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 
23 static int foo;
24 static int baz;
25 static int bar;
26 
27 /*
28  * The "foo" file where a static variable is read from and written to.
29  */
30 static ssize_t foo_show(struct kobject *kobj, struct kobj_attribute *attr,
31 			char *buf)
32 {
33 	return sprintf(buf, "%d\n", foo);
34 }
35 
36 static 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. */
49 static 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  */
56 static 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 
68 static 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 
84 static struct kobj_attribute baz_attribute =
85 	__ATTR(baz, 0664, b_show, b_store);
86 static 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  */
94 static 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  */
107 static struct attribute_group attr_group = {
108 	.attrs = attrs,
109 };
110 
111 static struct kobject *example_kobj;
112 
113 static 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 
138 static void __exit example_exit(void)
139 {
140 	kobject_put(example_kobj);
141 }
142 
143 module_init(example_init);
144 module_exit(example_exit);
145 MODULE_LICENSE("GPL v2");
146 MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>");
147