kset-example.c

  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 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 <greg@kroah.com>");