projects/linux·blob v3.13 · refs

137 lines · 3.2 KiB

1/*
2 * Sample kobject implementation
3 *
4 * Copyright (C) 2004-2007 Greg Kroah-Hartman <[email protected]>
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 sscanf(buf, "%du", &foo);
40 return count;
41}
42
43static 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 */
50static 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
62static 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
75static struct kobj_attribute baz_attribute =
76 __ATTR(baz, 0666, b_show, b_store);
77static 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 */
85static 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 */
98static struct attribute_group attr_group = {
99 .attrs = attrs,
100};
101
102static struct kobject *example_kobj;
103
104static 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
129static void __exit example_exit(void)
130{
131 kobject_put(example_kobj);
132}
133
134module_init(example_init);
135module_exit(example_exit);
136MODULE_LICENSE("GPL");
137MODULE_AUTHOR("Greg Kroah-Hartman <[email protected]>");