[PATCH v2 4/9] test_sysctl: add dedicated proc sysctl test driver

["Luis R. Rodriguez" <mcgrof@kernel.org>]

Although we have had tools/testing/selftests/sysctl/ with two
test cases these use existing kernel sysctl interfaces. We want
to expand test coverage, we can't just be looking for random
safe production values to poke at, instead just dedicate a test
driver for debugging purposes and port the existing scripts to
use it. This will make it easier for further tests to be added.

Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
---
 lib/Kconfig.debug                               |  11 +++
 lib/Makefile                                    |   1 +
 lib/test_sysctl.c                               | 106 ++++++++++++++++++++++++
 tools/testing/selftests/sysctl/config           |   1 +
 tools/testing/selftests/sysctl/run_numerictests |   4 +-
 tools/testing/selftests/sysctl/run_stringtests  |   4 +-
 6 files changed, 123 insertions(+), 4 deletions(-)
 create mode 100644 lib/test_sysctl.c
 create mode 100644 tools/testing/selftests/sysctl/config

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 64c03b07ad2f..d753fac41f78 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1975,6 +1975,17 @@ config TEST_FIRMWARE
 
 	  If unsure, say N.
 
+config TEST_SYSCTL
+	tristate "sysctl test driver"
+	default n
+	depends on PROC_SYSCTL
+	help
+	  This builds the "test_sysctl" module. This driver enables to test the
+	  proc sysctl interfaces available to drivers safely without affecting
+	  production knobs which might alter system functionality.
+
+	  If unsure, say N.
+
 config TEST_UDELAY
 	tristate "udelay test driver"
 	default n
diff --git a/lib/Makefile b/lib/Makefile
index 445a39c21f46..ac832c440d41 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -45,6 +45,7 @@ obj-$(CONFIG_TEST_HEXDUMP) += test_hexdump.o
 obj-y += kstrtox.o
 obj-$(CONFIG_TEST_BPF) += test_bpf.o
 obj-$(CONFIG_TEST_FIRMWARE) += test_firmware.o
+obj-$(CONFIG_TEST_SYSCTL) += test_sysctl.o
 obj-$(CONFIG_TEST_HASH) += test_hash.o test_siphash.o
 obj-$(CONFIG_TEST_KASAN) += test_kasan.o
 obj-$(CONFIG_TEST_KSTRTOX) += test-kstrtox.o
diff --git a/lib/test_sysctl.c b/lib/test_sysctl.c
new file mode 100644
index 000000000000..9b9ae1a95ab3
--- /dev/null
+++ b/lib/test_sysctl.c
@@ -0,0 +1,106 @@
+/*
+ * proc sysctl test driver
+ *
+ * Copyright (C) 2017 Luis R. Rodriguez <mcgrof@kernel.org>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of copyleft-next (version 0.3.1 or later) as published
+ * at http://copyleft-next.org/.
+ */
+
+/*
+ * This module provides an interface to the the proc sysctl interfaces.  This
+ * driver requires CONFIG_PROC_SYSCTL. It will not normally be loaded by the
+ * system unless explicitly requested by name. You can also build this driver
+ * into your kernel.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/init.h>
+#include <linux/list.h>
+#include <linux/module.h>
+#include <linux/printk.h>
+#include <linux/fs.h>
+#include <linux/miscdevice.h>
+#include <linux/slab.h>
+#include <linux/uaccess.h>
+#include <linux/async.h>
+#include <linux/delay.h>
+#include <linux/vmalloc.h>
+
+static int i_zero;
+static int i_one_hundred = 100;
+
+struct test_sysctl_data {
+	int int_0001;
+	char string_0001[65];
+};
+
+static struct test_sysctl_data test_data = {
+	.int_0001 = 60,
+	.string_0001 = "(none)",
+};
+
+/* These are all under /proc/sys/debug/test_sysctl/ */
+static struct ctl_table test_table[] = {
+	{
+		.procname	= "int_0001",
+		.data		= &test_data.int_0001,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= &i_zero,
+		.extra2         = &i_one_hundred,
+	},
+	{
+		.procname	= "string_0001",
+		.data		= &test_data.string_0001,
+		.maxlen		= sizeof(test_data.string_0001),
+		.mode		= 0644,
+		.proc_handler	= proc_dostring,
+	},
+	{ }
+};
+
+static struct ctl_table test_sysctl_table[] = {
+	{
+		.procname	= "test_sysctl",
+		.maxlen		= 0,
+		.mode		= 0555,
+		.child		= test_table,
+	},
+	{ }
+};
+
+static struct ctl_table test_sysctl_root_table[] = {
+	{
+		.procname	= "debug",
+		.maxlen		= 0,
+		.mode		= 0555,
+		.child		= test_sysctl_table,
+	},
+	{ }
+};
+
+static struct ctl_table_header *test_sysctl_header;
+
+static int __init test_sysctl_init(void)
+{
+	test_sysctl_header = register_sysctl_table(test_sysctl_root_table);
+	if (!test_sysctl_header)
+		return -ENOMEM;
+	return 0;
+}
+late_initcall(test_sysctl_init);
+
+static void __exit test_sysctl_exit(void)
+{
+	if (test_sysctl_header)
+		unregister_sysctl_table(test_sysctl_header);
+}
+
+module_exit(test_sysctl_exit);
+
+MODULE_AUTHOR("Luis R. Rodriguez <mcgrof@kernel.org>");
+MODULE_LICENSE("GPL");
diff --git a/tools/testing/selftests/sysctl/config b/tools/testing/selftests/sysctl/config
new file mode 100644
index 000000000000..6ca14800d755
--- /dev/null
+++ b/tools/testing/selftests/sysctl/config
@@ -0,0 +1 @@
+CONFIG_TEST_SYSCTL=y
diff --git a/tools/testing/selftests/sysctl/run_numerictests b/tools/testing/selftests/sysctl/run_numerictests
index 8510f93f2d14..cdfeef96568c 100755
--- a/tools/testing/selftests/sysctl/run_numerictests
+++ b/tools/testing/selftests/sysctl/run_numerictests
@@ -1,7 +1,7 @@
 #!/bin/sh
 
-SYSCTL="/proc/sys"
-TARGET="${SYSCTL}/vm/swappiness"
+SYSCTL="/proc/sys/debug/test_sysctl/"
+TARGET="${SYSCTL}/int_0001"
 ORIG=$(cat "${TARGET}")
 TEST_STR=$(( $ORIG + 1 ))
 
diff --git a/tools/testing/selftests/sysctl/run_stringtests b/tools/testing/selftests/sysctl/run_stringtests
index 90a9293d520c..15a646b2c527 100755
--- a/tools/testing/selftests/sysctl/run_stringtests
+++ b/tools/testing/selftests/sysctl/run_stringtests
@@ -1,7 +1,7 @@
 #!/bin/sh
 
-SYSCTL="/proc/sys"
-TARGET="${SYSCTL}/kernel/domainname"
+SYSCTL="/proc/sys/debug/test_sysctl/"
+TARGET="${SYSCTL}/string_0001"
 ORIG=$(cat "${TARGET}")
 TEST_STR="Testing sysctl"
 
-- 
2.11.0