linux/samples/kobject/kobject-example.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Sample kobject implementation
 *
 * Copyright (C) 2004-2007 Greg Kroah-Hartman <[email protected]>
 * Copyright (C) 2007 Novell Inc.
 */
#include <linux/kobject.h>
#include <linux/string.h>
#include <linux/sysfs.h>
#include <linux/module.h>
#include <linux/init.h>

/*
 * This module shows how to create a simple subdirectory in sysfs called
 * /sys/kernel/kobject-example  In that directory, 3 files are created:
 * "foo", "baz", and "bar".  If an integer is written to these files, it can be
 * later read out of it.
 */

static int foo;
static int baz;
static int bar;

/*
 * The "foo" file where a static variable is read from and written to.
 */
static ssize_t foo_show(struct kobject *kobj, struct kobj_attribute *attr,
			char *buf)
{ … }

static ssize_t foo_store(struct kobject *kobj, struct kobj_attribute *attr,
			 const char *buf, size_t count)
{ … }

/* Sysfs attributes cannot be world-writable. */
static struct kobj_attribute foo_attribute = …;

/*
 * More complex function where we determine which variable is being accessed by
 * looking at the attribute for the "baz" and "bar" files.
 */
static ssize_t b_show(struct kobject *kobj, struct kobj_attribute *attr,
		      char *buf)
{ … }

static ssize_t b_store(struct kobject *kobj, struct kobj_attribute *attr,
		       const char *buf, size_t count)
{ … }

static struct kobj_attribute baz_attribute = …;
static struct kobj_attribute bar_attribute = …;


/*
 * Create a group of attributes so that we can create and destroy them all
 * at once.
 */
static struct attribute *attrs[] = …;

/*
 * An unnamed attribute group will put all of the attributes directly in
 * the kobject directory.  If we specify a name, a subdirectory will be
 * created for the attributes with the directory being the name of the
 * attribute group.
 */
static struct attribute_group attr_group = …;

static struct kobject *example_kobj;

static int __init example_init(void)
{ … }

static void __exit example_exit(void)
{ … }

module_init(…) …;
module_exit(example_exit);
MODULE_DESCRIPTION(…) …;
MODULE_LICENSE(…) …;
MODULE_AUTHOR(…) …;