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

This is a simple kobject module, showing how to use kobj_attributes in
basic and more complex ways.

Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

samples/Kconfig

@@ -13,4 +13,14 @@ config SAMPLE_MARKERS
 	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
+

samples/Makefile

 # Makefile for Linux samples code
 
-obj-$(CONFIG_SAMPLES)	+= markers/
+obj-$(CONFIG_SAMPLES)	+= markers/ kobject/

samples/kobject/Makefile

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

samples/kobject/kobject-example.c

+/*
+ * 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>");