Add io_uring_cmd_get_buffer_info() to fetch buffer information that will
be necessary for constructing an iov iter for it.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
---
 include/linux/io_uring/cmd.h |  2 ++
 io_uring/rsrc.c              | 21 +++++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/include/linux/io_uring/cmd.h b/include/linux/io_uring/cmd.h
index 7509025b4071..a92e810f37f9 100644
--- a/include/linux/io_uring/cmd.h
+++ b/include/linux/io_uring/cmd.h
@@ -177,4 +177,6 @@ int io_buffer_register_bvec(struct io_uring_cmd *cmd, struct request *rq,
 int io_buffer_unregister_bvec(struct io_uring_cmd *cmd, unsigned int index,
 			      unsigned int issue_flags);
 
+int io_uring_cmd_get_buffer_info(struct io_uring_cmd *cmd, u64 *ubuf,
+				 unsigned int *len);
 #endif /* _LINUX_IO_URING_CMD_H */
diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
index d787c16dc1c3..8554cdad8abc 100644
--- a/io_uring/rsrc.c
+++ b/io_uring/rsrc.c
@@ -1569,3 +1569,24 @@ int io_prep_reg_iovec(struct io_kiocb *req, struct iou_vec *iv,
 	req->flags |= REQ_F_IMPORT_BUFFER;
 	return 0;
 }
+
+int io_uring_cmd_get_buffer_info(struct io_uring_cmd *cmd, u64 *ubuf,
+				 unsigned int *len)
+{
+	struct io_ring_ctx *ctx = cmd_to_io_kiocb(cmd)->ctx;
+	struct io_rsrc_data *data = &ctx->buf_table;
+	struct io_mapped_ubuf *imu;
+	unsigned int buf_index;
+
+	if (!data->nr)
+		return -EINVAL;
+
+	buf_index = cmd->sqe->buf_index;
+	imu = data->nodes[buf_index]->buf;
+
+	*ubuf = imu->ubuf;
+	*len = imu->len;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(io_uring_cmd_get_buffer_info);
-- 
2.47.3