2 * Sample kset and ktype 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/slab.h>
14 #include <linux/module.h>
15 #include <linux/init.h>
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
28 * This is our "object" that we will create a few of and register them with
37 #define to_foo_obj(x) container_of(x, struct foo_obj, kobj)
39 /* a custom attribute that works just for a struct foo_obj. */
40 struct 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);
45 #define to_foo_attr(x) container_of(x, struct foo_attribute, attr)
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.
54 static ssize_t foo_attr_show(struct kobject *kobj,
55 struct attribute *attr,
58 struct foo_attribute *attribute;
61 attribute = to_foo_attr(attr);
62 foo = to_foo_obj(kobj);
67 return attribute->show(foo, attribute, buf);
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.)
74 static ssize_t foo_attr_store(struct kobject *kobj,
75 struct attribute *attr,
76 const char *buf, size_t len)
78 struct foo_attribute *attribute;
81 attribute = to_foo_attr(attr);
82 foo = to_foo_obj(kobj);
84 if (!attribute->store)
87 return attribute->store(foo, attribute, buf, len);
90 /* Our custom sysfs_ops that we will associate with our ktype later on */
91 static const struct sysfs_ops foo_sysfs_ops = {
92 .show = foo_attr_show,
93 .store = foo_attr_store,
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.
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...
103 static void foo_release(struct kobject *kobj)
107 foo = to_foo_obj(kobj);
112 * The "foo" file where the .foo variable is read from and written to.
114 static ssize_t foo_show(struct foo_obj *foo_obj, struct foo_attribute *attr,
117 return sprintf(buf, "%d\n", foo_obj->foo);
120 static ssize_t foo_store(struct foo_obj *foo_obj, struct foo_attribute *attr,
121 const char *buf, size_t count)
123 sscanf(buf, "%du", &foo_obj->foo);
127 /* Sysfs attributes cannot be world-writable. */
128 static struct foo_attribute foo_attribute =
129 __ATTR(foo, 0664, foo_show, foo_store);
132 * More complex function where we determine which variable is being accessed by
133 * looking at the attribute for the "baz" and "bar" files.
135 static ssize_t b_show(struct foo_obj *foo_obj, struct foo_attribute *attr,
140 if (strcmp(attr->attr.name, "baz") == 0)
144 return sprintf(buf, "%d\n", var);
147 static ssize_t b_store(struct foo_obj *foo_obj, struct foo_attribute *attr,
148 const char *buf, size_t count)
152 sscanf(buf, "%du", &var);
153 if (strcmp(attr->attr.name, "baz") == 0)
160 static struct foo_attribute baz_attribute =
161 __ATTR(baz, 0664, b_show, b_store);
162 static struct foo_attribute bar_attribute =
163 __ATTR(bar, 0664, b_show, b_store);
166 * Create a group of attributes so that we can create and destroy them all
169 static struct attribute *foo_default_attrs[] = {
173 NULL, /* need to NULL terminate the list of attributes */
177 * Our own ktype for our kobjects. Here we specify our sysfs ops, the
178 * release function, and the set of default attributes we want created
179 * whenever a kobject of this type is registered with the kernel.
181 static struct kobj_type foo_ktype = {
182 .sysfs_ops = &foo_sysfs_ops,
183 .release = foo_release,
184 .default_attrs = foo_default_attrs,
187 static struct kset *example_kset;
188 static struct foo_obj *foo_obj;
189 static struct foo_obj *bar_obj;
190 static struct foo_obj *baz_obj;
192 static struct foo_obj *create_foo_obj(const char *name)
197 /* allocate the memory for the whole object */
198 foo = kzalloc(sizeof(*foo), GFP_KERNEL);
203 * As we have a kset for this kobject, we need to set it before calling
206 foo->kobj.kset = example_kset;
209 * Initialize and add the kobject to the kernel. All the default files
210 * will be created here. As we have already specified a kset for this
211 * kobject, we don't have to set a parent for the kobject, the kobject
212 * will be placed beneath that kset automatically.
214 retval = kobject_init_and_add(&foo->kobj, &foo_ktype, NULL, "%s", name);
216 kobject_put(&foo->kobj);
221 * We are always responsible for sending the uevent that the kobject
222 * was added to the system.
224 kobject_uevent(&foo->kobj, KOBJ_ADD);
229 static void destroy_foo_obj(struct foo_obj *foo)
231 kobject_put(&foo->kobj);
234 static int __init example_init(void)
237 * Create a kset with the name of "kset_example",
238 * located under /sys/kernel/
240 example_kset = kset_create_and_add("kset_example", NULL, kernel_kobj);
245 * Create three objects and register them with our kset
247 foo_obj = create_foo_obj("foo");
251 bar_obj = create_foo_obj("bar");
255 baz_obj = create_foo_obj("baz");
262 destroy_foo_obj(bar_obj);
264 destroy_foo_obj(foo_obj);
266 kset_unregister(example_kset);
270 static void __exit example_exit(void)
272 destroy_foo_obj(baz_obj);
273 destroy_foo_obj(bar_obj);
274 destroy_foo_obj(foo_obj);
275 kset_unregister(example_kset);
278 module_init(example_init);
279 module_exit(example_exit);
280 MODULE_LICENSE("GPL");
281 MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>");