1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Sample kset and ktype implementation
4 *
5 * Copyright (C) 2004-2007 Greg Kroah-Hartman <greg@kroah.com>
6 * Copyright (C) 2007 Novell Inc.
7 */
8#include <linux/kobject.h>
9#include <linux/string.h>
10#include <linux/sysfs.h>
11#include <linux/slab.h>
12#include <linux/module.h>
13#include <linux/init.h>
14
15/*
16 * This module shows how to create a kset in sysfs called
17 * /sys/kernel/kset-example
18 * Then tree kobjects are created and assigned to this kset, "foo", "baz",
19 * and "bar".  In those kobjects, attributes of the same name are also
20 * created and if an integer is written to these files, it can be later
21 * read out of it.
22 */
23
24
25/*
26 * This is our "object" that we will create a few of and register them with
27 * sysfs.
28 */
29struct foo_obj {
30	struct kobject kobj;
31	int foo;
32	int baz;
33	int bar;
34};
35#define to_foo_obj(x) container_of(x, struct foo_obj, kobj)
36
37/* a custom attribute that works just for a struct foo_obj. */
38struct foo_attribute {
39	struct attribute attr;
40	ssize_t (*show)(struct foo_obj *foo, struct foo_attribute *attr, char *buf);
41	ssize_t (*store)(struct foo_obj *foo, struct foo_attribute *attr, const char *buf, size_t count);
42};
43#define to_foo_attr(x) container_of(x, struct foo_attribute, attr)
44
45/*
46 * The default show function that must be passed to sysfs.  This will be
47 * called by sysfs for whenever a show function is called by the user on a
48 * sysfs file associated with the kobjects we have registered.  We need to
49 * transpose back from a "default" kobject to our custom struct foo_obj and
50 * then call the show function for that specific object.
51 */
52static ssize_t foo_attr_show(struct kobject *kobj,
53			     struct attribute *attr,
54			     char *buf)
55{
56	struct foo_attribute *attribute;
57	struct foo_obj *foo;
58
59	attribute = to_foo_attr(attr);
60	foo = to_foo_obj(kobj);
61
62	if (!attribute->show)
63		return -EIO;
64
65	return attribute->show(foo, attribute, buf);
66}
67
68/*
69 * Just like the default show function above, but this one is for when the
70 * sysfs "store" is requested (when a value is written to a file.)
71 */
72static ssize_t foo_attr_store(struct kobject *kobj,
73			      struct attribute *attr,
74			      const char *buf, size_t len)
75{
76	struct foo_attribute *attribute;
77	struct foo_obj *foo;
78
79	attribute = to_foo_attr(attr);
80	foo = to_foo_obj(kobj);
81
82	if (!attribute->store)
83		return -EIO;
84
85	return attribute->store(foo, attribute, buf, len);
86}
87
88/* Our custom sysfs_ops that we will associate with our ktype later on */
89static const struct sysfs_ops foo_sysfs_ops = {
90	.show = foo_attr_show,
91	.store = foo_attr_store,
92};
93
94/*
95 * The release function for our object.  This is REQUIRED by the kernel to
96 * have.  We free the memory held in our object here.
97 *
98 * NEVER try to get away with just a "blank" release function to try to be
99 * smarter than the kernel.  Turns out, no one ever is...
100 */
101static void foo_release(struct kobject *kobj)
102{
103	struct foo_obj *foo;
104
105	foo = to_foo_obj(kobj);
106	kfree(foo);
107}
108
109/*
110 * The "foo" file where the .foo variable is read from and written to.
111 */
112static ssize_t foo_show(struct foo_obj *foo_obj, struct foo_attribute *attr,
113			char *buf)
114{
115	return sysfs_emit(buf, "%d\n", foo_obj->foo);
116}
117
118static ssize_t foo_store(struct foo_obj *foo_obj, struct foo_attribute *attr,
119			 const char *buf, size_t count)
120{
121	int ret;
122
123	ret = kstrtoint(buf, 10, &foo_obj->foo);
124	if (ret < 0)
125		return ret;
126
127	return count;
128}
129
130/* Sysfs attributes cannot be world-writable. */
131static struct foo_attribute foo_attribute =
132	__ATTR(foo, 0664, foo_show, foo_store);
133
134/*
135 * More complex function where we determine which variable is being accessed by
136 * looking at the attribute for the "baz" and "bar" files.
