linux-kernel - Re: [PATCH bpf-next v1 1/5] af_unix: add read

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Date:   Thu, 29 Jul 2021 10:37:37 +0200
From:   Jakub Sitnicki <jakub@...udflare.com>
To:     Jiang Wang <jiang.wang@...edance.com>
Cc:     netdev@...r.kernel.org, cong.wang@...edance.com,
        duanxiongchun@...edance.com, xieyongji@...edance.com,
        chaiwen.cc@...edance.com, "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Lorenz Bauer <lmb@...udflare.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>, Shuah Khan <shuah@...nel.org>,
        Johan Almbladh <johan.almbladh@...finetworks.com>,
        linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH bpf-next v1 1/5] af_unix: add read_sock for stream
 socket types

On Tue, Jul 27, 2021 at 02:12 AM CEST, Jiang Wang wrote:
> To support sockmap for af_unix stream type, implement
> read_sock, which is similar to the read_sock for unix
> dgram sockets.
>
> Signed-off-by: Jiang Wang <jiang.wang@...edance.com>
> Reviewed-by: Cong Wang <cong.wang@...edance.com>.
> ---
>  net/unix/af_unix.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index 89927678c..32eeb4a6a 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -672,6 +672,8 @@ static int unix_dgram_sendmsg(struct socket *, struct msghdr *, size_t);
>  static int unix_dgram_recvmsg(struct socket *, struct msghdr *, size_t, int);
>  static int unix_read_sock(struct sock *sk, read_descriptor_t *desc,
>  			  sk_read_actor_t recv_actor);
> +static int unix_stream_read_sock(struct sock *sk, read_descriptor_t *desc,
> +				 sk_read_actor_t recv_actor);
>  static int unix_dgram_connect(struct socket *, struct sockaddr *,
>  			      int, int);
>  static int unix_seqpacket_sendmsg(struct socket *, struct msghdr *, size_t);
> @@ -725,6 +727,7 @@ static const struct proto_ops unix_stream_ops = {
>  	.shutdown =	unix_shutdown,
>  	.sendmsg =	unix_stream_sendmsg,
>  	.recvmsg =	unix_stream_recvmsg,
> +	.read_sock =	unix_stream_read_sock,
>  	.mmap =		sock_no_mmap,
>  	.sendpage =	unix_stream_sendpage,
>  	.splice_read =	unix_stream_splice_read,
> @@ -2311,6 +2314,15 @@ struct unix_stream_read_state {
>  	unsigned int splice_flags;
>  };
>
> +static int unix_stream_read_sock(struct sock *sk, read_descriptor_t *desc,
> +				 sk_read_actor_t recv_actor)
> +{
> +	if (unlikely(sk->sk_state != TCP_ESTABLISHED))
> +		return -EINVAL;

tcp_read_sock returns -ENOTCONN if socket is not connected.

For the sake of being consistent, and in case we start propagating the
error up the call chain, I'd use the same error code.

> +
> +	return unix_read_sock(sk, desc, recv_actor);
> +}
> +
>  static int unix_stream_read_generic(struct unix_stream_read_state *state,
>  				    bool freezable)
>  {