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/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         sscanf(buf, "%du", &foo_obj->foo);
 124         return count;
 125 }
 126
 127 /* Sysfs attributes cannot be world-writable. */
 128 static struct foo_attribute foo_attribute =
 129         __ATTR(foo, 0664, foo_show, foo_store);
 130
 131 /*
 132  * More complex function where we determine which variable is being accessed by
 133  * looking at the attribute for the "baz" and "bar" files.
 134  */
 135 static ssize_t b_show(struct foo_obj *foo_obj, struct foo_attribute *attr,
 136                       char *buf)
 137 {
 138         int var;
 139
 140         if (strcmp(attr->attr.name, "baz") == 0)
 141                 var = foo_obj->baz;
 142         else
 143                 var = foo_obj->bar;
 144         return sprintf(buf, "%d\n", var);
 145 }
 146
 147 static ssize_t b_store(struct foo_obj *foo_obj, struct foo_attribute *attr,
 148                        const char *buf, size_t count)
 149 {
 150         int var;
 151
 152         sscanf(buf, "%du", &var);
 153         if (strcmp(attr->attr.name, "baz") == 0)
 154                 foo_obj->baz = var;
 155         else
 156                 foo_obj->bar = var;
 157         return count;
 158 }
 159
 160 static struct foo_attribute baz_attribute =
 161         __ATTR(baz, 0664, b_show, b_store);
 162 static struct foo_attribute bar_attribute =
 163         __ATTR(bar, 0664, b_show, b_store);
 164
 165 /*
 166  * Create a group of attributes so that we can create and destroy them all
 167  * at once.
 168  */
 169 static struct attribute *foo_default_attrs[] = {
 170         &foo_attribute.attr,
 171         &baz_attribute.attr,
 172         &bar_attribute.attr,
 173         NULL,   /* need to NULL terminate the list of attributes */
 174 };
 175
 176 /*
 177  * Our own ktype for our kobjects.  Here we specify our sysfs ops, the
 178  * release function, and the set of default attributes we want created
 179  * whenever a kobject of this type is registered with the kernel.
 180  */
 181 static struct kobj_type foo_ktype = {
 182         .sysfs_ops = &foo_sysfs_ops,
 183         .release = foo_release,
 184         .default_attrs = foo_default_attrs,
 185 };
 186
 187 static struct kset *example_kset;
 188 static struct foo_obj *foo_obj;
 189 static struct foo_obj *bar_obj;
 190 static struct foo_obj *baz_obj;
 191
 192 static struct foo_obj *create_foo_obj(const char *name)
 193 {
 194         struct foo_obj *foo;
 195         int retval;
 196
 197         /* allocate the memory for the whole object */
 198         foo = kzalloc(sizeof(*foo), GFP_KERNEL);
 199         if (!foo)
 200                 return NULL;
 201
 202         /*
 203          * As we have a kset for this kobject, we need to set it before calling
 204          * the kobject core.
 205          */
 206         foo->kobj.kset = example_kset;
 207
 208         /*
 209          * Initialize and add the kobject to the kernel.  All the default files
 210          * will be created here.  As we have already specified a kset for this
 211          * kobject, we don't have to set a parent for the kobject, the kobject
 212          * will be placed beneath that kset automatically.
 213          */
 214         retval = kobject_init_and_add(&foo->kobj, &foo_ktype, NULL, "%s", name);
 215         if (retval) {
 216                 kobject_put(&foo->kobj);
 217                 return NULL;
 218         }
 219
 220         /*
 221          * We are always responsible for sending the uevent that the kobject
 222          * was added to the system.
 223          */
 224         kobject_uevent(&foo->kobj, KOBJ_ADD);
 225
 226         return foo;
 227 }
 228
 229 static void destroy_foo_obj(struct foo_obj *foo)
 230 {
 231         kobject_put(&foo->kobj);
 232 }
 233
 234 static int __init example_init(void)
 235 {
 236         /*
 237          * Create a kset with the name of "kset_example",
 238          * located under /sys/kernel/
 239          */
 240         example_kset = kset_create_and_add("kset_example", NULL, kernel_kobj);
 241         if (!example_kset)
 242                 return -ENOMEM;
 243
 244         /*
 245          * Create three objects and register them with our kset
 246          */
 247         foo_obj = create_foo_obj("foo");
 248         if (!foo_obj)
 249                 goto foo_error;
 250
 251         bar_obj = create_foo_obj("bar");
 252         if (!bar_obj)
 253                 goto bar_error;
 254
 255         baz_obj = create_foo_obj("baz");
 256         if (!baz_obj)
 257                 goto baz_error;
 258
 259         return 0;
 260
 261 baz_error:
 262         destroy_foo_obj(bar_obj);
 263 bar_error:
 264         destroy_foo_obj(foo_obj);
 265 foo_error:
 266         kset_unregister(example_kset);
 267         return -EINVAL;
 268 }
 269
 270 static void __exit example_exit(void)
 271 {
 272         destroy_foo_obj(baz_obj);
 273         destroy_foo_obj(bar_obj);
 274         destroy_foo_obj(foo_obj);
 275         kset_unregister(example_kset);
 276 }
 277
 278 module_init(example_init);
 279 module_exit(example_exit);
 280 MODULE_LICENSE("GPL");
 281 MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>");