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>");