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 	sscanf(buf, "%du", &foo);
40 	return count;
41 }
42 
43 static struct kobj_attribute foo_attribute =
44 	__ATTR(foo, 0666, foo_show, foo_store);
45 
46 /*
47  * More complex function where we determine which variable is being accessed by
48  * looking at the attribute for the "baz" and "bar" files.
49  */
50 static ssize_t b_show(struct kobject *kobj, struct kobj_attribute *attr,
51 		      char *buf)
52 {
53 	int var;
54 
55 	if (strcmp(attr->attr.name, "baz") == 0)
56 		var = baz;
57 	else
58 		var = bar;
59 	return sprintf(buf, "%d\n", var);
60 }
61 
62 static ssize_t b_store(struct kobject *kobj, struct kobj_attribute *attr,
63 		       const char *buf, size_t count)
64 {
65 	int var;
66 
67 	sscanf(buf, "%du", &var);
68 	if (strcmp(attr->attr.name, "baz") == 0)
69 		baz = var;
70 	else
71 		bar = var;
72 	return count;
73 }
74 
75 static struct kobj_attribute baz_attribute =
76 	__ATTR(baz, 0666, b_show, b_store);
77 static struct kobj_attribute bar_attribute =
78 	__ATTR(bar, 0666, b_show, b_store);
79 
80 
81 /*
82  * Create a group of attributes so that we can create and destroy them all
83  * at once.
84  */
85 static struct attribute *attrs[] = {
86 	&foo_attribute.attr,
87 	&baz_attribute.attr,
88 	&bar_attribute.attr,
89 	NULL,	/* need to NULL terminate the list of attributes */
90 };
91 
92 /*
93  * An unnamed attribute group will put all of the attributes directly in
94  * the kobject directory.  If we specify a name, a subdirectory will be
95  * created for the attributes with the directory being the name of the
96  * attribute group.
97  */
98 static struct attribute_group attr_group = {
99 	.attrs = attrs,
100 };
101 
102 static struct kobject *example_kobj;
103 
104 static int __init example_init(void)
105 {
106 	int retval;
107 
108 	/*
109 	 * Create a simple kobject with the name of "kobject_example",
110 	 * located under /sys/kernel/
111 	 *
112 	 * As this is a simple directory, no uevent will be sent to
113 	 * userspace.  That is why this function should not be used for
114 	 * any type of dynamic kobjects, where the name and number are
115 	 * not known ahead of time.
116 	 */
117 	example_kobj = kobject_create_and_add("kobject_example", kernel_kobj);
118 	if (!example_kobj)
119 		return -ENOMEM;
120 
121 	/* Create the files associated with this kobject */
122 	retval = sysfs_create_group(example_kobj, &attr_group);
123 	if (retval)
124 		kobject_put(example_kobj);
125 
126 	return retval;
127 }
128 
129 static void __exit example_exit(void)
130 {
131 	kobject_put(example_kobj);
132 }
133 
134 module_init(example_init);
135 module_exit(example_exit);
136 MODULE_LICENSE("GPL");
137 MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>");
138