io_uring: combine buffer lookup and import

Registered buffer are currently imported in two steps, first we lookup
a rsrc node and then use it to set up the iterator. The first part is
usually done at the prep stage, and import happens whenever it's needed.
As we want to defer binding to a node so that it works with linked
requests, combine both steps into a single helper.

Reviewed-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250224213116.3509093-6-kbusch@meta.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/rsrc.h

@@ -50,9 +50,9 @@ void io_free_rsrc_node(struct io_ring_ctx *ctx, struct io_rsrc_node *node);
 void io_rsrc_data_free(struct io_ring_ctx *ctx, struct io_rsrc_data *data);
 int io_rsrc_data_alloc(struct io_rsrc_data *data, unsigned nr);
 
-int io_import_fixed(int ddir, struct iov_iter *iter,
-			   struct io_mapped_ubuf *imu,
-			   u64 buf_addr, size_t len);
+int io_import_reg_buf(struct io_kiocb *req, struct iov_iter *iter,
+			u64 buf_addr, size_t len, int ddir,
+			unsigned issue_flags);
 
 int io_register_clone_buffers(struct io_ring_ctx *ctx, void __user *arg);
 int io_sqe_buffers_unregister(struct io_ring_ctx *ctx);