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

[lizetao <lizetao1@huawei.com>]

Hi,

> -----Original Message-----
> From: David Wei <dw@davidwei.uk>
> Sent: Saturday, February 22, 2025 4:52 AM
> To: io-uring@vger.kernel.org
> Cc: Jens Axboe <axboe@kernel.dk>; Pavel Begunkov <asml.silence@gmail.com>
> Subject: [PATCH v2 1/2] io_uring/zcrx: add single shot recvzc
> 
> 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 */

What is the difference between unlimited read length and IO_URING_F_MULTISHOT?
In what specific scenarios would unlimited read length be used?

> +	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;

It is not used.

>  	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
> 
> 

---
Li Zetao