samples/kobject/kset-example.c

   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                 kfree(foo);
 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>");