[RFC 2/2] io_uring/net: allow to override notification tag

[Pavel Begunkov <asml.silence@gmail.com>]

Considering limited amount of slots some users struggle with
registration time notification tag assignment as it's hard to manage
notifications using sequence numbers. Add a simple feature that copies
sqe->user_data of a send(+flush) request into the notification CQE it
flushes (and only when it's flushes).

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 include/uapi/linux/io_uring.h | 4 ++++
 io_uring/net.c                | 6 +++++-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 20368394870e..91e7944c9c78 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -280,11 +280,15 @@ enum io_uring_op {
  *
  * IORING_RECVSEND_NOTIF_FLUSH	Flush a notification after a successful
  *				successful. Only for zerocopy sends.
+ *
+ * IORING_RECVSEND_NOTIF_COPY_TAG Copy request's user_data into the notification
+ *				  completion even if it's flushed.
  */
 #define IORING_RECVSEND_POLL_FIRST	(1U << 0)
 #define IORING_RECV_MULTISHOT		(1U << 1)
 #define IORING_RECVSEND_FIXED_BUF	(1U << 2)
 #define IORING_RECVSEND_NOTIF_FLUSH	(1U << 3)
+#define IORING_RECVSEND_NOTIF_COPY_TAG	(1U << 4)
 
 /* cqe->res mask for extracting the notification sequence number */
 #define IORING_NOTIF_SEQ_MASK		0xFFFFU
diff --git a/io_uring/net.c b/io_uring/net.c
index bd3fad9536ef..4d271a269979 100644
--- a/io_uring/net.c
+++ b/io_uring/net.c
@@ -858,7 +858,9 @@ int io_sendzc_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 
 	zc->flags = READ_ONCE(sqe->ioprio);
 	if (zc->flags & ~(IORING_RECVSEND_POLL_FIRST |
-			  IORING_RECVSEND_FIXED_BUF | IORING_RECVSEND_NOTIF_FLUSH))
+			  IORING_RECVSEND_FIXED_BUF |
+			  IORING_RECVSEND_NOTIF_FLUSH |
+			  IORING_RECVSEND_NOTIF_COPY_TAG))
 		return -EINVAL;
 	if (zc->flags & IORING_RECVSEND_FIXED_BUF) {
 		unsigned idx = READ_ONCE(sqe->buf_index);
@@ -1024,6 +1026,8 @@ int io_sendzc(struct io_kiocb *req, unsigned int issue_flags)
 		if (ret == -ERESTARTSYS)
 			ret = -EINTR;
 	} else if (zc->flags & IORING_RECVSEND_NOTIF_FLUSH) {
+		if (zc->flags & IORING_RECVSEND_NOTIF_COPY_TAG)
+			notif->cqe.user_data = req->cqe.user_data;
 		io_notif_slot_flush_submit(notif_slot, 0);
 	}
 
-- 
2.37.0