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 */
29 struct 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. */
38 struct 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 */
52 static 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 */
72 static 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 */
89 static 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 */
101 static 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 */
112 static 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
118 static 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. */
131 static 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 */
138 static 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
150 static 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
166 static struct foo_attribute baz_attribute =
167 __ATTR(baz, 0664, b_show, b_store);
168 static 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 */
175 static 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 };
181 ATTRIBUTE_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 */
188 static const struct kobj_type foo_ktype = {
189 .sysfs_ops = &foo_sysfs_ops,
190 .release = foo_release,
191 .default_groups = foo_default_groups,
192 };
193
194 static struct kset *example_kset;
195 static struct foo_obj *foo_obj;
196 static struct foo_obj *bar_obj;
197 static struct foo_obj *baz_obj;
198
199 static 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
236 static void destroy_foo_obj(struct foo_obj *foo)
237 {
238 kobject_put(&foo->kobj);
239 }
240
241 static 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
268 baz_error:
269 destroy_foo_obj(bar_obj);
270 bar_error:
271 destroy_foo_obj(foo_obj);
272 foo_error:
273 kset_unregister(example_kset);
274 return -EINVAL;
275 }
276
277 static 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
285 module_init(example_init);
286 module_exit(example_exit);
287 MODULE_DESCRIPTION("Sample kset and ktype implementation");
288 MODULE_LICENSE("GPL v2");
289 MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>");
290
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.