A dumb test that calling close() on a pipe/socket fd dislodges another

thread in the same process waiting for I/O on the fd.

regress/sys/kern/dislodgefd/Makefile

@@ -0,0 +1,9 @@
+#	$NetBSD: Makefile,v 1.1 2023/10/13 18:46:22 ad Exp $
+
+NOMAN=		# defined
+
+PROG=		dislodgefd
+WARNS?=		4
+LDADD=		-lpthread
+
+.include <bsd.prog.mk>

regress/sys/kern/dislodgefd/dislodgefd.c

@@ -0,0 +1,80 @@
+/*	$NetBSD: dislodgefd.c,v 1.1 2023/10/13 18:46:22 ad Exp $	*/
+
+/*-
+ * Copyright (c) 2023 The NetBSD Foundation, Inc.
+ * All rights reserved.
+ *
+ * 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.
+ *
+ * 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/socket.h>
+#include <sys/un.h>
+
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <err.h>
+
+pthread_barrier_t	barrier;
+int			fds[2];
+
+static void *
+reader(void *cookie)
+{
+	char buf[1];
+
+	(void)pthread_barrier_wait(&barrier);
+	printf("reader(): commencing read, this should error out... after 1s\n");
+	if (read(fds[0], buf, sizeof(buf)) == -1)
+		err(1, "read");
+
+	printf("reader(): read terminated without error??\n");
+	return NULL;
+}
+
+int
+main(int argc, char *argv[])
+{
+	pthread_t pt;
+
+	if (argc > 1 && strcmp(argv[1], "pipe") == 0) {
+		if (pipe(fds))
+			err(1, "pipe");
+	} else {
+		if (socketpair(PF_LOCAL, SOCK_STREAM, 0, fds) < 0)
+			err(1, "socketpair");
+	}
+	pthread_barrier_init(&barrier, NULL, 2);
+	if (pthread_create(&pt, NULL, reader, NULL)) {
+		errx(1, "pthread_create failed");
+	}
+	(void)pthread_barrier_wait(&barrier);
+	sleep(1);
+	printf("main(): closing the reader side fd..\n");
+	close(fds[0]);
+	printf("main(): sleeping again for a bit..\n");
+	sleep(1);
+	printf("main(): exiting.\n");
+	return 0;
+}