LXR linux/samples/kobject/kobject-example.c

   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        int ret;
  40
  41        ret = kstrtoint(buf, 10, &foo);
  42        if (ret < 0)
  43                return ret;
  44
  45        return count;
  46}
  47
  48/* Sysfs attributes cannot be world-writable. */
  49static struct kobj_attribute foo_attribute =
  50        __ATTR(foo, 0664, foo_show, foo_store);
  51
  52/*
  53 * More complex function where we determine which variable is being accessed by
  54 * looking at the attribute for the "baz" and "bar" files.
  55 */
  56static ssize_t b_show(struct kobject *kobj, struct kobj_attribute *attr,
  57                      char *buf)
  58{
  59        int var;
  60
  61        if (strcmp(attr->attr.name, "baz") == 0)
  62                var = baz;
  63        else
  64                var = bar;
  65        return sprintf(buf, "%d\n", var);
  66}
  67
  68static ssize_t b_store(struct kobject *kobj, struct kobj_attribute *attr,
  69                       const char *buf, size_t count)
  70{
  71        int var, ret;
  72
  73        ret = kstrtoint(buf, 10, &var);
  74        if (ret < 0)
  75                return ret;
  76
  77        if (strcmp(attr->attr.name, "baz") == 0)
  78                baz = var;
  79        else
  80                bar = var;
  81        return count;
  82}
  83
  84static struct kobj_attribute baz_attribute =
  85        __ATTR(baz, 0664, b_show, b_store);
  86static struct kobj_attribute bar_attribute =
  87        __ATTR(bar, 0664, b_show, b_store);
  88
  89
  90/*
  91 * Create a group of attributes so that we can create and destroy them all
  92 * at once.
  93 */
  94static struct attribute *attrs[] = {
  95        &foo_attribute.attr,
  96        &baz_attribute.attr,
  97        &bar_attribute.attr,
  98        NULL,   /* need to NULL terminate the list of attributes */
  99};
 100
 101/*
 102 * An unnamed attribute group will put all of the attributes directly in
 103 * the kobject directory.  If we specify a name, a subdirectory will be
 104 * created for the attributes with the directory being the name of the
 105 * attribute group.
 106 */
 107static struct attribute_group attr_group = {
 108        .attrs = attrs,
 109};
 110
 111static struct kobject *example_kobj;
 112
 113static int __init example_init(void)
 114{
 115        int retval;
 116
 117        /*
 118         * Create a simple kobject with the name of "kobject_example",
 119         * located under /sys/kernel/
 120         *
 121         * As this is a simple directory, no uevent will be sent to
 122         * userspace.  That is why this function should not be used for
 123         * any type of dynamic kobjects, where the name and number are
 124         * not known ahead of time.
 125         */
 126        example_kobj = kobject_create_and_add("kobject_example", kernel_kobj);
 127        if (!example_kobj)
 128                return -ENOMEM;
 129
 130        /* Create the files associated with this kobject */
 131        retval = sysfs_create_group(example_kobj, &attr_group);
 132        if (retval)
 133                kobject_put(example_kobj);
 134
 135        return retval;
 136}
 137
 138static void __exit example_exit(void)
 139{
 140        kobject_put(example_kobj);
 141}
 142
 143module_init(example_init);
 144module_exit(example_exit);
 145MODULE_LICENSE("GPL v2");
 146MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>");
 147