kobject: add sample code for how to use ksets/ktypes/kobjects

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

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

/*

 * Sample kset and ktype 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 kset in sysfs called

 * /sys/kernel/kset-example

 * Then tree kobjects are created and assigned to this kset, "foo", "baz",

 * and "bar".  In those kobjects, attributes of the same name are also

 * created and if an integer is written to these files, it can be later

 * read out of it.

 */

/*

 * This is our "object" that we will create a few of and register them with

 * sysfs.

 */

struct foo_obj {

	struct kobject kobj;

	int foo;

	int baz;

	int bar;

};

#define to_foo_obj(x) container_of(x, struct foo_obj, kobj)

/* a custom attribute that works just for a struct foo_obj. */

struct foo_attribute {

	struct attribute attr;

	ssize_t (*show)(struct foo_obj *foo, struct foo_attribute *attr, char *buf);

	ssize_t (*store)(struct foo_obj *foo, struct foo_attribute *attr, const char *buf, size_t count);

};

#define to_foo_attr(x) container_of(x, struct foo_attribute, attr)

/*

 * The default show function that must be passed to sysfs.  This will be

 * called by sysfs for whenever a show function is called by the user on a

 * sysfs file associated with the kobjects we have registered.  We need to

 * transpose back from a "default" kobject to our custom struct foo_obj and

 * then call the show function for that specific object.

 */

static ssize_t foo_attr_show(struct kobject *kobj,

			     struct attribute *attr,

			     char *buf)

{

	struct foo_attribute *attribute;

	struct foo_obj *foo;

	attribute = to_foo_attr(attr);

	foo = to_foo_obj(kobj);

	if (!attribute->show)

		return -EIO;

	return attribute->show(foo, attribute, buf);

}

/*

 * Just like the default show function above, but this one is for when the

 * sysfs "store" is requested (when a value is written to a file.)

 */

static ssize_t foo_attr_store(struct kobject *kobj,

			      struct attribute *attr,

			      const char *buf, size_t len)

{

	struct foo_attribute *attribute;

	struct foo_obj *foo;

	attribute = to_foo_attr(attr);

	foo = to_foo_obj(kobj);

	if (!attribute->store)

		return -EIO;

	return attribute->store(foo, attribute, buf, len);

}

/* Our custom sysfs_ops that we will associate with our ktype later on */

static struct sysfs_ops foo_sysfs_ops = {

	.show = foo_attr_show,

	.store = foo_attr_store,

};

/*

 * The release function for our object.  This is REQUIRED by the kernel to

 * have.  We free the memory held in our object here.

 *

 * NEVER try to get away with just a "blank" release function to try to be

 * smarter than the kernel.  Turns out, no one ever is...

 */

static void foo_release(struct kobject *kobj)

{

	struct foo_obj *foo;

	foo = to_foo_obj(kobj);

	kfree(foo);

}

/*

 * The "foo" file where the .foo variable is read from and written to.

 */

static ssize_t foo_show(struct foo_obj *foo_obj, struct foo_attribute *attr,

			char *buf)

{

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

}

static ssize_t foo_store(struct foo_obj *foo_obj, struct foo_attribute *attr,

			 const char *buf, size_t count)

{

	sscanf(buf, "%du", &foo_obj->foo);

	return count;

}

static struct foo_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 foo_obj *foo_obj, struct foo_attribute *attr,

		      char *buf)

{

	int var;

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

		var = foo_obj->baz;

	else

		var = foo_obj->bar;

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

}

static ssize_t b_store(struct foo_obj *foo_obj, struct foo_attribute *attr,

		       const char *buf, size_t count)

{

	int var;

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

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

		foo_obj->baz = var;

	else

		foo_obj->bar = var;

	return count;

}

static struct foo_attribute baz_attribute =

	__ATTR(baz, 0666, b_show, b_store);

static struct foo_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 *foo_default_attrs[] = {

	&foo_attribute.attr,

	&baz_attribute.attr,

	&bar_attribute.attr,

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

};

/*

 * Our own ktype for our kobjects.  Here we specify our sysfs ops, the

 * release function, and the set of default attributes we want created

 * whenever a kobject of this type is registered with the kernel.

 */

static struct kobj_type foo_ktype = {

	.sysfs_ops = &foo_sysfs_ops,

	.release = foo_release,

	.default_attrs = foo_default_attrs,

};

static struct kset *example_kset;

static struct foo_obj *foo_obj;

static struct foo_obj *bar_obj;

static struct foo_obj *baz_obj;

static struct foo_obj *create_foo_obj(const char *name)

{

	struct foo_obj *foo;

	int retval;

	/* allocate the memory for the whole object */

	foo = kzalloc(sizeof(*foo), GFP_KERNEL);

	if (!foo)

		return NULL;

	/*

	 * As we have a kset for this kobject, we need to set it before calling

	 * the kobject core.

	 */

	foo->kobj.kset = example_kset;

	/*

	 * Initialize and add the kobject to the kernel.  All the default files

	 * will be created here.  As we have already specified a kset for this

	 * kobject, we don't have to set a parent for the kobject, the kobject

	 * will be placed beneath that kset automatically.

	 */

	retval = kobject_init_and_add(&foo->kobj, &foo_ktype, NULL, "%s", name);

	if (retval) {

		kfree(foo);

		return NULL;

	}

	/*

	 * We are always responsible for sending the uevent that the kobject

	 * was added to the system.

	 */

	kobject_uevent(&foo->kobj, KOBJ_ADD);

	return foo;

}

static void destroy_foo_obj(struct foo_obj *foo)

{

	kobject_put(&foo->kobj);

}

static int example_init(void)

{

	/*

	 * Create a kset with the name of "kset_example",

	 * located under /sys/kernel/

	 */

	example_kset = kset_create_and_add("kset_example", NULL, kernel_kobj);

	if (!example_kset)

		return -ENOMEM;

	/*

	 * Create three objects and register them with our kset

	 */

	foo_obj = create_foo_obj("foo");

	if (!foo_obj)

		goto foo_error;

	bar_obj = create_foo_obj("bar");

	if (!bar_obj)

		goto bar_error;

	baz_obj = create_foo_obj("baz");

	if (!baz_obj)

		goto baz_error;

	return 0;

baz_error:

	destroy_foo_obj(bar_obj);

bar_error:

	destroy_foo_obj(foo_obj);

foo_error:

	return -EINVAL;

}

static void example_exit(void)

{

	destroy_foo_obj(baz_obj);

	destroy_foo_obj(bar_obj);

	destroy_foo_obj(foo_obj);

	kset_unregister(example_kset);

}

module_init(example_init);

module_exit(example_exit);

MODULE_LICENSE("GPL");

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