Re: [PATCH 6/6] doc: Extend zero-recv test with methods using msghdr

[Stefano Brivio <sbrivio@redhat.com>]

On Wed, 17 Jul 2024 14:52:23 +1000
David Gibson <david@gibson.dropbear.id.au> wrote:

> This test program verifies that we can receive and discard datagrams by
> using recv() with a NULL buffer and zero-length.  Extend it to verify it
> also works using recvmsg() and either an iov with a zero-length NULL
> buffer or an iov that itself is NULL and zero-length.
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>  doc/platform-requirements/recv-zero.c | 60 +++++++++++++++++++++++----
>  1 file changed, 52 insertions(+), 8 deletions(-)
> 
> diff --git a/doc/platform-requirements/recv-zero.c b/doc/platform-requirements/recv-zero.c
> index f161e5c2..ab27704d 100644
> --- a/doc/platform-requirements/recv-zero.c
> +++ b/doc/platform-requirements/recv-zero.c
> @@ -23,11 +23,27 @@
>  
>  #define DSTPORT	13257U
>  
> +enum discard_method {
> +	DISCARD_NULL_BUF,
> +	DISCARD_ZERO_IOV,
> +	DISCARD_NULL_IOV,
> +	NUM_METHODS,
> +};
> +
>  /* 127.0.0.1:DSTPORT */
>  static const struct sockaddr_in lo_dst = SOCKADDR_INIT(INADDR_LOOPBACK, DSTPORT);
>  
> -static void test_discard(void)
> +static void test_discard(enum discard_method method)
>  {
> +	struct iovec zero_iov = { .iov_base = NULL, .iov_len = 0, };
> +	struct msghdr mh_zero = {
> +		.msg_iov = &zero_iov,
> +		.msg_iovlen = 1,
> +	};
> +	struct msghdr mh_null = {
> +		.msg_iov = NULL,
> +		.msg_iovlen = 0,
> +	};
>  	long token1, token2;
>  	int recv_s, send_s;
>  	ssize_t rc;
> @@ -46,11 +62,36 @@ static void test_discard(void)
>  	send_token(send_s, token1);
>  	send_token(send_s, token2);
>  
> -	/* cppcheck-suppress nullPointer */
> -	rc = recv(recv_s, NULL, 0, MSG_DONTWAIT);
> -	if (rc < 0)
> -		die("discarding recv(): %s\n", strerror(errno));
> -	
> +	switch (method) {
> +	case DISCARD_NULL_BUF:
> +		/* cppcheck-suppress nullPointer */
> +		rc = recv(recv_s, NULL, 0, MSG_DONTWAIT);
> +		if (rc < 0)
> +			die("discarding recv(): %s\n", strerror(errno));
> +		break;
> +
> +	case DISCARD_ZERO_IOV:
> +		rc = recvmsg(recv_s, &mh_zero, MSG_DONTWAIT);
> +		if (rc < 0)
> +			die("recvmsg() with zero-length buffer: %s\n",
> +			    strerror(errno));
> +		if (!((unsigned)mh_zero.msg_flags & MSG_TRUNC))
> +			die("Missing MSG_TRUNC flag\n");
> +		break;
> +
> +	case DISCARD_NULL_IOV:
> +		rc = recvmsg(recv_s, &mh_null, MSG_DONTWAIT);
> +		if (rc < 0)
> +			die("recvmsg() with zero-length iov: %s\n",
> +			    strerror(errno));
> +		if (!((unsigned)mh_null.msg_flags & MSG_TRUNC))
> +			die("Missing MSG_TRUNC flag\n");
> +		break;
> +
> +	default:
> +		die("Bad method\n");
> +	}
> +
>  	recv_token(recv_s, token2);
>  
>  	/* cppcheck-suppress nullPointer */
> @@ -63,12 +104,15 @@ static void test_discard(void)
>  
>  int main(int argc, char *argv[])
>  {
> +	enum discard_method method;
> +
>  	(void)argc;
>  	(void)argv;
>  
> -	test_discard();
> +	for (method = 0; method < NUM_METHODS; method++)
> +		test_discard(method);
>  
> -	printf("Discarding datagrams with a 0-length recv() seems to work\n");
> +	printf("Discarding datagrams with a 0-length receives seems to work\n");

Nit: also fixed up on merge: "with 0-length receives".

>  
>  	exit(0);
>  }

-- 
Stefano