netdev - RE: [Patch bpf-next v8 11/16] udp: implement ->read

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Message-ID: <6065619aa26d1_938bb2085e@john-XPS-13-9370.notmuch>
Date:   Wed, 31 Mar 2021 23:00:58 -0700
From:   John Fastabend <john.fastabend@...il.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 v8 11/16] udp: implement ->read_sock() for
 sockmap

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.
> 
> Note, the return value of ->read_sock() is unused in
> sk_psock_verdict_data_ready(), and UDP still does not
> support splice() due to lack of ->splice_read(), so users
> can not reach udp_read_sock() directly.
> 
> 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>
> ---

Thanks this is easier to read IMO. One nit below.

Acked-by: John Fastabend <john.fastabend@...il.com>

[...]

>  
> +int udp_read_sock(struct sock *sk, read_descriptor_t *desc,
> +		  sk_read_actor_t recv_actor)
> +{
> +	int copied = 0;
> +
> +	while (1) {
> +		struct sk_buff *skb;
> +		int err, used;
> +
> +		skb = skb_recv_udp(sk, 0, 1, &err);
> +		if (!skb)
> +			return err;
> +		used = recv_actor(desc, skb, 0, skb->len);
> +		if (used <= 0) {
> +			if (!copied)
> +				copied = used;
> +			break;
> +		} else if (used <= skb->len) {
> +			copied += used;
> +		}

This 'else if' is always true if above is false right? Would be
impler and clearer IMO as,

               if (used <= 0) {
		        if (!copied)
				copied = used;
			break;
               }
               copied += used;

I don't see anyway for used to be great than  skb->len.

> +
> +		if (!desc->count)
> +			break;
> +	}
> +
> +	return copied;
> +}
> +EXPORT_SYMBOL(udp_read_sock);
> +