Re: [RFC PATCH 3/3] bpf: Add sk_lookup test to use ORIGDSTADDR cmsg.

[Philo Lu]

Hi Tiago,

On 2024/9/13 17:39, Tiago Lam wrote:
> This patch reuses the framework already in place for sk_lookup, allowing
> it now to send a reply from the server fd directly, instead of having to
> create a socket bound to the original destination address and reply from
> there. It does this by passing the source address and port from where to
> reply from in a IP_ORIGDSTADDR ancilliary message passed in sendmsg.
>
> Signed-off-by: Tiago Lam <tiagolam@xxxxxxxxxxxxxx>
> ---
>   tools/testing/selftests/bpf/prog_tests/sk_lookup.c | 70 +++++++++++++++-------
>   1 file changed, 48 insertions(+), 22 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/sk_lookup.c b/tools/testing/selftests/bpf/prog_tests/sk_lookup.c
> index ae87c00867ba..b99aff2e3976 100644
> --- a/tools/testing/selftests/bpf/prog_tests/sk_lookup.c
> +++ b/tools/testing/selftests/bpf/prog_tests/sk_lookup.c
> @@ -75,6 +75,7 @@ struct test {
>   	struct inet_addr listen_at;
>   	enum server accept_on;
>   	bool reuseport_has_conns; /* Add a connected socket to reuseport group */
> +	bool dont_bind_reply; /* Don't bind, send direct from server fd. */
>   };
>   
>   struct cb_opts {
> @@ -363,7 +364,7 @@ static void v4_to_v6(struct sockaddr_storage *ss)
>   	memset(&v6->sin6_addr.s6_addr[0], 0, 10);
>   }
>   
> -static int udp_recv_send(int server_fd)
> +static int udp_recv_send(int server_fd, bool dont_bind_reply)
>   {
>   	char cmsg_buf[CMSG_SPACE(sizeof(struct sockaddr_storage))];
>   	struct sockaddr_storage _src_addr = { 0 };
> @@ -415,26 +416,41 @@ static int udp_recv_send(int server_fd)
>   		v4_to_v6(dst_addr);
>   	}
>   
> -	/* Reply from original destination address. */
> -	fd = start_server_addr(SOCK_DGRAM, dst_addr, sizeof(*dst_addr), NULL);
> -	if (!ASSERT_OK_FD(fd, "start_server_addr")) {
> -		log_err("failed to create tx socket");
> -		return -1;
> -	}
> +	if (dont_bind_reply) {
> +		/* Reply directly from server fd, specifying the source address and/or
> +		 * port in struct msghdr.
> +		 */
> +		n = sendmsg(server_fd, &msg, 0);
> +		if (CHECK(n <= 0, "sendmsg", "failed\n")) {
> +			log_err("failed to send echo reply");
> +			return -1;
> +		}
> +	} else {
> +		/* Reply from original destination address. */
> +		fd = socket(dst_addr->ss_family, SOCK_DGRAM, 0);
> +		if (CHECK(fd < 0, "socket", "failed\n")) {
> +			log_err("failed to create tx socket");
> +			return -1;
> +		}
>   
Just curious, why not use start_server_addr() here like before?

> -	msg.msg_control = NULL;
> -	msg.msg_controllen = 0;
> -	n = sendmsg(fd, &msg, 0);
> -	if (CHECK(n <= 0, "sendmsg", "failed\n")) {
> -		log_err("failed to send echo reply");
> -		ret = -1;
> -		goto out;
> -	}
> +		ret = bind(fd, (struct sockaddr *)dst_addr, sizeof(*dst_addr));
> +		if (CHECK(ret, "bind", "failed\n")) {
> +			log_err("failed to bind tx socket");
> +			close(fd);
> +			return ret;
> +		}
>   
> -	ret = 0;
> -out:
> -	close(fd);
> -	return ret;
> +		msg.msg_control = NULL;
> +		msg.msg_controllen = 0;
> +		n = sendmsg(fd, &msg, 0);
> +		if (CHECK(n <= 0, "sendmsg", "failed\n")) {
> +			log_err("failed to send echo reply");
> +			close(fd);
> +			return -1;
> +		}
> +
> +		close(fd);
> +	}

nit: "return 0" missed.

>   }
>   

--
Philo