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

   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * Sample kobject implementation
   4 *
   5 * Copyright (C) 2004-2007 Greg Kroah-Hartman <greg@kroah.com>
   6 * Copyright (C) 2007 Novell Inc.
   7 */
   8#include <linux/kobject.h>
   9#include <linux/string.h>
  10#include <linux/sysfs.h>
  11#include <linux/module.h>
  12#include <linux/init.h>
  13
  14/*
  15 * This module shows how to create a simple subdirectory in sysfs called
  16 * /sys/kernel/kobject-example  In that directory, 3 files are created:
  17 * "foo", "baz", and "bar".  If an integer is written to these files, it can be
  18 * later read out of it.
  19 */
  20
  21static int foo;
  22static int baz;
  23static int bar;
  24
  25/*
  26 * The "foo" file where a static variable is read from and written to.
  27 */
  28static ssize_t foo_show(struct kobject *kobj, struct kobj_attribute *attr,
  29                        char *buf)
  30{
  31        return sprintf(buf, "%d\n", foo);
  32}
  33
  34static ssize_t foo_store(struct kobject *kobj, struct kobj_attribute *attr,
  35                         const char *buf, size_t count)
  36{
  37        int ret;
  38
  39        ret = kstrtoint(buf, 10, &foo);
  40        if (ret < 0)
  41                return ret;
  42
  43        return count;
  44}
  45
  46/* Sysfs attributes cannot be world-writable. */
  47static struct kobj_attribute foo_attribute =
  48        __ATTR(foo, 0664, foo_show, foo_store);
  49
  50/*
  51 * More complex function where we determine which variable is being accessed by
  52 * looking at the attribute for the "baz" and "bar" files.
  53 */
  54static ssize_t b_show(struct kobject *kobj, struct kobj_attribute *attr,
  55                      char *buf)
  56{
  57        int var;
  58
  59        if (strcmp(attr->attr.name, "baz") == 0)
  60                var = baz;
  61        else
  62                var = bar;
  63        return sprintf(buf, "%d\n", var);
  64}
  65
  66static ssize_t b_store(struct kobject *kobj, struct kobj_attribute *attr,
  67                       const char *buf, size_t count)
  68{
  69        int var, ret;
  70
  71        ret = kstrtoint(buf, 10, &var);
  72        if (ret < 0)
  73                return ret;
  74
  75        if (strcmp(attr->attr.name, "baz") == 0)
  76                baz = var;
  77        else
  78                bar = var;
  79        return count;
  80}
  81
  82static struct kobj_attribute baz_attribute =
  83        __ATTR(baz, 0664, b_show, b_store);
  84static struct kobj_attribute bar_attribute =
  85        __ATTR(bar, 0664, b_show, b_store);
  86
  87
  88/*
  89 * Create a group of attributes so that we can create and destroy them all
  90 * at once.
  91 */
  92static struct attribute *attrs[] = {
  93        &foo_attribute.attr,
  94        &baz_attribute.attr,
  95        &bar_attribute.attr,
  96        NULL,   /* need to NULL terminate the list of attributes */
  97};
  98
  99/*
 100 * An unnamed attribute group will put all of the attributes directly in
 101 * the kobject directory.  If we specify a name, a subdirectory will be
 102 * created for the attributes with the directory being the name of the
 103 * attribute group.
 104 */
 105static struct attribute_group attr_group = {
 106        .attrs = attrs,
 107};
 108
 109static struct kobject *example_kobj;
 110
 111static int __init example_init(void)
 112{
 113        int retval;
 114
 115        /*
 116         * Create a simple kobject with the name of "kobject_example",
 117         * located under /sys/kernel/
 118         *
 119         * As this is a simple directory, no uevent will be sent to
 120         * userspace.  That is why this function should not be used for
 121         * any type of dynamic kobjects, where the name and number are
 122         * not known ahead of time.
 123         */
 124        example_kobj = kobject_create_and_add("kobject_example", kernel_kobj);
 125        if (!example_kobj)
 126                return -ENOMEM;
 127
 128        /* Create the files associated with this kobject */
 129        retval = sysfs_create_group(example_kobj, &attr_group);
 130        if (retval)
 131                kobject_put(example_kobj);
 132
 133        return retval;
 134}
 135
 136static void __exit example_exit(void)
 137{
 138        kobject_put(example_kobj);
 139}
 140
 141module_init(example_init);
 142module_exit(example_exit);
 143MODULE_LICENSE("GPL v2");
 144MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>");
 145