kobject: add sample code for how to use kobjects in a simple manner.

	help

	  This build markers example modules.

config SAMPLE_KOBJECT

	tristate "Build kobject examples"

	help

	  This config option will allow you to build a number of

	  different kobject sample modules showing how to use kobjects,

	  ksets, and ktypes properly.

	  If in doubt, say "N" here.

endif # SAMPLES

# Makefile for Linux samples code

obj-$(CONFIG_SAMPLES)	+= markers/

obj-$(CONFIG_SAMPLES)	+= markers/ kobject/

obj-$(CONFIG_SAMPLE_KOBJECT) += kobject-example.o

/*

 * Sample kobject implementation

 *

 * Copyright (C) 2004-2007 Greg Kroah-Hartman <greg@kroah.com>

 * Copyright (C) 2007 Novell Inc.

 *

 * Released under the GPL version 2 only.

 *

 */

#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)

{

	return sprintf(buf, "%d\n", foo);

}

static ssize_t foo_store(struct kobject *kobj, struct kobj_attribute *attr,

			 const char *buf, size_t count)

{

	sscanf(buf, "%du", &foo);

	return count;

}

static struct kobj_attribute foo_attribute =

	__ATTR(foo, 0666, foo_show, foo_store);

/*

 * More complex function where we determine which varible 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)

{

	int var;

	if (strcmp(attr->attr.name, "baz") == 0)

		var = baz;

	else

		var = bar;

	return sprintf(buf, "%d\n", var);

}

static ssize_t b_store(struct kobject *kobj, struct kobj_attribute *attr,

		       const char *buf, size_t count)

{

	int var;

	sscanf(buf, "%du", &var);

	if (strcmp(attr->attr.name, "baz") == 0)

		baz = var;

	else

		bar = var;

	return count;

}

static struct kobj_attribute baz_attribute =

	__ATTR(baz, 0666, b_show, b_store);

static struct kobj_attribute bar_attribute =

	__ATTR(bar, 0666, b_show, b_store);

/*

 * Create a group of attributes so that we can create and destory them all

 * at once.

 */

static struct attribute *attrs[] = {

	&foo_attribute.attr,

	&baz_attribute.attr,

	&bar_attribute.attr,

	NULL,	/* need to NULL terminate the list of attributes */

};

/*

 * 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 = {

	.attrs = attrs,

};

static struct kobject *example_kobj;

static int example_init(void)

{

	int retval;

	/*

	 * Create a simple kobject with the name of "kobject_example",

	 * located under /sys/kernel/

	 *

	 * As this is a simple directory, no uevent will be sent to

	 * userspace.  That is why this function should not be used for

	 * any type of dynamic kobjects, where the name and number are

	 * not known ahead of time.

	 */

	example_kobj = kobject_create_and_add("kobject_example", kernel_kobj);

	if (!example_kobj)

		return -ENOMEM;

	/* Create the files associated with this kobject */

	retval = sysfs_create_group(example_kobj, &attr_group);

	if (retval)

		kobject_put(example_kobj);

	return retval;

}

static void example_exit(void)

{

	kobject_put(example_kobj);

}

module_init(example_init);

module_exit(example_exit);

MODULE_LICENSE("GPL");

MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>");