Now add the file I really meant to add.

tests/lib/libc/sys/t_sendrecv.c

@@ -0,0 +1,135 @@
+/*	$NetBSD: t_sendrecv.c,v 1.1 2018/08/21 10:41:00 christos Exp $	*/
+
+/*-
+ * Copyright (c) 2018 The NetBSD Foundation, Inc.
+ * All rights reserved.
+ *
+ * This code is derived from software contributed to The NetBSD Foundation
+ * by Christos Zoulas.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. All advertising materials mentioning features or use of this software
+ *    must display the following acknowledgement:
+ *        This product includes software developed by the NetBSD
+ *        Foundation, Inc. and its contributors.
+ * 4. Neither the name of The NetBSD Foundation nor the names of its
+ *    contributors may be used to endorse or promote products derived
+ *    from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+ * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+#include <sys/cdefs.h>
+__RCSID("$NetBSD: t_sendrecv.c,v 1.1 2018/08/21 10:41:00 christos Exp $");
+
+#include <atf-c.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+
+#include <string.h>
+#include <stdint.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sched.h>
+
+ATF_TC(sendrecv_basic);
+ATF_TC_HEAD(sendrecv_basic, tc)
+{
+	atf_tc_set_md_var(tc, "descr", "A basic test of sendrecv(2)");
+}
+
+#define COUNT 1000
+
+union packet {
+	uint8_t buf[1316];
+	uintmax_t seq;
+};
+
+static void
+sender(int fd)
+{
+	union packet p;
+	ssize_t n;
+	p.seq = 0;
+	for (size_t i = 0; i < COUNT; i++) {
+		for (; (n = send(fd, &p, sizeof(p), 0)) == sizeof(p);
+		    p.seq++)
+			continue;
+//		printf(">>%zd %d %ju\n", n, errno, p.seq);
+		ATF_REQUIRE_MSG(errno == ENOBUFS, "send %s", strerror(errno));
+	}
+}
+
+static void
+receiver(int fd)
+{
+	union packet p;
+	ssize_t n;
+	uintmax_t seq = 0;
+
+	for (size_t i = 0; i < COUNT; i++) {
+		while ((n = recv(fd, &p, sizeof(p), 0), sizeof(p))
+		    == sizeof(p))
+		{
+//			if (p.seq != seq)
+//				printf("%ju != %ju\n", p.seq, seq);
+			seq = p.seq + 1;
+		}
+		printf("<<%zd %d %ju\n", n, errno, seq);
+		if (n == 0)
+			return;
+		ATF_REQUIRE_EQ(n, -1);
+		ATF_REQUIRE_MSG(errno == ENOBUFS, "recv %s", strerror(errno));
+	}
+}
+
+ATF_TC_BODY(sendrecv_basic, tc)
+{
+	int fd[2], error;
+
+	error = socketpair(AF_UNIX, SOCK_DGRAM, 0, fd);
+//	error = pipe(fd);
+	ATF_REQUIRE_MSG(error != -1, "socketpair failed (%s)", strerror(errno));
+
+	switch (fork()) {
+	case -1:
+		ATF_REQUIRE_MSG(errno == 0,
+		    "socketpair failed (%s)", strerror(errno));
+		/*NOTREACHED*/
+	case 0:
+		sched_yield();
+		sender(fd[0]);
+		close(fd[0]);
+		exit(EXIT_SUCCESS);
+		/*NOTREACHED*/
+	default:
+		receiver(fd[1]);
+		return;
+	}
+}
+
+ATF_TP_ADD_TCS(tp)
+{
+
+	ATF_TP_ADD_TC(tp, sendrecv_basic);
+
+	return atf_no_error();
+}