io_uring: remove IORING_CQE_F_MSG

This was introduced with the message ring opcode, but isn't strictly
required for the request itself. The sender can encode what is needed
in user_data, which is passed to the receiver. It's unclear if having
a separate flag that essentially says "This CQE did not originate from
an SQE on this ring" provides any real utility to applications. While
we can always re-introduce a flag to provide this information, we cannot
take it away at a later point in time.

Remove the flag while we still can, before it's in a released kernel.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: axboe

fs/io_uring.c

@@ -4474,8 +4474,7 @@ static int io_msg_ring(struct io_kiocb *req, unsigned int issue_flags)
 	target_ctx = req->file->private_data;
 
 	spin_lock(&target_ctx->completion_lock);
-	filled = io_fill_cqe_aux(target_ctx, msg->user_data, msg->len,
-					IORING_CQE_F_MSG);
+	filled = io_fill_cqe_aux(target_ctx, msg->user_data, msg->len, 0);
 	io_commit_cqring(target_ctx);
 	spin_unlock(&target_ctx->completion_lock);
 

include/uapi/linux/io_uring.h

@@ -201,11 +201,9 @@ struct io_uring_cqe {
  *
  * IORING_CQE_F_BUFFER	If set, the upper 16 bits are the buffer ID
  * IORING_CQE_F_MORE	If set, parent SQE will generate more CQE entries
- * IORING_CQE_F_MSG	If set, CQE was generated with IORING_OP_MSG_RING
  */
 #define IORING_CQE_F_BUFFER		(1U << 0)
 #define IORING_CQE_F_MORE		(1U << 1)
-#define IORING_CQE_F_MSG		(1U << 2)
 
 enum {
 	IORING_CQE_BUFFER_SHIFT		= 16,