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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Sample kset and ktype implementation
4 *
5 * Copyright (C) 2004-2007 Greg Kroah-Hartman <[email protected]>
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 three 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, const struct foo_attribute *attr, char *buf);
41 ssize_t (*store)(struct foo_obj *foo, const struct foo_attribute *attr,
42 const char *buf, size_t count);
43};
44#define to_foo_attr(x) container_of_const(x, struct foo_attribute, attr)
45
46/*
47 * The default show function that must be passed to sysfs. This will be
48 * called by sysfs for whenever a show function is called by the user on a
49 * sysfs file associated with the kobjects we have registered. We need to
50 * transpose back from a "default" kobject to our custom struct foo_obj and
51 * then call the show function for that specific object.
52 */
53static ssize_t foo_attr_show(struct kobject *kobj,
54 struct attribute *attr,
55 char *buf)
56{
57 const struct foo_attribute *attribute;
58 struct foo_obj *foo;
59
60 attribute = to_foo_attr(attr);
61 foo = to_foo_obj(kobj);
62
63 if (!attribute->show)
64 return -EIO;
65
66 return attribute->show(foo, attribute, buf);
67}
68
69/*
70 * Just like the default show function above, but this one is for when the
71 * sysfs "store" is requested (when a value is written to a file.)
72 */
73static ssize_t foo_attr_store(struct kobject *kobj,
74 struct attribute *attr,
75 const char *buf, size_t len)
76{
77 const struct foo_attribute *attribute;
78 struct foo_obj *foo;
79
80 attribute = to_foo_attr(attr);
81 foo = to_foo_obj(kobj);
82
83 if (!attribute->store)
84 return -EIO;
85
86 return attribute->store(foo, attribute, buf, len);
87}
88
89/* Our custom sysfs_ops that we will associate with our ktype later on */
90static const struct sysfs_ops foo_sysfs_ops = {
91 .show = foo_attr_show,
92 .store = foo_attr_store,
93};
94
95/*
96 * The release function for our object. This is REQUIRED by the kernel to
97 * have. We free the memory held in our object here.
98 *
99 * NEVER try to get away with just a "blank" release function to try to be
100 * smarter than the kernel. Turns out, no one ever is...
101 */
102static void foo_release(struct kobject *kobj)
103{
104 struct foo_obj *foo;
105
106 foo = to_foo_obj(kobj);
107 kfree(foo);
108}
109
110/*
111 * The "foo" file where the .foo variable is read from and written to.
112 */
113static ssize_t foo_show(struct foo_obj *foo_obj, const struct foo_attribute *attr,
114 char *buf)
115{
116 return sysfs_emit(buf, "%d\n", foo_obj->foo);
117}
118
119static ssize_t foo_store(struct foo_obj *foo_obj, const struct foo_attribute *attr,
120 const char *buf, size_t count)
121{
122 int ret;
123
124 ret = kstrtoint(buf, 10, &foo_obj->foo);
125 if (ret < 0)
126 return ret;
127
128 return count;
129}
130
131/* Sysfs attributes cannot be world-writable. */
132static const struct foo_attribute foo_attribute =
133 __ATTR(foo, 0664, foo_show, foo_store);
134
135/*
136 * More complex function where we determine which variable is being accessed by
137 * looking at the attribute for the "baz" and "bar" files.
138 */
139static ssize_t b_show(struct foo_obj *foo_obj, const struct foo_attribute *attr,
140 char *buf)
141{
142 int var;
143
144 if (strcmp(attr->attr.name, "baz") == 0)
145 var = foo_obj->baz;
146 else
147 var = foo_obj->bar;
148 return sysfs_emit(buf, "%d\n", var);
149}
150
151static ssize_t b_store(struct foo_obj *foo_obj, const struct foo_attribute *attr,
152 const char *buf, size_t count)
153{
154 int var, ret;
155
156 ret = kstrtoint(buf, 10, &var);
157 if (ret < 0)
158 return ret;
159
160 if (strcmp(attr->attr.name, "baz") == 0)
161 foo_obj->baz = var;
162 else
163 foo_obj->bar = var;
164 return count;
165}
166
167static const struct foo_attribute baz_attribute =
168 __ATTR(baz, 0664, b_show, b_store);
169static const struct foo_attribute bar_attribute =
170 __ATTR(bar, 0664, b_show, b_store);
171
172/*
173 * Create a group of attributes so that we can create and destroy them all
174 * at once.
