linux/samples/kobject/kobject-example.c
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   1/*
   2 * Sample kobject 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 simple subdirectory in sysfs called
  18 * /sys/kernel/kobject-example  In that directory, 3 files are created:
  19 * "foo", "baz", and "bar".  If an integer is written to these files, it can be
  20 * later read out of it.
  21 */
  22
  23static int foo;
  24static int baz;
  25static int bar;
  26
  27/*
  28 * The "foo" file where a static variable is read from and written to.
  29 */
  30static ssize_t foo_show(struct kobject *kobj, struct kobj_attribute *attr,
  31                        char *buf)
  32{
  33        return sprintf(buf, "%d\n", foo);
  34}
  35
  36static ssize_t foo_store(struct kobject *kobj, struct kobj_attribute *attr,
  37                         const char *buf, size_t count)
  38{
  39        sscanf(buf, "%du", &foo);
  40        return count;
  41}
  42
  43static struct kobj_attribute foo_attribute =
  44        __ATTR(foo, 0666, foo_show, foo_store);
  45
  46/*
  47 * More complex function where we determine which variable is being accessed by
  48 * looking at the attribute for the "baz" and "bar" files.
  49 */
  50static ssize_t b_show(struct kobject *kobj, struct kobj_attribute *attr,
  51                      char *buf)
  52{
  53        int var;
  54
  55        if (strcmp(attr->attr.name, "baz") == 0)
  56                var = baz;
  57        else
  58                var = bar;
  59        return sprintf(buf, "%d\n", var);
  60}
  61
  62static ssize_t b_store(struct kobject *kobj, struct kobj_attribute *attr,
  63                       const char *buf, size_t count)
  64{
  65        int var;
  66
  67        sscanf(buf, "%du", &var);
  68        if (strcmp(attr->attr.name, "baz") == 0)
  69                baz = var;
  70        else
  71                bar = var;
  72        return count;
  73}
  74
  75static struct kobj_attribute baz_attribute =
  76        __ATTR(baz, 0666, b_show, b_store);
  77static struct kobj_attribute bar_attribute =
  78        __ATTR(bar, 0666, b_show, b_store);
  79
  80
  81/*
  82 * Create a group of attributes so that we can create and destroy them all
  83 * at once.
  84 */
  85static struct attribute *attrs[] = {
  86        &foo_attribute.attr,
  87        &baz_attribute.attr,
  88        &bar_attribute.attr,
  89        NULL,   /* need to NULL terminate the list of attributes */
  90};
  91
  92/*
  93 * An unnamed attribute group will put all of the attributes directly in
  94 * the kobject directory.  If we specify a name, a subdirectory will be
  95 * created for the attributes with the directory being the name of the
  96 * attribute group.
  97 */
  98static struct attribute_group attr_group = {
  99        .attrs = attrs,
 100};
 101
 102static struct kobject *example_kobj;
 103
 104static int __init example_init(void)
 105{
 106        int retval;
 107
 108        /*
 109         * Create a simple kobject with the name of "kobject_example",
 110         * located under /sys/kernel/
 111         *
 112         * As this is a simple directory, no uevent will be sent to
 113         * userspace.  That is why this function should not be used for
 114         * any type of dynamic kobjects, where the name and number are
 115         * not known ahead of time.
 116         */
 117        example_kobj = kobject_create_and_add("kobject_example", kernel_kobj);
 118        if (!example_kobj)
 119                return -ENOMEM;
 120
 121        /* Create the files associated with this kobject */
 122        retval = sysfs_create_group(example_kobj, &attr_group);
 123        if (retval)
 124                kobject_put(example_kobj);
 125
 126        return retval;
 127}
 128
 129static void __exit example_exit(void)
 130{
 131        kobject_put(example_kobj);
 132}
 133
 134module_init(example_init);
 135module_exit(example_exit);
 136MODULE_LICENSE("GPL");
 137MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>");
 138
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