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

[Pavel Begunkov <asml.silence@gmail.com>]

On 2/5/26 03:12, Ming Lei wrote:
> 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,
>    ...)

Yes, those should be possible to do, IIRC Christoph mentioned it
as well while asking to change the design of v1. The
implementation will need to forward registration down and create
a dma-buf attachment for each device.

-- 
Pavel Begunkov