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  */
31 struct 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. */
40 struct 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  */
54 static 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  */
74 static 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 */
91 static 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  */
103 static 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  */
114 static 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 
120 static ssize_t foo_store(struct foo_obj *foo_obj, struct foo_attribute *attr,
121 			 const char *buf, size_t count)
122 {
123 	int ret;
124 
125 	ret = kstrtoint(buf, 10, &foo_obj->foo);
126 	if (ret < 0)
127 		return ret;
128 
129 	return count;
130 }
131 
132 /* Sysfs attributes cannot be world-writable. */
133 static struct foo_attribute foo_attribute =
134 	__ATTR(foo, 0664, foo_show, foo_store);
135 
136 /*
137  * More complex function where we determine which variable is being accessed by
138  * looking at the attribute for the "baz" and "bar" files.
139  */
140 static ssize_t b_show(struct foo_obj *foo_obj, struct foo_attribute *attr,
141 		      char *buf)
142 {
143 	int var;
144 
145 	if (strcmp(attr->attr.name, "baz") == 0)
146 		var = foo_obj->baz;
147 	else
148 		var = foo_obj->bar;
149 	return sprintf(buf, "%d\n", var);
150 }
151 
152 static ssize_t b_store(struct foo_obj *foo_obj, struct foo_attribute *attr,
153 		       const char *buf, size_t count)
154 {
155 	int var, ret;
156 
157 	ret = kstrtoint(buf, 10, &var);
158 	if (ret < 0)
159 		return ret;
160 
161 	if (strcmp(attr->attr.name, "baz") == 0)
162 		foo_obj->baz = var;
163 	else
164 		foo_obj->bar = var;
165 	return count;
166 }
167 
168 static struct foo_attribute baz_attribute =
169 	__ATTR(baz, 0664, b_show, b_store);
170 static struct foo_attribute bar_attribute =
171 	__ATTR(bar, 0664, b_show, b_store);
172 
173 /*
174  * Create a group of attributes so that we can create and destroy them all
175  * at once.
176  */
177 static struct attribute *foo_default_attrs[] = {
178 	&foo_attribute.attr,
179 	&baz_attribute.attr,
180 	&bar_attribute.attr,
181 	NULL,	/* need to NULL terminate the list of attributes */
182 };
183 
184 /*
185  * Our own ktype for our kobjects.  Here we specify our sysfs ops, the
186  * release function, and the set of default attributes we want created
187  * whenever a kobject of this type is registered with the kernel.
188  */
189 static struct kobj_type foo_ktype = {
190 	.sysfs_ops = &foo_sysfs_ops,
191 	.release = foo_release,
192 	.default_attrs = foo_default_attrs,
193 };
194 
195 static struct kset *example_kset;
196 static struct foo_obj *foo_obj;
197 static struct foo_obj *bar_obj;
198 static struct foo_obj *baz_obj;
199 
200 static struct foo_obj *create_foo_obj(const char *name)
201 {
202 	struct foo_obj *foo;
203 	int retval;
204 
205 	/* allocate the memory for the whole object */
206 	foo = kzalloc(sizeof(*foo), GFP_KERNEL);
207 	if (!foo)
208 		return NULL;
209 
210 	/*
211 	 * As we have a kset for this kobject, we need to set it before calling
212 	 * the kobject core.
213 	 */
214 	foo->kobj.kset = example_kset;
215 
216 	/*
217 	 * Initialize and add the kobject to the kernel.  All the default files
218 	 * will be created here.  As we have already specified a kset for this
219 	 * kobject, we don't have to set a parent for the kobject, the kobject
220 	 * will be placed beneath that kset automatically.
221 	 */
222 	retval = kobject_init_and_add(&foo->kobj, &foo_ktype, NULL, "%s", name);
223 	if (retval) {
224 		kobject_put(&foo->kobj);
225 		return NULL;
226 	}
227 
228 	/*
229 	 * We are always responsible for sending the uevent that the kobject
230 	 * was added to the system.
231 	 */
232 	kobject_uevent(&foo->kobj, KOBJ_ADD);
233 
234 	return foo;
235 }
236 
237 static void destroy_foo_obj(struct foo_obj *foo)
238 {
239 	kobject_put(&foo->kobj);
240 }
241 
242 static int __init example_init(void)
243 {
244 	/*
245 	 * Create a kset with the name of "kset_example",
246 	 * located under /sys/kernel/
247 	 */
248 	example_kset = kset_create_and_add("kset_example", NULL, kernel_kobj);
249 	if (!example_kset)
250 		return -ENOMEM;
251 
252 	/*
253 	 * Create three objects and register them with our kset
254 	 */
255 	foo_obj = create_foo_obj("foo");
256 	if (!foo_obj)
257 		goto foo_error;
258 
259 	bar_obj = create_foo_obj("bar");
260 	if (!bar_obj)
261 		goto bar_error;
262 
263 	baz_obj = create_foo_obj("baz");
264 	if (!baz_obj)
265 		goto baz_error;
266 
267 	return 0;
268 
269 baz_error:
270 	destroy_foo_obj(bar_obj);
271 bar_error:
272 	destroy_foo_obj(foo_obj);
273 foo_error:
274 	kset_unregister(example_kset);
275 	return -EINVAL;
276 }
277 
278 static void __exit example_exit(void)
279 {
280 	destroy_foo_obj(baz_obj);
281 	destroy_foo_obj(bar_obj);
282 	destroy_foo_obj(foo_obj);
283 	kset_unregister(example_kset);
284 }
285 
286 module_init(example_init);
287 module_exit(example_exit);
288 MODULE_LICENSE("GPL v2");
289 MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>");
290