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 /* Sysfs attributes cannot be world-writable. */
44 static struct kobj_attribute foo_attribute =
45 	__ATTR(foo, 0664, foo_show, foo_store);
46 
47 /*
48  * More complex function where we determine which variable is being accessed by
49  * looking at the attribute for the "baz" and "bar" files.
50  */
51 static ssize_t b_show(struct kobject *kobj, struct kobj_attribute *attr,
52 		      char *buf)
53 {
54 	int var;
55 
56 	if (strcmp(attr->attr.name, "baz") == 0)
57 		var = baz;
58 	else
59 		var = bar;
60 	return sprintf(buf, "%d\n", var);
61 }
62 
63 static ssize_t b_store(struct kobject *kobj, struct kobj_attribute *attr,
64 		       const char *buf, size_t count)
65 {
66 	int var;
67 
68 	sscanf(buf, "%du", &var);
69 	if (strcmp(attr->attr.name, "baz") == 0)
70 		baz = var;
71 	else
72 		bar = var;
73 	return count;
74 }
75 
76 static struct kobj_attribute baz_attribute =
77 	__ATTR(baz, 0664, b_show, b_store);
78 static struct kobj_attribute bar_attribute =
79 	__ATTR(bar, 0664, b_show, b_store);
80 
81 
82 /*
83  * Create a group of attributes so that we can create and destroy them all
84  * at once.
85  */
86 static struct attribute *attrs[] = {
87 	&foo_attribute.attr,
88 	&baz_attribute.attr,
89 	&bar_attribute.attr,
90 	NULL,	/* need to NULL terminate the list of attributes */
91 };
92 
93 /*
94  * An unnamed attribute group will put all of the attributes directly in
95  * the kobject directory.  If we specify a name, a subdirectory will be
96  * created for the attributes with the directory being the name of the
97  * attribute group.
98  */
99 static struct attribute_group attr_group = {
100 	.attrs = attrs,
101 };
102 
103 static struct kobject *example_kobj;
104 
105 static int __init example_init(void)
106 {
107 	int retval;
108 
109 	/*
110 	 * Create a simple kobject with the name of "kobject_example",
111 	 * located under /sys/kernel/
112 	 *
113 	 * As this is a simple directory, no uevent will be sent to
114 	 * userspace.  That is why this function should not be used for
115 	 * any type of dynamic kobjects, where the name and number are
116 	 * not known ahead of time.
117 	 */
118 	example_kobj = kobject_create_and_add("kobject_example", kernel_kobj);
119 	if (!example_kobj)
120 		return -ENOMEM;
121 
122 	/* Create the files associated with this kobject */
123 	retval = sysfs_create_group(example_kobj, &attr_group);
124 	if (retval)
125 		kobject_put(example_kobj);
126 
127 	return retval;
128 }
129 
130 static void __exit example_exit(void)
131 {
132 	kobject_put(example_kobj);
133 }
134 
135 module_init(example_init);
136 module_exit(example_exit);
137 MODULE_LICENSE("GPL");
138 MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>");
139