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/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 */
  30struct 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. */
  39struct 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 */
  53static 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 */
  73static 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 */
  90static 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 */
 102static 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 */
 113static 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
 119static 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
 126static 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 */
 133static 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
 145static 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
 158static struct foo_attribute baz_attribute =
 159        __ATTR(baz, 0666, b_show, b_store);
 160static 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 */
 167static 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 */
 179static struct kobj_type foo_ktype = {
 180        .sysfs_ops = &foo_sysfs_ops,
 181        .release = foo_release,
 182        .default_attrs = foo_default_attrs,
 183};
 184
 185static struct kset *example_kset;
 186static struct foo_obj *foo_obj;
 187static struct foo_obj *bar_obj;
 188static struct foo_obj *baz_obj;
 189
 190static 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
 227static void destroy_foo_obj(struct foo_obj *foo)
 228{
 229        kobject_put(&foo->kobj);
 230}
 231
 232static 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
 259baz_error:
 260        destroy_foo_obj(bar_obj);
 261bar_error:
 262        destroy_foo_obj(foo_obj);
 263foo_error:
 264        return -EINVAL;
 265}
 266
 267static 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
 275module_init(example_init);
 276module_exit(example_exit);
 277MODULE_LICENSE("GPL");
 278MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>");
 279
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