netdev - Re: [Patch bpf-next v6 08/12] udp: implement ->read

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Date:   Tue, 23 Mar 2021 14:31:52 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     Cong Wang <xiyou.wangcong@...il.com>, <netdev@...r.kernel.org>
CC:     <bpf@...r.kernel.org>, <duanxiongchun@...edance.com>,
        <wangdongdong.6@...edance.com>, <jiang.wang@...edance.com>,
        Cong Wang <cong.wang@...edance.com>,
        John Fastabend <john.fastabend@...il.com>,
        "Daniel Borkmann" <daniel@...earbox.net>,
        Jakub Sitnicki <jakub@...udflare.com>,
        Lorenz Bauer <lmb@...udflare.com>
Subject: Re: [Patch bpf-next v6 08/12] udp: implement ->read_sock() for
 sockmap

On 2021/3/23 8:38, Cong Wang wrote:
> From: Cong Wang <cong.wang@...edance.com>
> 
> This is similar to tcp_read_sock(), except we do not need
> to worry about connections, we just need to retrieve skb
> from UDP receive queue.
> 
> Cc: John Fastabend <john.fastabend@...il.com>
> Cc: Daniel Borkmann <daniel@...earbox.net>
> Cc: Jakub Sitnicki <jakub@...udflare.com>
> Cc: Lorenz Bauer <lmb@...udflare.com>
> Signed-off-by: Cong Wang <cong.wang@...edance.com>
> ---
>  include/net/udp.h   |  2 ++
>  net/ipv4/af_inet.c  |  1 +
>  net/ipv4/udp.c      | 35 +++++++++++++++++++++++++++++++++++
>  net/ipv6/af_inet6.c |  1 +
>  4 files changed, 39 insertions(+)
> 
> diff --git a/include/net/udp.h b/include/net/udp.h
> index df7cc1edc200..347b62a753c3 100644
> --- a/include/net/udp.h
> +++ b/include/net/udp.h
> @@ -329,6 +329,8 @@ struct sock *__udp6_lib_lookup(struct net *net,
>  			       struct sk_buff *skb);
>  struct sock *udp6_lib_lookup_skb(const struct sk_buff *skb,
>  				 __be16 sport, __be16 dport);
> +int udp_read_sock(struct sock *sk, read_descriptor_t *desc,
> +		  sk_read_actor_t recv_actor);
>  
>  /* UDP uses skb->dev_scratch to cache as much information as possible and avoid
>   * possibly multiple cache miss on dequeue()
> diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
> index 1355e6c0d567..f17870ee558b 100644
> --- a/net/ipv4/af_inet.c
> +++ b/net/ipv4/af_inet.c
> @@ -1070,6 +1070,7 @@ const struct proto_ops inet_dgram_ops = {
>  	.setsockopt	   = sock_common_setsockopt,
>  	.getsockopt	   = sock_common_getsockopt,
>  	.sendmsg	   = inet_sendmsg,
> +	.read_sock	   = udp_read_sock,
>  	.recvmsg	   = inet_recvmsg,
>  	.mmap		   = sock_no_mmap,
>  	.sendpage	   = inet_sendpage,
> diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> index 38952aaee3a1..a0adee3b1af4 100644
> --- a/net/ipv4/udp.c
> +++ b/net/ipv4/udp.c
> @@ -1782,6 +1782,41 @@ struct sk_buff *__skb_recv_udp(struct sock *sk, unsigned int flags,
>  }
>  EXPORT_SYMBOL(__skb_recv_udp);
>  
> +int udp_read_sock(struct sock *sk, read_descriptor_t *desc,
> +		  sk_read_actor_t recv_actor)
> +{
> +	int copied = 0;
> +
> +	while (1) {
> +		int offset = 0, err;
> +		struct sk_buff *skb;
> +
> +		skb = __skb_recv_udp(sk, 0, 1, &offset, &err);
> +		if (!skb)
> +			break;

Does above error handling need the below additional handling?
It seems __skb_recv_udp() will return the error by parameter "err",
if "copied == 0", does it need to return the error?

if (!skb) {
	if (!copied)
		copied = err;

	break;
}

> +		if (offset < skb->len) {
> +			int used;
> +			size_t len;
> +
> +			len = skb->len - offset;
> +			used = recv_actor(desc, skb, offset, len);
> +			if (used <= 0) {
> +				if (!copied)
> +					copied = used;
> +				break;

As here it seems handling the "copied == 0" error case.

> +			} else if (used <= len) {
> +				copied += used;
> +				offset += used;
> +			}
> +		}
> +		if (!desc->count)
> +			break;
> +	}
> +
> +	return copied;
> +}
> +EXPORT_SYMBOL(udp_read_sock);
> +
>  /*
>   * 	This should be easy, if there is something there we
>   * 	return it, otherwise we block.
> diff --git a/net/ipv6/af_inet6.c b/net/ipv6/af_inet6.c
> index 802f5111805a..71de739b4a9e 100644
> --- a/net/ipv6/af_inet6.c
> +++ b/net/ipv6/af_inet6.c
> @@ -714,6 +714,7 @@ const struct proto_ops inet6_dgram_ops = {
>  	.getsockopt	   = sock_common_getsockopt,	/* ok		*/
>  	.sendmsg	   = inet6_sendmsg,		/* retpoline's sake */
>  	.recvmsg	   = inet6_recvmsg,		/* retpoline's sake */
> +	.read_sock	   = udp_read_sock,
>  	.mmap		   = sock_no_mmap,
>  	.sendpage	   = sock_no_sendpage,
>  	.set_peek_off	   = sk_set_peek_off,
>