2 * Sample kobject implementation
4 * Copyright (C) 2004-2007 Greg Kroah-Hartman <greg@kroah.com>
5 * Copyright (C) 2007 Novell Inc.
7 * Released under the GPL version 2 only.
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>
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.
28 * The "foo" file where a static variable is read from and written to.
30 static ssize_t foo_show(struct kobject *kobj, struct kobj_attribute *attr,
33 return sprintf(buf, "%d\n", foo);
36 static ssize_t foo_store(struct kobject *kobj, struct kobj_attribute *attr,
37 const char *buf, size_t count)
41 ret = kstrtoint(buf, 10, &foo);
48 /* Sysfs attributes cannot be world-writable. */
49 static struct kobj_attribute foo_attribute =
50 __ATTR(foo, 0664, foo_show, foo_store);
53 * More complex function where we determine which variable is being accessed by
54 * looking at the attribute for the "baz" and "bar" files.
56 static ssize_t b_show(struct kobject *kobj, struct kobj_attribute *attr,
61 if (strcmp(attr->attr.name, "baz") == 0)
65 return sprintf(buf, "%d\n", var);
68 static ssize_t b_store(struct kobject *kobj, struct kobj_attribute *attr,
69 const char *buf, size_t count)
73 ret = kstrtoint(buf, 10, &var);
77 if (strcmp(attr->attr.name, "baz") == 0)
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);
91 * Create a group of attributes so that we can create and destroy them all
94 static struct attribute *attrs[] = {
98 NULL, /* need to NULL terminate the list of attributes */
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
107 static struct attribute_group attr_group = {
111 static struct kobject *example_kobj;
113 static int __init example_init(void)
118 * Create a simple kobject with the name of "kobject_example",
119 * located under /sys/kernel/
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.
126 example_kobj = kobject_create_and_add("kobject_example", kernel_kobj);
130 /* Create the files associated with this kobject */
131 retval = sysfs_create_group(example_kobj, &attr_group);
133 kobject_put(example_kobj);
138 static void __exit example_exit(void)
140 kobject_put(example_kobj);
143 module_init(example_init);
144 module_exit(example_exit);
145 MODULE_LICENSE("GPL v2");
146 MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>");