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  */
foo_attr_show(struct kobject * kobj,struct attribute * attr,char * buf)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  */
foo_attr_store(struct kobject * kobj,struct attribute * attr,const char * buf,size_t len)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  */
foo_release(struct kobject * kobj)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  */
foo_show(struct foo_obj * foo_obj,struct foo_attribute * attr,char * buf)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 
foo_store(struct foo_obj * foo_obj,struct foo_attribute * attr,const char * buf,size_t count)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  */
b_show(struct foo_obj * foo_obj,struct foo_attribute * attr,char * buf)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 
b_store(struct foo_obj * foo_obj,struct foo_attribute * attr,const char * buf,size_t count)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 
create_foo_obj(const char * name)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 
destroy_foo_obj(struct foo_obj * foo)236 static void destroy_foo_obj(struct foo_obj *foo)
237 {
238 	kobject_put(&foo->kobj);
239 }
240 
example_init(void)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 
example_exit(void)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_LICENSE("GPL v2");
288 MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>");
289