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