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

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