[PATCH v2 1/2] io_uring/zcrx: add single shot recvzc

[David Wei <dw@davidwei.uk>]

Currently only multishot recvzc requests are supported, but sometimes
there is a need to do a single recv e.g. peeking at some data in the
socket. Add single shot recvzc requests where IORING_RECV_MULTISHOT is
_not_ set and the sqe->len field is set to the number of bytes to read
N.

There could be multiple completions containing data, like the multishot
case, since N bytes could be split across multiple frags. This is
followed by a final completion with res and cflags both set to 0 that
indicate the completion of the request, or a -res that indicate an
error.

Signed-off-by: David Wei <dw@davidwei.uk>
---
 io_uring/net.c  | 19 +++++++++++++++++--
 io_uring/zcrx.c | 17 ++++++++++++-----
 io_uring/zcrx.h |  2 +-
 3 files changed, 30 insertions(+), 8 deletions(-)

diff --git a/io_uring/net.c b/io_uring/net.c
index 000dc70d08d0..cae34a24266c 100644
--- a/io_uring/net.c
+++ b/io_uring/net.c
@@ -94,6 +94,7 @@ struct io_recvzc {
 	struct file			*file;
 	unsigned			msg_flags;
 	u16				flags;
+	u32				len;
 	struct io_zcrx_ifq		*ifq;
 };
 
@@ -1241,7 +1242,7 @@ int io_recvzc_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	unsigned ifq_idx;
 
 	if (unlikely(sqe->file_index || sqe->addr2 || sqe->addr ||
-		     sqe->len || sqe->addr3))
+		     sqe->addr3))
 		return -EINVAL;
 
 	ifq_idx = READ_ONCE(sqe->zcrx_ifq_idx);
@@ -1250,6 +1251,12 @@ int io_recvzc_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	zc->ifq = req->ctx->ifq;
 	if (!zc->ifq)
 		return -EINVAL;
+	zc->len = READ_ONCE(sqe->len);
+	if (zc->len == UINT_MAX)
+		return -EINVAL;
+	/* UINT_MAX means no limit on readlen */
+	if (!zc->len)
+		zc->len = UINT_MAX;
 
 	zc->flags = READ_ONCE(sqe->ioprio);
 	zc->msg_flags = READ_ONCE(sqe->msg_flags);
@@ -1269,6 +1276,7 @@ int io_recvzc_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 int io_recvzc(struct io_kiocb *req, unsigned int issue_flags)
 {
 	struct io_recvzc *zc = io_kiocb_to_cmd(req, struct io_recvzc);
+	bool limit = zc->len != UINT_MAX;
 	struct socket *sock;
 	int ret;
 
@@ -1281,7 +1289,7 @@ int io_recvzc(struct io_kiocb *req, unsigned int issue_flags)
 		return -ENOTSOCK;
 
 	ret = io_zcrx_recv(req, zc->ifq, sock, zc->msg_flags | MSG_DONTWAIT,
-			   issue_flags);
+			   issue_flags, &zc->len);
 	if (unlikely(ret <= 0) && ret != -EAGAIN) {
 		if (ret == -ERESTARTSYS)
 			ret = -EINTR;
@@ -1296,6 +1304,13 @@ int io_recvzc(struct io_kiocb *req, unsigned int issue_flags)
 		return IOU_OK;
 	}
 
+	if (zc->len == 0) {
+		io_req_set_res(req, 0, 0);
+
+		if (issue_flags & IO_URING_F_MULTISHOT)
+			return IOU_STOP_MULTISHOT;
+		return IOU_OK;
+	}
 	if (issue_flags & IO_URING_F_MULTISHOT)
 		return IOU_ISSUE_SKIP_COMPLETE;
 	return -EAGAIN;
diff --git a/io_uring/zcrx.c b/io_uring/zcrx.c
index f2d326e18e67..74bca4e471bc 100644
--- a/io_uring/zcrx.c
+++ b/io_uring/zcrx.c
@@ -817,6 +817,7 @@ io_zcrx_recv_skb(read_descriptor_t *desc, struct sk_buff *skb,
 	int i, copy, end, off;
 	int ret = 0;
 
