1/*
2 * Sample kobject implementation
3 *
4 * Copyright (C) 2004-2007 Greg Kroah-Hartman <greg@kroah.com>
5 * Copyright (C) 2007 Novell Inc.
6 *
7 * Released under the GPL version 2 only.
8 *
9 */
10#include <linux/kobject.h>
11#include <linux/string.h>
12#include <linux/sysfs.h>
13#include <linux/module.h>
14#include <linux/init.h>
15
16/*
17 * This module shows how to create a simple subdirectory in sysfs called
18 * /sys/kernel/kobject-example  In that directory, 3 files are created:
19 * "foo", "baz", and "bar".  If an integer is written to these files, it can be
20 * later read out of it.
21 */
22
23static int foo;
24static int baz;
25static int bar;
26
27/*
28 * The "foo" file where a static variable is read from and written to.
29 */
30static ssize_t foo_show(struct kobject *kobj, struct kobj_attribute *attr,
31			char *buf)
32{
33	return sprintf(buf, "%d\n", foo);
34}
35
36static ssize_t foo_store(struct kobject *kobj, struct kobj_attribute *attr,
37			 const char *buf, size_t count)
38{
39	int ret;
40
41	ret = kstrtoint(buf, 10, &foo);
42	if (ret < 0)
43		return ret;
44
45	return count;
46}
47
48/* Sysfs attributes cannot be world-writable. */
49static struct kobj_attribute foo_attribute =
50	__ATTR(foo, 0664, foo_show, foo_store);
51
52/*
53 * More complex function where we determine which variable is being accessed by
54 * looking at the attribute for the "baz" and "bar" files.
55 */
56static ssize_t b_show(struct kobject *kobj, struct kobj_attribute *attr,
57		      char *buf)
58{
59	int var;
60
61	if (strcmp(attr->attr.name, "baz") == 0)
62		var = baz;
63	else
64		var = bar;
65	return sprintf(buf, "%d\n", var);
66}
67
68static ssize_t b_store(struct kobject *kobj, struct kobj_attribute *attr,
69		       const char *buf, size_t count)
70{
71	int var, ret;
72
73	ret = kstrtoint(buf, 10, &var);
74	if (ret < 0)
75		return ret;
76
77	if (strcmp(attr->attr.name, "baz") == 0)
78		baz = var;
79	else
80		bar = var;
81	return count;
82}
83
84static struct kobj_attribute baz_attribute =
85	__ATTR(baz, 0664, b_show, b_store);
86static struct kobj_attribute bar_attribute =
87	__ATTR(bar, 0664, b_show, b_store);
88
89
90/*
91 * Create a group of attributes so that we can create and destroy them all
92 * at once.
93 */
94static struct attribute *attrs[] = {
95	&foo_attribute.attr,
96	&baz_attribute.attr,
97	&bar_attribute.attr,
98	NULL,	/* need to NULL terminate the list of attributes */
99};
100
101/*
102 * An unnamed attribute group will put all of the attributes directly in
103 * the kobject directory.  If we specify a name, a subdirectory will be
104 * created for the attributes with the directory being the name of the
105 * attribute group.
106 */
107static struct attribute_group attr_group = {
108	.attrs = attrs,
109};
110
111static struct kobject *example_kobj;
112
113static int __init example_init(void)
114{
115	int retval;
116
117	/*
118	 * Create a simple kobject with the name of "kobject_example",
119	 * located under /sys/kernel/
120	 *
121	 * As this is a simple directory, no uevent will be sent to
122	 * userspace.  That is why this function should not be used for
123	 * any type of dynamic kobjects, where the name and number are
124	 * not known ahead of time.
125	 */
126	example_kobj = kobject_create_and_add("kobject_example", kernel_kobj);
127	if (!example_kobj)
128		return -ENOMEM;
129
130	/* Create the files associated with this kobject */
131	retval = sysfs_create_group(example_kobj, &attr_group);
132	if (retval)
133		kobject_put(example_kobj);
134
135	return retval;
136}
137
138static void __exit example_exit(void)
139{
140	kobject_put(example_kobj);
141}
142
143module_init(example_init);
144module_exit(example_exit);
145MODULE_LICENSE("GPL v2");
146MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>");
147