[LSF/MM/BPF TOPIC] dmabuf backed read/write

[Ming Lei]

On Tue, Feb 03, 2026 at 02:29:55PM +0000, Pavel Begunkov wrote:
> Good day everyone,
> 
> dma-buf is a powerful abstraction for managing buffers and DMA mappings,
> and there is growing interest in extending it to the read/write path to
> enable device-to-device transfers without bouncing data through system
> memory. I was encouraged to submit it to LSF/MM/BPF as that might be
> useful to mull over details and what capabilities and features people
> may need.
> 
> The proposal consists of two parts. The first is a small in-kernel
> framework that allows a dma-buf to be registered against a given file
> and returns an object representing a DMA mapping. The actual mapping
> creation is delegated to the target subsystem (e.g. NVMe). This
> abstraction centralises request accounting, mapping management, dynamic
> recreation, etc. The resulting mapping object is passed through the I/O
> stack via a new iov_iter type.
> 
> As for the user API, a dma-buf is installed as an io_uring registered
> buffer for a specific file. Once registered, the buffer can be used by
> read / write io_uring requests as normal. io_uring will enforce that the
> buffer is only used with "compatible files", which is for now restricted
> to the target registration file, but will be expanded in the future.
> Notably, io_uring is a consumer of the framework rather than a
> dependency, and the infrastructure can be reused.

I am interested in this topic.

Given dma-buf is inherently designed for sharing, I hope the io-uring
interface can be generic for covering:

- read/write with same dma-buf can be submitted to multiple devices

- read/write with dma-buf can cross stackable devices(device mapper, raid,
  ...)


Thanks,
Ming