Subject: Re: [PATCH bpf v7 11/13] bpf: sockmap, test shutdown() correctly exits epoll and recv()=0

From: Jakub Sitnicki <[email-masked]>
Date: Mon, 08 May 2023 13:04:58 +0200

On Tue, May 02, 2023 at 08:51 AM -07, John Fastabend wrote:
> When session gracefully shutdowns epoll needs to wake up and any recv()
> readers should return 0 not the -EAGAIN they previously returned.
>
> Note we use epoll instead of select to test the epoll wake on shutdown
> event as well.
>
> Signed-off-by: John Fastabend <[email-masked]>
> ---
>  .../selftests/bpf/prog_tests/sockmap_basic.c  | 68 +++++++++++++++++++
>  .../bpf/progs/test_sockmap_pass_prog.c        | 32 +++++++++
>  2 files changed, 100 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/progs/test_sockmap_pass_prog.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c b/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c
> index 0ce25a967481..f9f611618e45 100644
> --- a/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c
> +++ b/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c
> @@ -2,6 +2,7 @@
>  // Copyright (c) 2020 Cloudflare
>  #include <error.h>
>  #include <netinet/tcp.h>
> +#include <sys/epoll.h>
>  
>  #include "test_progs.h"
>  #include "test_skmsg_load_helpers.skel.h"
> @@ -9,8 +10,11 @@
>  #include "test_sockmap_invalid_update.skel.h"
>  #include "test_sockmap_skb_verdict_attach.skel.h"
>  #include "test_sockmap_progs_query.skel.h"
> +#include "test_sockmap_pass_prog.skel.h"
>  #include "bpf_iter_sockmap.skel.h"
>  
> +#include "sockmap_helpers.h"
> +
>  #define TCP_REPAIR		19	/* TCP sock is under repair right now */
>  
>  #define TCP_REPAIR_ON		1
> @@ -350,6 +354,68 @@ static void test_sockmap_progs_query(enum bpf_attach_type attach_type)
>  	test_sockmap_progs_query__destroy(skel);
>  }
>  
> +#define MAX_EVENTS 10
> +static void test_sockmap_skb_verdict_shutdown(void)
> +{
> +	int n, err, map, verdict, s, c0, c1, p0, p1;
> +	struct epoll_event ev, events[MAX_EVENTS];
> +	struct test_sockmap_pass_prog *skel;
> +	int epollfd;
> +	int zero = 0;
> +	char b;
> +
> +	skel = test_sockmap_pass_prog__open_and_load();
> +	if (!ASSERT_OK_PTR(skel, "open_and_load"))
> +		return;
> +
> +	verdict = bpf_program__fd(skel->progs.prog_skb_verdict);
> +	map = bpf_map__fd(skel->maps.sock_map_rx);
> +
> +	err = bpf_prog_attach(verdict, map, BPF_SK_SKB_STREAM_VERDICT, 0);
> +	if (!ASSERT_OK(err, "bpf_prog_attach"))
> +		goto out;
> +
> +	s = socket_loopback(AF_INET, SOCK_STREAM);
> +	if (s < 0)
> +		goto out;
> +	err = create_socket_pairs(s, AF_INET, SOCK_STREAM, &c0, &c1, &p0, &p1);
> +	if (err < 0)
> +		goto out;
> +
> +	err = bpf_map_update_elem(map, &zero, &c1, BPF_NOEXIST);
> +	if (err < 0)
> +		goto out_close;
> +
> +	shutdown(c0, SHUT_RDWR);
> +	shutdown(p1, SHUT_WR);
> +
> +	ev.events = EPOLLIN;
> +	ev.data.fd = c1;
> +
> +	epollfd = epoll_create1(0);
> +	if (!ASSERT_GT(epollfd, -1, "epoll_create(0)"))
> +		goto out_close;
> +	err = epoll_ctl(epollfd, EPOLL_CTL_ADD, c1, &ev);
> +	if (!ASSERT_OK(err, "epoll_ctl(EPOLL_CTL_ADD)"))
> +		goto out_close;
> +	err = epoll_wait(epollfd, events, MAX_EVENTS, -1);
> +	if (!ASSERT_EQ(err, 1, "epoll_wait(fd)"))
> +		goto out_close;
> +
> +	n = recv(c1, &b, 1, SOCK_NONBLOCK);
> +	ASSERT_EQ(n, 0, "recv_timeout(fin)");
> +	n = recv(p0, &b, 1, SOCK_NONBLOCK);
> +	ASSERT_EQ(n, 0, "recv_timeout(fin)");
> +
> +out_close:
> +	close(c0);
> +	close(p0);
> +	close(c1);
> +	close(p1);
> +out:
> +	test_sockmap_pass_prog__destroy(skel);
> +}
> +

This test has me scratching my head. I don't grasp what we're testing
with (c0, p0) socket pair, since c0 is not in any sockmap?