Linux kernel & device driver programming

Cross-Referenced Linux and Device Driver Code

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Version: [ 2.6.11.8 ] [ 2.6.25 ] [ 2.6.25.8 ] [ 2.6.31.13 ] Architecture: [ i386 ]
  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 __init 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 __exit 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 
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