137 */
138static ssize_t b_show(struct foo_obj *foo_obj, struct foo_attribute *attr,
139		      char *buf)
140{
141	int var;
142
143	if (strcmp(attr->attr.name, "baz") == 0)
144		var = foo_obj->baz;
145	else
146		var = foo_obj->bar;
147	return sysfs_emit(buf, "%d\n", var);
148}
149
150static ssize_t b_store(struct foo_obj *foo_obj, struct foo_attribute *attr,
151		       const char *buf, size_t count)
152{
153	int var, ret;
154
155	ret = kstrtoint(buf, 10, &var);
156	if (ret < 0)
157		return ret;
158
159	if (strcmp(attr->attr.name, "baz") == 0)
160		foo_obj->baz = var;
161	else
162		foo_obj->bar = var;
163	return count;
164}
165
166static struct foo_attribute baz_attribute =
167	__ATTR(baz, 0664, b_show, b_store);
168static struct foo_attribute bar_attribute =
169	__ATTR(bar, 0664, b_show, b_store);
170
171/*
172 * Create a group of attributes so that we can create and destroy them all
173 * at once.
174 */
175static struct attribute *foo_default_attrs[] = {
176	&foo_attribute.attr,
177	&baz_attribute.attr,
178	&bar_attribute.attr,
179	NULL,	/* need to NULL terminate the list of attributes */
180};
181ATTRIBUTE_GROUPS(foo_default);
182
183/*
184 * Our own ktype for our kobjects.  Here we specify our sysfs ops, the
185 * release function, and the set of default attributes we want created
186 * whenever a kobject of this type is registered with the kernel.
187 */
188static const struct kobj_type foo_ktype = {
189	.sysfs_ops = &foo_sysfs_ops,
190	.release = foo_release,
191	.default_groups = foo_default_groups,
192};
193
194static struct kset *example_kset;
195static struct foo_obj *foo_obj;
196static struct foo_obj *bar_obj;
197static struct foo_obj *baz_obj;
198
199static struct foo_obj *create_foo_obj(const char *name)
200{
201	struct foo_obj *foo;
202	int retval;
203
204	/* allocate the memory for the whole object */
205	foo = kzalloc(sizeof(*foo), GFP_KERNEL);
206	if (!foo)
207		return NULL;
208
209	/*
210	 * As we have a kset for this kobject, we need to set it before calling
211	 * the kobject core.
212	 */
213	foo->kobj.kset = example_kset;
214
215	/*
216	 * Initialize and add the kobject to the kernel.  All the default files
217	 * will be created here.  As we have already specified a kset for this
218	 * kobject, we don't have to set a parent for the kobject, the kobject
219	 * will be placed beneath that kset automatically.
220	 */
221	retval = kobject_init_and_add(&foo->kobj, &foo_ktype, NULL, "%s", name);
222	if (retval) {
223		kobject_put(&foo->kobj);
224		return NULL;
225	}
226
227	/*
228	 * We are always responsible for sending the uevent that the kobject
229	 * was added to the system.
230	 */
231	kobject_uevent(&foo->kobj, KOBJ_ADD);
232
233	return foo;
234}
235
236static void destroy_foo_obj(struct foo_obj *foo)
237{
238	kobject_put(&foo->kobj);
239}
240
241static int __init example_init(void)
242{
243	/*
244	 * Create a kset with the name of "kset_example",
245	 * located under /sys/kernel/
246	 */
247	example_kset = kset_create_and_add("kset_example", NULL, kernel_kobj);
248	if (!example_kset)
249		return -ENOMEM;
250
251	/*
252	 * Create three objects and register them with our kset
253	 */
254	foo_obj = create_foo_obj("foo");
255	if (!foo_obj)
256		goto foo_error;
257
258	bar_obj = create_foo_obj("bar");
259	if (!bar_obj)
260		goto bar_error;
261
262	baz_obj = create_foo_obj("baz");
263	if (!baz_obj)
264		goto baz_error;
265
266	return 0;
267
268baz_error:
269	destroy_foo_obj(bar_obj);
270bar_error:
271	destroy_foo_obj(foo_obj);
272foo_error:
273	kset_unregister(example_kset);
274	return -EINVAL;
275}
276
277static void __exit example_exit(void)
278{
279	destroy_foo_obj(baz_obj);
280	destroy_foo_obj(bar_obj);
281	destroy_foo_obj(foo_obj);
282	kset_unregister(example_kset);
283}
284
285module_init(example_init);
286module_exit(example_exit);
287MODULE_LICENSE("GPL v2");
288MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>");
289