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TOMOYO Linux Cross Reference
Linux/samples/kobject/kset-example.c

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  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 

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