from the Kernel API Manual, bestie

Okay so real talk: this is a kernel API manual page, and the function it's about is dma_buf_begin_cpu_access(9). That's the whole vibe. Let's get into it ✨

🌸 NAME 🌸

dma_buf_begin_cpu_access — you must call this before you touch a dma_buf from the cpu while you're in kernel context, no cap. It calls begin_cpu_access so the exporter can do its little prep ritual. And heads up: coherency is only guaranteed inside the range you specified, for the access direction you specified. That's it. That's the deal 💅

✨ SYNOPSIS ✨

int dma_buf_begin_cpu_access (struct dma_buf *dmabuf , enum
dma_data_direction direction );

🫶 ARGUMENTS 🫶

  • dmabuf [in] — the buffer you're prepping for cpu access. your main character 🎀
  • direction [in] — which way the access is going. the direction of access, literally.

💖 DESCRIPTION 💖

So once your cpu access is done, the caller should call dma_buf_end_cpu_access. And listen — only when cpu access is bracketed by both of those calls is it guaranteed to be coherent with other DMA access. Both. Not one. Both. periodt 🫶

This function will also wait for any DMA transactions that are tracked through implicit synchronization in dma_buf.resv. Slay. But for DMA transactions with explicit synchronization, this function will only ensure cache coherency — that's it. Callers must ensure synchronization with those DMA transactions on their own. iykyk, that part's on you 🧚

Lowkey important: it can return negative error values, and it returns 0 on success. Check your return value bestie, don't just vibe past it 😭

🔥 SEE ALSO 🔥

Kernel file ./drivers/dma-buf/dma-buf.c, plus the whole friend group:

and that's the page, bestie 🦋 go forth and bracket your cpu access 💜

this gem lives in ./drivers/dma-buf, dated October 2026 — mwah, love that for us 💋

📦 where this page comes from