Root/samples/kobject/kset-example.c

1/*
2 * Sample kset and ktype 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/slab.h>
14#include <linux/module.h>
15#include <linux/init.h>
16
17/*
18 * This module shows how to create a kset in sysfs called
19 * /sys/kernel/kset-example
20 * Then tree kobjects are created and assigned to this kset, "foo", "baz",
21 * and "bar". In those kobjects, attributes of the same name are also
22 * created and if an integer is written to these files, it can be later
23 * read out of it.
24 */
25
26
27/*
28 * This is our "object" that we will create a few of and register them with
29 * sysfs.
30 */
31struct foo_obj {
32    struct kobject kobj;
33    int foo;
34    int baz;
35    int bar;
36};
37#define to_foo_obj(x) container_of(x, struct foo_obj, kobj)
38
39/* a custom attribute that works just for a struct foo_obj. */
40struct foo_attribute {
41    struct attribute attr;
42    ssize_t (*show)(struct foo_obj *foo, struct foo_attribute *attr, char *buf);
43    ssize_t (*store)(struct foo_obj *foo, struct foo_attribute *attr, const char *buf, size_t count);
44};
45#define to_foo_attr(x) container_of(x, struct foo_attribute, attr)
46
47/*
48 * The default show function that must be passed to sysfs. This will be
49 * called by sysfs for whenever a show function is called by the user on a
50 * sysfs file associated with the kobjects we have registered. We need to
51 * transpose back from a "default" kobject to our custom struct foo_obj and
52 * then call the show function for that specific object.
53 */
54static ssize_t foo_attr_show(struct kobject *kobj,
55                 struct attribute *attr,
56                 char *buf)
57{
58    struct foo_attribute *attribute;
59    struct foo_obj *foo;
60
61    attribute = to_foo_attr(attr);
62    foo = to_foo_obj(kobj);
63
64    if (!attribute->show)
65        return -EIO;
66
67    return attribute->show(foo, attribute, buf);
68}
69
70/*
71 * Just like the default show function above, but this one is for when the
72 * sysfs "store" is requested (when a value is written to a file.)
73 */
74static ssize_t foo_attr_store(struct kobject *kobj,
75                  struct attribute *attr,
76                  const char *buf, size_t len)
77{
78    struct foo_attribute *attribute;
79    struct foo_obj *foo;
80
81    attribute = to_foo_attr(attr);
82    foo = to_foo_obj(kobj);
83
84    if (!attribute->store)
85        return -EIO;
86
87    return attribute->store(foo, attribute, buf, len);
88}
89
90/* Our custom sysfs_ops that we will associate with our ktype later on */
91static const struct sysfs_ops foo_sysfs_ops = {
92    .show = foo_attr_show,
93    .store = foo_attr_store,
94};
95
96/*
97 * The release function for our object. This is REQUIRED by the kernel to
98 * have. We free the memory held in our object here.
99 *
100 * NEVER try to get away with just a "blank" release function to try to be
101 * smarter than the kernel. Turns out, no one ever is...
102 */
103static void foo_release(struct kobject *kobj)
104{
105    struct foo_obj *foo;
106
107    foo = to_foo_obj(kobj);
108    kfree(foo);
109}
110
111/*
112 * The "foo" file where the .foo variable is read from and written to.
113 */
114static ssize_t foo_show(struct foo_obj *foo_obj, struct foo_attribute *attr,
115            char *buf)
116{
117    return sprintf(buf, "%d\n", foo_obj->foo);
118}
119
120static ssize_t foo_store(struct foo_obj *foo_obj, struct foo_attribute *attr,
121             const char *buf, size_t count)
122{
123    sscanf(buf, "%du", &foo_obj->foo);
124    return count;
125}
126
127static struct foo_attribute foo_attribute =
128    __ATTR(foo, 0666, foo_show, foo_store);
129
130/*
131 * More complex function where we determine which variable is being accessed by
132 * looking at the attribute for the "baz" and "bar" files.
