Subject: Re: [PATCH bpf-next v2 2/4] bpf: sockmap, add a sendmsg test so we can check that path

From: Jakub Sitnicki <[email-masked]>
Date: Fri, 26 Jan 2024 13:17:24 +0100

On Wed, Jan 24, 2024 at 10:54 AM -08, John Fastabend wrote:
> Sendmsg path with multiple buffers is slightly different from a single
> send in how we have to handle and walk the sg when doing pops. Lets
> ensure this walk is correct.
>
> Signed-off-by: John Fastabend <[email-masked]>
> ---
>  .../bpf/prog_tests/sockmap_helpers.h          |  8 +++
>  .../bpf/prog_tests/sockmap_msg_helpers.c      | 53 +++++++++++++++++++
>  2 files changed, 61 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/sockmap_helpers.h b/tools/testing/selftests/bpf/prog_tests/sockmap_helpers.h
> index 781cbdf01d7b..4d8d24482032 100644
> --- a/tools/testing/selftests/bpf/prog_tests/sockmap_helpers.h
> +++ b/tools/testing/selftests/bpf/prog_tests/sockmap_helpers.h
> @@ -103,6 +103,14 @@
>  		__ret;                                                         \
>  	})
>  
> +#define xsendmsg(fd, msg, flags)                                               \
> +	({                                                                     \
> +		ssize_t __ret = sendmsg((fd), (msg), (flags));                 \
> +		if (__ret == -1)                                               \
> +			FAIL_ERRNO("sendmsg");                                 \
> +		__ret;                                                         \
> +	})
> +
>  #define xrecv_nonblock(fd, buf, len, flags)                                    \
>  	({                                                                     \
>  		ssize_t __ret = recv_timeout((fd), (buf), (len), (flags),      \
> diff --git a/tools/testing/selftests/bpf/prog_tests/sockmap_msg_helpers.c b/tools/testing/selftests/bpf/prog_tests/sockmap_msg_helpers.c
> index 9ffe02f45808..e5e618e84950 100644
> --- a/tools/testing/selftests/bpf/prog_tests/sockmap_msg_helpers.c
> +++ b/tools/testing/selftests/bpf/prog_tests/sockmap_msg_helpers.c
> @@ -52,6 +52,50 @@ static void pop_simple_send(struct msg_test_opts *opts, int start, int len)
>  	ASSERT_OK(cmp, "pop cmp end bytes failed");
>  }
>  
> +static void pop_complex_send(struct msg_test_opts *opts, int start, int len)
> +{
> +	struct test_sockmap_msg_helpers *skel = opts->skel;
> +	char buf[] = "abcdefghijklmnopqrstuvwxyz";
> +	size_t sent, recv, total = 0;
> +	struct msghdr msg = {0};
> +	struct iovec iov[15];
> +	char *recvbuf;
> +	int i;
> +
> +	for (i = 0; i < 15; i++) {

Always nice to use ARRAY_SIZE.

> +		iov[i].iov_base = buf;
> +		iov[i].iov_len = sizeof(buf);
> +		total += sizeof(buf);
> +	}
> +
> +	recvbuf = malloc(total);
> +	if (!recvbuf)
> +		FAIL("pop complex send malloc failure\n");

390 bytes, why not have it on stack?

> +
> +	msg.msg_iov = iov;
> +	msg.msg_iovlen = 15;
> +
> +	skel->bss->pop = true;
> +
> +	if (start == -1)
> +		start = sizeof(buf) - len - 1;
> +
> +	skel->bss->pop_start = start;
> +	skel->bss->pop_len = len;
> +
> +	sent = xsendmsg(opts->client, &msg, 0);
> +	if (sent != total)
> +		FAIL("xsend failed");
> +
> +	ASSERT_OK(skel->bss->err, "pop error");
> +
> +	recv = xrecv_nonblock(opts->server, recvbuf, total, 0);
> +	if (recv != sent - skel->bss->pop_len)
> +		FAIL("Received incorrect number number of bytes after pop");
> +
> +	free(recvbuf);
> +}
> +
>  static void test_sockmap_pop(void)
>  {
>  	struct msg_test_opts opts;
> @@ -92,6 +136,15 @@ static void test_sockmap_pop(void)
>  	/* Pop from end */
>  	pop_simple_send(&opts, POP_END, 5);
>  
> +	/* Empty pop from start of sendmsg */
> +	pop_complex_send(&opts, 0, 0);
> +	/* Pop from start of sendmsg */
> +	pop_complex_send(&opts, 0, 10);
> +	/* Pop from middle of sendmsg */
> +	pop_complex_send(&opts, 100, 10);
> +	/* Pop from end of sendmsg */
> +	pop_complex_send(&opts, 394, 10);

Isn't the start offset here past the end? 15*26=390?

> +
>  close_sockets:
>  	close(client);
>  	close(server);