+	len = min_t(size_t, len, desc->count);
 	if (unlikely(args->nr_skbs++ > IO_SKBS_PER_CALL_LIMIT))
 		return -EAGAIN;
 
@@ -894,26 +895,32 @@ io_zcrx_recv_skb(read_descriptor_t *desc, struct sk_buff *skb,
 out:
 	if (offset == start_off)
 		return ret;
+	if (desc->count != UINT_MAX)
+		desc->count -= (offset - start_off);
 	return offset - start_off;
 }
 
 static int io_zcrx_tcp_recvmsg(struct io_kiocb *req, struct io_zcrx_ifq *ifq,
 				struct sock *sk, int flags,
-				unsigned issue_flags)
+				unsigned issue_flags, unsigned int *outlen)
 {
+	unsigned int len = *outlen;
+	bool limit = len != UINT_MAX;
 	struct io_zcrx_args args = {
 		.req = req,
 		.ifq = ifq,
 		.sock = sk->sk_socket,
 	};
 	read_descriptor_t rd_desc = {
-		.count = 1,
+		.count = len,
 		.arg.data = &args,
 	};
 	int ret;
 
 	lock_sock(sk);
 	ret = tcp_read_sock(sk, &rd_desc, io_zcrx_recv_skb);
+	if (limit && ret)
+		*outlen = len - ret;
 	if (ret <= 0) {
 		if (ret < 0 || sock_flag(sk, SOCK_DONE))
 			goto out;
@@ -930,7 +937,7 @@ static int io_zcrx_tcp_recvmsg(struct io_kiocb *req, struct io_zcrx_ifq *ifq,
 		ret = IOU_REQUEUE;
 	} else if (sock_flag(sk, SOCK_DONE)) {
 		/* Make it to retry until it finally gets 0. */
-		if (issue_flags & IO_URING_F_MULTISHOT)
+		if (!limit && (issue_flags & IO_URING_F_MULTISHOT))
 			ret = IOU_REQUEUE;
 		else
 			ret = -EAGAIN;
@@ -942,7 +949,7 @@ static int io_zcrx_tcp_recvmsg(struct io_kiocb *req, struct io_zcrx_ifq *ifq,
 
 int io_zcrx_recv(struct io_kiocb *req, struct io_zcrx_ifq *ifq,
 		 struct socket *sock, unsigned int flags,
-		 unsigned issue_flags)
+		 unsigned issue_flags, unsigned int *len)
 {
 	struct sock *sk = sock->sk;
 	const struct proto *prot = READ_ONCE(sk->sk_prot);
@@ -951,5 +958,5 @@ int io_zcrx_recv(struct io_kiocb *req, struct io_zcrx_ifq *ifq,
 		return -EPROTONOSUPPORT;
 
 	sock_rps_record_flow(sk);
-	return io_zcrx_tcp_recvmsg(req, ifq, sk, flags, issue_flags);
+	return io_zcrx_tcp_recvmsg(req, ifq, sk, flags, issue_flags, len);
 }
diff --git a/io_uring/zcrx.h b/io_uring/zcrx.h
index a16bdd921f03..1b4042dc48e2 100644
--- a/io_uring/zcrx.h
+++ b/io_uring/zcrx.h
@@ -46,7 +46,7 @@ void io_unregister_zcrx_ifqs(struct io_ring_ctx *ctx);
 void io_shutdown_zcrx_ifqs(struct io_ring_ctx *ctx);
 int io_zcrx_recv(struct io_kiocb *req, struct io_zcrx_ifq *ifq,
 		 struct socket *sock, unsigned int flags,
-		 unsigned issue_flags);
+		 unsigned issue_flags, unsigned int *len);
 #else
 static inline int io_register_zcrx_ifq(struct io_ring_ctx *ctx,
 					struct io_uring_zcrx_ifq_reg __user *arg)
-- 
2.43.5