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/module.h>
14 #include <linux/init.h>
15 
16 /*
17  * This module shows how to create a kset in sysfs called
18  * /sys/kernel/kset-example
19  * Then tree kobjects are created and assigned to this kset, "foo", "baz",
20  * and "bar".  In those kobjects, attributes of the same name are also
21  * created and if an integer is written to these files, it can be later
22  * read out of it.
23  */
24 
25 
26 /*
27  * This is our "object" that we will create a few of and register them with
28  * sysfs.
29  */
30 struct foo_obj {
31 	struct kobject kobj;
32 	int foo;
33 	int baz;
34 	int bar;
35 };
36 #define to_foo_obj(x) container_of(x, struct foo_obj, kobj)
37 
38 /* a custom attribute that works just for a struct foo_obj. */
39 struct foo_attribute {
40 	struct attribute attr;
41 	ssize_t (*show)(struct foo_obj *foo, struct foo_attribute *attr, char *buf);
42 	ssize_t (*store)(struct foo_obj *foo, struct foo_attribute *attr, const char *buf, size_t count);
43 };
44 #define to_foo_attr(x) container_of(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  */
53 static ssize_t foo_attr_show(struct kobject *kobj,
54 			     struct attribute *attr,
55 			     char *buf)
56 {
57 	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  */
73 static ssize_t foo_attr_store(struct kobject *kobj,
74 			      struct attribute *attr,
75 			      const char *buf, size_t len)
76 {
77 	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 */
90 static 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  */
102 static 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  */
113 static ssize_t foo_show(struct foo_obj *foo_obj, struct foo_attribute *attr,
114 			char *buf)
115 {
116 	return sprintf(buf, "%d\n", foo_obj->foo);
117 }
118 
119 static ssize_t foo_store(struct foo_obj *foo_obj, struct foo_attribute *attr,
120 			 const char *buf, size_t count)
121 {
122 	sscanf(buf, "%du", &foo_obj->foo);
123 	return count;
124 }
125 
126 static struct foo_attribute foo_attribute =
127 	__ATTR(foo, 0666, foo_show, foo_store);
128 
129 /*
130  * More complex function where we determine which varible is being accessed by
131  * looking at the attribute for the "baz" and "bar" files.
132  */
133 static ssize_t b_show(struct foo_obj *foo_obj, struct foo_attribute *attr,
134 		      char *buf)
135 {
136 	int var;
137 
138 	if (strcmp(attr->attr.name, "baz") == 0)
139 		var = foo_obj->baz;
140 	else
141 		var = foo_obj->bar;
142 	return sprintf(buf, "%d\n", var);
143 }
144 
145 static ssize_t b_store(struct foo_obj *foo_obj, struct foo_attribute *attr,
146 		       const char *buf, size_t count)
147 {
148 	int var;
149 
150 	sscanf(buf, "%du", &var);
151 	if (strcmp(attr->attr.name, "baz") == 0)
152 		foo_obj->baz = var;
153 	else
154 		foo_obj->bar = var;
155 	return count;
156 }
157 
158 static struct foo_attribute baz_attribute =
159 	__ATTR(baz, 0666, b_show, b_store);
160 static struct foo_attribute bar_attribute =
161 	__ATTR(bar, 0666, b_show, b_store);
162 
163 /*
164  * Create a group of attributes so that we can create and destory them all
165  * at once.
166  */
167 static struct attribute *foo_default_attrs[] = {
168 	&foo_attribute.attr,
169 	&baz_attribute.attr,
170 	&bar_attribute.attr,
171 	NULL,	/* need to NULL terminate the list of attributes */
172 };
173 
174 /*
175  * Our own ktype for our kobjects.  Here we specify our sysfs ops, the
176  * release function, and the set of default attributes we want created
177  * whenever a kobject of this type is registered with the kernel.
178  */
179 static struct kobj_type foo_ktype = {
180 	.sysfs_ops = &foo_sysfs_ops,
181 	.release = foo_release,
182 	.default_attrs = foo_default_attrs,
183 };
184 
185 static struct kset *example_kset;
186 static struct foo_obj *foo_obj;
187 static struct foo_obj *bar_obj;
188 static struct foo_obj *baz_obj;
189 
190 static struct foo_obj *create_foo_obj(const char *name)
191 {
192 	struct foo_obj *foo;
193 	int retval;
194 
195 	/* allocate the memory for the whole object */
196 	foo = kzalloc(sizeof(*foo), GFP_KERNEL);
197 	if (!foo)
198 		return NULL;
199 
200 	/*
201 	 * As we have a kset for this kobject, we need to set it before calling
202 	 * the kobject core.
203 	 */
204 	foo->kobj.kset = example_kset;
205 
206 	/*
207 	 * Initialize and add the kobject to the kernel.  All the default files
208 	 * will be created here.  As we have already specified a kset for this
209 	 * kobject, we don't have to set a parent for the kobject, the kobject
210 	 * will be placed beneath that kset automatically.
211 	 */
212 	retval = kobject_init_and_add(&foo->kobj, &foo_ktype, NULL, "%s", name);
213 	if (retval) {
214 		kobject_put(&foo->kobj);
215 		return NULL;
216 	}
217 
218 	/*
219 	 * We are always responsible for sending the uevent that the kobject
220 	 * was added to the system.
221 	 */
222 	kobject_uevent(&foo->kobj, KOBJ_ADD);
223 
224 	return foo;
225 }
226 
227 static void destroy_foo_obj(struct foo_obj *foo)
228 {
229 	kobject_put(&foo->kobj);
230 }
231 
232 static int example_init(void)
233 {
234 	/*
235 	 * Create a kset with the name of "kset_example",
236 	 * located under /sys/kernel/
237 	 */
238 	example_kset = kset_create_and_add("kset_example", NULL, kernel_kobj);
239 	if (!example_kset)
240 		return -ENOMEM;
241 
242 	/*
243 	 * Create three objects and register them with our kset
244 	 */
245 	foo_obj = create_foo_obj("foo");
246 	if (!foo_obj)
247 		goto foo_error;
248 
249 	bar_obj = create_foo_obj("bar");
250 	if (!bar_obj)
251 		goto bar_error;
252 
253 	baz_obj = create_foo_obj("baz");
254 	if (!baz_obj)
255 		goto baz_error;
256 
257 	return 0;
258 
259 baz_error:
260 	destroy_foo_obj(bar_obj);
261 bar_error:
262 	destroy_foo_obj(foo_obj);
263 foo_error:
264 	return -EINVAL;
265 }
266 
267 static void example_exit(void)
268 {
269 	destroy_foo_obj(baz_obj);
270 	destroy_foo_obj(bar_obj);
271 	destroy_foo_obj(foo_obj);
272 	kset_unregister(example_kset);
273 }
274 
275 module_init(example_init);
276 module_exit(example_exit);
277 MODULE_LICENSE("GPL");
278 MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>");
279