Linux 7.0: explicitly set setlease handler to kernel implementation

The upcoming 7.0 kernel will no longer fall back to generic_setlease(),
instead returning EINVAL if .setlease is NULL. So, we set it explicitly.

To ensure that we catch any future kernel change, adds a sanity test for
F_SETLEASE and F_GETLEASE too. Since this is a Linux-specific test,
also a small adjustment to the test runner to allow OS-specific helper
programs.

Sponsored-by: TrueNAS
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rob Norris <rob.norris@truenas.com>
Closes #18215

tests/zfs-tests/cmd/.gitignore

@@ -58,3 +58,4 @@
 /sha2_test
 /idmap_util
 /statx
+/setlease

tests/zfs-tests/cmd/Makefile.am

@@ -130,6 +130,7 @@ scripts_zfs_tests_bin_PROGRAMS += %D%/statx
 scripts_zfs_tests_bin_PROGRAMS += %D%/xattrtest
 scripts_zfs_tests_bin_PROGRAMS += %D%/zed_fd_spill-zedlet
 scripts_zfs_tests_bin_PROGRAMS += %D%/idmap_util
+scripts_zfs_tests_bin_PROGRAMS += %D%/setlease
 
 %C%_idmap_util_LDADD = libspl.la
 

tests/zfs-tests/cmd/setlease.c

@@ -0,0 +1,126 @@
+// SPDX-License-Identifier: CDDL-1.0
+/*
+ * CDDL HEADER START
+ *
+ * The contents of this file are subject to the terms of the
+ * Common Development and Distribution License (the "License").
+ * You may not use this file except in compliance with the License.
+ *
+ * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+ * or https://opensource.org/licenses/CDDL-1.0.
+ * See the License for the specific language governing permissions
+ * and limitations under the License.
+ *
+ * When distributing Covered Code, include this CDDL HEADER in each
+ * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+ * If applicable, add the following below this CDDL HEADER, with the
+ * fields enclosed by brackets "[]" replaced with your own identifying
+ * information: Portions Copyright [yyyy] [name of copyright owner]
+ *
+ * CDDL HEADER END
+ */
+
+/*
+ * Copyright (c) 2026, TrueNAS.
+ */
+
+/*
+ * This is a sanity check test for the F_SETLEASE and F_GETLEASE fcntl() calls.
+ * We use the generic kernel implementation, but we want to be alerted if it
+ * ever breaks.
+ *
+ * This is not a comprehensive test. It would be nice if it could be!
+ */
+
+#ifndef _GNU_SOURCE
+#define	_GNU_SOURCE
+#endif
+
+#include <stdio.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <string.h>
+
+static int
+get_lease(int fd) {
+	int r = fcntl(fd, F_GETLEASE);
+	if (r < 0) {
+		perror("fcntl(GETLEASE)");
+		exit(2);
+	}
+	return (r);
+}
+
+static int
+set_lease(int fd, int lease) {
+	return (fcntl(fd, F_SETLEASE, lease) < 0 ? errno : 0);
+}
+
+static const char *lease_str[] = {
+	[F_RDLCK] = "RDLCK",
+	[F_WRLCK] = "WRLCK",
+	[F_UNLCK] = "UNLCK",
+};
+
+static void
+assert_lease(int fd, int expect) {
+	int got = get_lease(fd);
+	if (got != expect) {
+		fprintf(stderr, "ASSERT_LEASE: expected %s [%d], got %s [%d]\n",
+		    lease_str[expect], expect, lease_str[got], got);
+		abort();
+	}
+	printf("ok: lease is %s\n", lease_str[got]);
+}
+
+static void
+assert_set_lease(int fd, int lease) {
+	int err = set_lease(fd, lease);
+	if (err != 0) {
+		fprintf(stderr, "ASSERT_SET_LEASE: tried %s [%d], error: %s\n",
+		    lease_str[lease], lease, strerror(err));
+		abort();
+	}
+	printf("ok: set lease to %s\n", lease_str[lease]);
+}
+
+int
+main(int argc, char **argv)
+{
+	if (argc != 2) {
+		fprintf(stderr, "usage: %s <filename>\n", argv[0]);
+		exit(1);
+	}
+
+	/* create and open file, read+write */
+	int fd = open(argv[1], O_CREAT|O_RDONLY, S_IRWXU|S_IRWXG|S_IRWXO);
+	if (fd < 0) {
+		perror("open");
+		exit(2);
+	}
+	printf("ok: opened file RDONLY\n");
+
+	/* fd starts with no lease */
+	assert_lease(fd, F_UNLCK);
+
+	/* fd is readonly, so can take read lease */
+	assert_set_lease(fd, F_RDLCK);
+	/* confirm read lease */
+	assert_lease(fd, F_RDLCK);
+
+	/* no other openers, so can take write lease */
+	assert_set_lease(fd, F_WRLCK);
+	/* confirm write lease */
+	assert_lease(fd, F_WRLCK);
+
+	/* release lease */
+	assert_set_lease(fd, F_UNLCK);
+	/* confirm lease released */
+	assert_lease(fd, F_UNLCK);
+
+	close(fd);
+
+	return (0);
+}