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Date: Thu, 4 Apr 2024 18:17:41 -0400
From: Oliver Crumrine <ozlinuxc@gmail.com>
To: axboe@kernel.dk, asml.silence@gmail.com, davem@davemloft.net, 
	edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, shuah@kernel.org, 
	leitao@debian.org
Cc: io-uring@vger.kernel.org, netdev@vger.kernel.org, 
	linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH 1/3] io_uring: Add REQ_F_CQE_SKIP support for io_uring
 zerocopy
Message-ID: <b1a047a1b2d55c1c245a78ca9772c31a9b3ceb12.1712268605.git.ozlinuxc@gmail.com>
References: <cover.1712268605.git.ozlinuxc@gmail.com>
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In-Reply-To: <cover.1712268605.git.ozlinuxc@gmail.com>

In his patch to enable zerocopy networking for io_uring, Pavel Begunkov
specifically disabled REQ_F_CQE_SKIP, as (at least from my
understanding) the userspace program wouldn't receive the
IORING_CQE_F_MORE flag in the result value.

To fix this, instead of keeping track of how many CQEs have been
received, and subtracting notifs from that, programs can keep track of
how many SQEs they have issued, and if a CQE is returned with an error,
they can simply subtract from how many notifs they expect to receive.

Signed-off-by: Oliver Crumrine <ozlinuxc@gmail.com>
---
 io_uring/net.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/io_uring/net.c b/io_uring/net.c
index 1e7665ff6ef7..822f49809b68 100644
--- a/io_uring/net.c
+++ b/io_uring/net.c
@@ -1044,9 +1044,6 @@ int io_send_zc_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 
 	if (unlikely(READ_ONCE(sqe->__pad2[0]) || READ_ONCE(sqe->addr3)))
 		return -EINVAL;
-	/* we don't support IOSQE_CQE_SKIP_SUCCESS just yet */
-	if (req->flags & REQ_F_CQE_SKIP)
-		return -EINVAL;
 
 	notif = zc->notif = io_alloc_notif(ctx);
 	if (!notif)
@@ -1342,7 +1339,8 @@ void io_sendrecv_fail(struct io_kiocb *req)
 		req->cqe.res = sr->done_io;
 
 	if ((req->flags & REQ_F_NEED_CLEANUP) &&
-	    (req->opcode == IORING_OP_SEND_ZC || req->opcode == IORING_OP_SENDMSG_ZC))
+	    (req->opcode == IORING_OP_SEND_ZC || req->opcode == IORING_OP_SENDMSG_ZC) &&
+	    !(req->flags & REQ_F_CQE_SKIP))
 		req->cqe.flags |= IORING_CQE_F_MORE;
 }
 
-- 
2.44.0