在/sys目录下建立一个文件，并且实现信息的读取和存储

  此文件是在/sys/kernel/目录里面建立三个文件foo、baz、bar，每个文件都是静态的int型的缓存空间。

可以在这三个文件中读写一些整形的数据。

/*

 *  * 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 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)

{
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 destroy 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 __init 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 __exit 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>");

Makefile:

obj-m = systest.o

K_DIR = $(shell uname -r)

PWD = $(shell pwd)

all:
make -C /lib/modules/$(K_DIR)/build M=$(PWD) modules

clean:
make -C /lib/modules/$(K_DIR)/build M=$(PWD) clean

测试：

root@qinrenzhi-G31M-ES2C:/home/qinrenzhi/private/driver/sys# insmod systest.ko

root@qinrenzhi-G31M-ES2C:/home/qinrenzhi/private/driver/sys# cd /sys/kernel/kobject_example/

root@qinrenzhi-G31M-ES2C:/sys/kernel/kobject_example# ls

bar  baz  foo

root@qinrenzhi-G31M-ES2C:/sys/kernel/kobject_example# cat bar

1234

root@qinrenzhi-G31M-ES2C:/sys/kernel/kobject_example# echo 8888 > bar

root@qinrenzhi-G31M-ES2C:/sys/kernel/kobject_example# cat bar

8888