/* * 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/slab.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 const 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 variable 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 destroy 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) {		kobject_put(&foo->kobj);		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 __init 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 __exit 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>");