netdev - RE: [PATCH bpf-next v5 03/11] af_unix: implement ->read

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Date:   Mon, 12 Jul 2021 10:04:58 -0700
From:   John Fastabend <john.fastabend@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>, netdev@...r.kernel.org
Cc:     bpf@...r.kernel.org, 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 v5 03/11] af_unix: implement ->read_sock() for
 sockmap

Cong Wang wrote:
> From: Cong Wang <cong.wang@...edance.com>
> 
> Implement ->read_sock() for AF_UNIX datagram socket, it is
> pretty much similar to udp_read_sock().
> 
> 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>
> ---

[...]

> +static int unix_read_sock(struct sock *sk, read_descriptor_t *desc,
> +			  sk_read_actor_t recv_actor)
> +{
> +	int copied = 0;
> +
> +	while (1) {
> +		struct unix_sock *u = unix_sk(sk);
> +		struct sk_buff *skb;
> +		int used, err;
> +
> +		mutex_lock(&u->iolock);
> +		skb = skb_recv_datagram(sk, 0, 1, &err);
> +		mutex_unlock(&u->iolock);
> +		if (!skb)
> +			return err;
> +
> +		used = recv_actor(desc, skb, 0, skb->len);
> +		if (used <= 0) {
> +			if (!copied)
> +				copied = used;
> +			kfree_skb(skb);

Is it OK to drop a unix dgram? I think the sockets likely wouldn't
expect this?

Anyways I'll have a proposed fix for TCP side shortly. And we can
extend it here as well if needed.

> +			break;
> +		} else if (used <= skb->len) {
> +			copied += used;
> +		}
> +
> +		kfree_skb(skb);
> +		if (!desc->count)
> +			break;
> +	}
> +
> +	return copied;
> +}
> +
>  /*
>   *	Sleep until more data has arrived. But check for races..
>   */
> -- 
> 2.27.0
>