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Linux/samples/kobject/kset-example.c

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  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  */
 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  */
 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  */
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  */
112 static ssize_t foo_show(struct foo_obj *foo_obj, struct foo_attribute *attr,
113                         char *buf)
114 {
115         return sprintf(buf, "%d\n", foo_obj->foo);
116 }
117 
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  */
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 sprintf(buf, "%d\n", var);
148 }
149 
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 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 
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 
236 static void destroy_foo_obj(struct foo_obj *foo)
237 {
238         kobject_put(&foo->kobj);
239 }
240 
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 
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 

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