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 */
  31struct 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. */
  40struct 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 */
  54static 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 */
  74static 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 */
  91static 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 */
 103static 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 */
 114static 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
 120static 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
 127static struct foo_attribute foo_attribute =
 128        __ATTR(foo, 0666, foo_show, foo_store);
 129
 130/*
 131 * More complex function where we determine which variable is being accessed by
 132 * looking at the attribute for the "baz" and "bar" files.
 133 */
 134static ssize_t b_show(struct foo_obj *foo_obj, struct foo_attribute *attr,
 135                      char *buf)
 136{
 137        int var;
 138
 139        if (strcmp(attr->attr.name, "baz") == 0)
 140                var = foo_obj->baz;
 141        else
 142                var = foo_obj->bar;
 143        return sprintf(buf, "%d\n", var);
 144}
 145
 146static ssize_t b_store(struct foo_obj *foo_obj, struct foo_attribute *attr,
 147                       const char *buf, size_t count)
 148{
 149        int var;
 150
 151        sscanf(buf, "%du", &var);
 152        if (strcmp(attr->attr.name, "baz") == 0)
 153                foo_obj->baz = var;
 154        else
 155                foo_obj->bar = var;
 156        return count;
 157}
 158
 159static struct foo_attribute baz_attribute =
 160        __ATTR(baz, 0666, b_show, b_store);
 161static struct foo_attribute bar_attribute =
 162        __ATTR(bar, 0666, b_show, b_store);
 163
 164/*
 165 * Create a group of attributes so that we can create and destroy them all
 166 * at once.
 167 */
 168static struct attribute *foo_default_attrs[] = {
 169        &foo_attribute.attr,
 170        &baz_attribute.attr,
 171        &bar_attribute.attr,
 172        NULL,   /* need to NULL terminate the list of attributes */
 173};
 174
 175/*
 176 * Our own ktype for our kobjects.  Here we specify our sysfs ops, the
 177 * release function, and the set of default attributes we want created
 178 * whenever a kobject of this type is registered with the kernel.
 179 */
 180static struct kobj_type foo_ktype = {
 181        .sysfs_ops = &foo_sysfs_ops,
 182        .release = foo_release,
 183        .default_attrs = foo_default_attrs,
 184};
 185
 186static struct kset *example_kset;
 187static struct foo_obj *foo_obj;
 188static struct foo_obj *bar_obj;
 189static struct foo_obj *baz_obj;
 190
 191static struct foo_obj *create_foo_obj(const char *name)
 192{
 193        struct foo_obj *foo;
 194        int retval;
 195
 196        /* allocate the memory for the whole object */
 197        foo = kzalloc(sizeof(*foo), GFP_KERNEL);
 198        if (!foo)
 199                return NULL;
 200
 201        /*
 202         * As we have a kset for this kobject, we need to set it before calling
 203         * the kobject core.
 204         */
 205        foo->kobj.kset = example_kset;
 206
 207        /*
 208         * Initialize and add the kobject to the kernel.  All the default files
 209         * will be created here.  As we have already specified a kset for this
 210         * kobject, we don't have to set a parent for the kobject, the kobject
 211         * will be placed beneath that kset automatically.
 212         */
 213        retval = kobject_init_and_add(&foo->kobj, &foo_ktype, NULL, "%s", name);
 214        if (retval) {
 215                kobject_put(&foo->kobj);
 216                return NULL;
 217        }
 218
 219        /*
 220         * We are always responsible for sending the uevent that the kobject
 221         * was added to the system.
 222         */
 223        kobject_uevent(&foo->kobj, KOBJ_ADD);
 224
 225        return foo;
 226}
 227
 228static void destroy_foo_obj(struct foo_obj *foo)
 229{
 230        kobject_put(&foo->kobj);
 231}
 232
 233static int __init example_init(void)
 234{
 235        /*
 236         * Create a kset with the name of "kset_example",
 237         * located under /sys/kernel/
 238         */
 239        example_kset = kset_create_and_add("kset_example", NULL, kernel_kobj);
 240        if (!example_kset)
 241                return -ENOMEM;
 242
 243        /*
 244         * Create three objects and register them with our kset
 245         */
 246        foo_obj = create_foo_obj("foo");
 247        if (!foo_obj)
 248                goto foo_error;
 249
 250        bar_obj = create_foo_obj("bar");
 251        if (!bar_obj)
 252                goto bar_error;
 253
 254        baz_obj = create_foo_obj("baz");
 255        if (!baz_obj)
 256                goto baz_error;
 257
 258        return 0;
 259
 260baz_error:
 261        destroy_foo_obj(bar_obj);
 262bar_error:
 263        destroy_foo_obj(foo_obj);
 264foo_error:
 265        return -EINVAL;
 266}
 267
 268static void __exit example_exit(void)
 269{
 270        destroy_foo_obj(baz_obj);
 271        destroy_foo_obj(bar_obj);
 272        destroy_foo_obj(foo_obj);
 273        kset_unregister(example_kset);
 274}
 275
 276module_init(example_init);
 277module_exit(example_exit);
 278MODULE_LICENSE("GPL");
 279MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>");
 280
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