175 */
176static const struct attribute *const foo_default_attrs[] = {
177 &foo_attribute.attr,
178 &baz_attribute.attr,
179 &bar_attribute.attr,
180 NULL, /* need to NULL terminate the list of attributes */
181};
182
183static umode_t foo_default_attrs_is_visible(struct kobject *kobj,
184 const struct attribute *attr,
185 int n)
186{
187 /* Hide attributes with the same name as the kobject. */
188 if (strcmp(kobject_name(kobj), attr->name) == 0)
189 return 0;
190 return attr->mode;
191}
192
193static const struct attribute_group foo_default_group = {
194 .attrs_const = foo_default_attrs,
195 .is_visible_const = foo_default_attrs_is_visible,
196};
197__ATTRIBUTE_GROUPS(foo_default);
198
199/*
200 * Our own ktype for our kobjects. Here we specify our sysfs ops, the
201 * release function, and the set of default attributes we want created
202 * whenever a kobject of this type is registered with the kernel.
203 */
204static const struct kobj_type foo_ktype = {
205 .sysfs_ops = &foo_sysfs_ops,
206 .release = foo_release,
207 .default_groups = foo_default_groups,
208};
209
210static struct kset *example_kset;
211static struct foo_obj *foo_obj;
212static struct foo_obj *bar_obj;
213static struct foo_obj *baz_obj;
214
215static struct foo_obj *create_foo_obj(const char *name)
216{
217 struct foo_obj *foo;
218 int retval;
219
220 /* allocate the memory for the whole object */
221 foo = kzalloc(sizeof(*foo), GFP_KERNEL);
222 if (!foo)
223 return NULL;
224
225 /*
226 * As we have a kset for this kobject, we need to set it before calling
227 * the kobject core.
228 */
229 foo->kobj.kset = example_kset;
230
231 /*
232 * Initialize and add the kobject to the kernel. All the default files
233 * will be created here. As we have already specified a kset for this
234 * kobject, we don't have to set a parent for the kobject, the kobject
235 * will be placed beneath that kset automatically.
236 */
237 retval = kobject_init_and_add(&foo->kobj, &foo_ktype, NULL, "%s", name);
238 if (retval) {
239 kobject_put(&foo->kobj);
240 return NULL;
241 }
242
243 /*
244 * We are always responsible for sending the uevent that the kobject
245 * was added to the system.
246 */
247 kobject_uevent(&foo->kobj, KOBJ_ADD);
248
249 return foo;
250}
251
252static void destroy_foo_obj(struct foo_obj *foo)
253{
254 kobject_put(&foo->kobj);
255}
256
257static int __init example_init(void)
258{
259 /*
260 * Create a kset with the name of "kset_example",
261 * located under /sys/kernel/
262 */
263 example_kset = kset_create_and_add("kset_example", NULL, kernel_kobj);
264 if (!example_kset)
265 return -ENOMEM;
266
267 /*
268 * Create three objects and register them with our kset
269 */
270 foo_obj = create_foo_obj("foo");
271 if (!foo_obj)
272 goto foo_error;
273
274 bar_obj = create_foo_obj("bar");
275 if (!bar_obj)
276 goto bar_error;
277
278 baz_obj = create_foo_obj("baz");
279 if (!baz_obj)
280 goto baz_error;
281
282 return 0;
283
284baz_error:
285 destroy_foo_obj(bar_obj);
286bar_error:
287 destroy_foo_obj(foo_obj);
288foo_error:
289 kset_unregister(example_kset);
290 return -EINVAL;
291}
292
293static void __exit example_exit(void)
294{
295 destroy_foo_obj(baz_obj);
296 destroy_foo_obj(bar_obj);
297 destroy_foo_obj(foo_obj);
298 kset_unregister(example_kset);
299}
300
301module_init(example_init);
302module_exit(example_exit);
303MODULE_DESCRIPTION("Sample kset and ktype implementation");
304MODULE_LICENSE("GPL v2");
305MODULE_AUTHOR("Greg Kroah-Hartman <[email protected]>");