Re: [RFC v2 10/11] io_uring/rsrc: add dmabuf-backed buffer registeration

[Ming Lei <ming.lei@redhat.com>]

On Sun, Nov 23, 2025 at 10:51:30PM +0000, Pavel Begunkov wrote:
> Add an ability to register a dmabuf backed io_uring buffer. It also
> needs know which device to use for attachment, for that it takes
> target_fd and extracts the device through the new file op. Unlike normal
> buffers, it also retains the target file so that any imports from
> ineligible requests can be rejected in next patches.
> 
> Suggested-by: Vishal Verma <vishal1.verma@intel.com>
> Suggested-by: David Wei <dw@davidwei.uk>
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
>  io_uring/rsrc.c | 106 +++++++++++++++++++++++++++++++++++++++++++++++-
>  io_uring/rsrc.h |   1 +
>  2 files changed, 106 insertions(+), 1 deletion(-)
> 
> diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
> index 691f9645d04c..7dfebf459dd0 100644
> --- a/io_uring/rsrc.c
> +++ b/io_uring/rsrc.c
> @@ -10,6 +10,8 @@
>  #include <linux/compat.h>
>  #include <linux/io_uring.h>
>  #include <linux/io_uring/cmd.h>
> +#include <linux/dma-buf.h>
> +#include <linux/dma_token.h>
>  
>  #include <uapi/linux/io_uring.h>
>  
> @@ -802,6 +804,106 @@ bool io_check_coalesce_buffer(struct page **page_array, int nr_pages,
>  	return true;
>  }
>  
> +struct io_regbuf_dma {
> +	struct dma_token		*token;
> +	struct file			*target_file;
> +	struct dma_buf			*dmabuf;
> +};
> +
> +static void io_release_reg_dmabuf(void *priv)
> +{
> +	struct io_regbuf_dma *db = priv;
> +
> +	dma_token_release(db->token);
> +	dma_buf_put(db->dmabuf);
> +	fput(db->target_file);
> +	kfree(db);
> +}
> +
> +static struct io_rsrc_node *io_register_dmabuf(struct io_ring_ctx *ctx,
> +						struct io_uring_reg_buffer *rb,
> +						struct iovec *iov)
> +{
> +	struct dma_token_params params = {};
> +	struct io_rsrc_node *node = NULL;
> +	struct io_mapped_ubuf *imu = NULL;
> +	struct io_regbuf_dma *regbuf = NULL;
> +	struct file *target_file = NULL;
> +	struct dma_buf *dmabuf = NULL;
> +	struct dma_token *token;
> +	int ret;
> +
> +	if (iov->iov_base || iov->iov_len)
> +		return ERR_PTR(-EFAULT);
> +
> +	node = io_rsrc_node_alloc(ctx, IORING_RSRC_BUFFER);
> +	if (!node) {
> +		ret = -ENOMEM;
> +		goto err;
> +	}
> +
> +	imu = io_alloc_imu(ctx, 0);
> +	if (!imu) {
> +		ret = -ENOMEM;
> +		goto err;
> +	}
> +
> +	regbuf = kzalloc(sizeof(*regbuf), GFP_KERNEL);
> +	if (!regbuf) {
> +		ret = -ENOMEM;
> +		goto err;
> +	}
> +
> +	target_file = fget(rb->target_fd);
> +	if (!target_file) {
> +		ret = -EBADF;
> +		goto err;
> +	}
> +
> +	dmabuf = dma_buf_get(rb->dmabuf_fd);
> +	if (IS_ERR(dmabuf)) {
> +		ret = PTR_ERR(dmabuf);
> +		dmabuf = NULL;
> +		goto err;
> +	}
> +
> +	params.dmabuf = dmabuf;
> +	params.dir = DMA_BIDIRECTIONAL;
> +	token = dma_token_create(target_file, &params);
> +	if (IS_ERR(token)) {
> +		ret = PTR_ERR(token);
> +		goto err;
> +	}
> +

This way looks less flexible, for example, the same dma-buf may be used
on IOs to multiple disks, then it needs to be registered for each target
file.



Thanks,
Ming