133 */
134static ssize_t b_show(struct foo_obj *foo_obj, struct foo_attribute *attr,
135              char *buf)
136{
137    int var;
138
139    if (strcmp(attr->attr.name, "baz") == 0)
140        var = foo_obj->baz;
141    else
142        var = foo_obj->bar;
143    return sprintf(buf, "%d\n", var);
144}
145
146static ssize_t b_store(struct foo_obj *foo_obj, struct foo_attribute *attr,
147               const char *buf, size_t count)
148{
149    int var;
150
151    sscanf(buf, "%du", &var);
152    if (strcmp(attr->attr.name, "baz") == 0)
153        foo_obj->baz = var;
154    else
155        foo_obj->bar = var;
156    return count;
157}
158
159static struct foo_attribute baz_attribute =
160    __ATTR(baz, 0666, b_show, b_store);
161static struct foo_attribute bar_attribute =
162    __ATTR(bar, 0666, b_show, b_store);
163
164/*
165 * Create a group of attributes so that we can create and destroy them all
166 * at once.
167 */
168static struct attribute *foo_default_attrs[] = {
169    &foo_attribute.attr,
170    &baz_attribute.attr,
171    &bar_attribute.attr,
172    NULL, /* need to NULL terminate the list of attributes */
173};
174
175/*
176 * Our own ktype for our kobjects. Here we specify our sysfs ops, the
177 * release function, and the set of default attributes we want created
178 * whenever a kobject of this type is registered with the kernel.
179 */
180static struct kobj_type foo_ktype = {
181    .sysfs_ops = &foo_sysfs_ops,
182    .release = foo_release,
183    .default_attrs = foo_default_attrs,
184};
185
186static struct kset *example_kset;
187static struct foo_obj *foo_obj;
188static struct foo_obj *bar_obj;
189static struct foo_obj *baz_obj;
190
191static struct foo_obj *create_foo_obj(const char *name)
192{
193    struct foo_obj *foo;
194    int retval;
195
196    /* allocate the memory for the whole object */
197    foo = kzalloc(sizeof(*foo), GFP_KERNEL);
198    if (!foo)
199        return NULL;
200
201    /*
202     * As we have a kset for this kobject, we need to set it before calling
203     * the kobject core.
204     */
205    foo->kobj.kset = example_kset;
206
207    /*
208     * Initialize and add the kobject to the kernel. All the default files
209     * will be created here. As we have already specified a kset for this
210     * kobject, we don't have to set a parent for the kobject, the kobject
211     * will be placed beneath that kset automatically.
212     */
213    retval = kobject_init_and_add(&foo->kobj, &foo_ktype, NULL, "%s", name);
214    if (retval) {
215        kobject_put(&foo->kobj);
216        return NULL;
217    }
218
219    /*
220     * We are always responsible for sending the uevent that the kobject
221     * was added to the system.
222     */
223    kobject_uevent(&foo->kobj, KOBJ_ADD);
224
225    return foo;
226}
227
228static void destroy_foo_obj(struct foo_obj *foo)
229{
230    kobject_put(&foo->kobj);
231}
232
233static int __init example_init(void)
234{
235    /*
236     * Create a kset with the name of "kset_example",
237     * located under /sys/kernel/
238     */
239    example_kset = kset_create_and_add("kset_example", NULL, kernel_kobj);
240    if (!example_kset)
241        return -ENOMEM;
242
243    /*
244     * Create three objects and register them with our kset
245     */
246    foo_obj = create_foo_obj("foo");
247    if (!foo_obj)
248        goto foo_error;
249
250    bar_obj = create_foo_obj("bar");
251    if (!bar_obj)
252        goto bar_error;
253
254    baz_obj = create_foo_obj("baz");
255    if (!baz_obj)
256        goto baz_error;
257
258    return 0;
259
260baz_error:
261    destroy_foo_obj(bar_obj);
262bar_error:
263    destroy_foo_obj(foo_obj);
264foo_error:
265    return -EINVAL;
266}
267
268static void __exit example_exit(void)
269{
270    destroy_foo_obj(baz_obj);
271    destroy_foo_obj(bar_obj);
272    destroy_foo_obj(foo_obj);
273    kset_unregister(example_kset);
274}
275
276module_init(example_init);
277module_exit(example_exit);
278MODULE_LICENSE("GPL");
279MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>");
280

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