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

On Wed, 17 Jul 2024 14:52:23 +1000
David Gibson <david(a)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(a)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