Re: [PATCH v3 00/10] Add dmabuf read/write via io_uring

Ming Lei
2026-05-04T15:30:16Z

On Wed, Apr 29, 2026 at 04:25:46PM +0100, Pavel Begunkov wrote:
> The patch set allows to register a dmabuf to an io_uring instance for
> a specified file and use it with io_uring read / write requests. The
> infrastructure is not tied to io_uring and there could be more users
> in the future. A similar idea was attempted some years ago by Keith [1],
> from where I borrowed a good number of changes, and later was brough up
> by Tushar and Vishal from Intel.
>
> It's an opt-in feature for files, and they need to implement a new
> file operation to use it. Only NVMe block devices are supported in this
> series. The user API is built on top of io_uring's "registered buffers",
> where a dmabuf is registered in a special way, but after it can be used
> as any other "registered buffer" with IORING_OP_{READ,WRITE}_FIXED
> requests. It's created via a new file operation and the resulted map is
> then passed through the I/O stack in a new iterator type. There is some
> additional infrastructure to bind it all, which also counts requests
> using a dmabuf map and managing lifetimes, which is used to implement
> map invalidation.
>
> It was tested for GPU <-> NVMe transfers. Also, as it maintains a
> long-term dma mapping, it helps with the IOMMU cost. The numbers
> below are for udmabuf reads previously run by Anuj for different
> IOMMU modes:

Plain registered buffer is long-live too, which raises question: does this
framework need to take it into account from beginning?

BTW, inspired by this approach, I adds similar feature to ublk via UBLK_IO_F_SHMEM_ZC
which can maintain long-term vfio dma mapping over registered user-place aligned buffer.

Thanks,
Ming