在/sys目录下建立一个文件，并且实现信息的读取和存储

下面通过在网络上截取的一个例子加以说明：

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 <[e-mail]>
 *  * 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 <[e-mail]>");

下面这个文件是本人修改的一个文件：

将目录修改为/sys/cpuInfo/下的cpuload、cpueffic、cpuoneeffic、cputwoeffic的大小为64的缓存空间。

这样就可以存储整形数据了。

#include <linux/kobject.h>
#include <linux/string.h>
#include <linux/sysfs.h>
#include <linux/module.h>
#include <linux/init.h>






/*************************************
 *在/sys/目录下建立cpuInfo目录，此目录中包含四个文件
 *
 *cpuload是一个静态变量，用于存储当前的cpu负载信息
 *
 *cpueffic是一个静态变量，用于存储cpu的平均使用率信息
 *
 *cpuoneeffic是一个静态变量，用于存储第一个cpu的使用率信息
 *
 *cputwoeffic是一个静态变量，用于存储第二个cpu使用率的信息
 *
 *************************************/




#define SIZE 64
static char  buffercpuload[SIZE];
static char  buffercpueffic[SIZE];
static char  buffercpuoneeffic[SIZE];
static char  buffercputwoeffic[SIZE];




static ssize_t cpuload_show(struct kobject *kobj, struct kobj_attribute *attr,char *buf)
{
return sprintf(buf, "%s \n", buffercpuload);
}


static ssize_t cpuload_store(struct kobject *kobj, struct kobj_attribute *attr,const char *buf, size_t count)
{
sscanf(buf, "%s", buffercpuload);
return count;
}


static struct kobj_attribute cpuload_attribute = __ATTR(cpuload, 0666, cpuload_show, cpuload_store);












static ssize_t cpueffic_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf)
{
return sprintf(buf, "%s \n", buffercpueffic);
}


static ssize_t cpueffic_store(struct kobject *kobj, struct kobj_attribute *attr, const char *buf, size_t count)
{
sscanf(buf, "%s", buffercpueffic);
return count;
}


static struct kobj_attribute cpueffic_attribute = __ATTR(cpueffic, 0666, cpueffic_show, cpueffic_store);












static ssize_t cputwoeffic_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf)
{
        return sprintf(buf, "%s \n", buffercputwoeffic);
}


static ssize_t cputwoeffic_store(struct kobject *kobj, struct kobj_attribute *attr, const char *buf, size_t count)
{
        sscanf(buf, "%s", buffercputwoeffic);
        return count;
}


static struct kobj_attribute cputwoeffic_attribute = __ATTR(cputwoeffic, 0666, cputwoeffic_show, cputwoeffic_store);










static ssize_t cpuoneeffic_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf)
{
        return sprintf(buf, "%s \n", buffercpuoneeffic);
}


static ssize_t cpuoneeffic_store(struct kobject *kobj, struct kobj_attribute *attr, const char *buf, size_t count)
{
        sscanf(buf, "%s", buffercpuoneeffic);
        return count;
}


static struct kobj_attribute cpuoneeffic_attribute = __ATTR(cpuoneeffic, 0666, cpuoneeffic_show, cpuoneeffic_store);




/************************
 *创建一个attributes组用来创建和销毁这些文件
 ********************** */






static struct attribute *attrs[] = {
&cpuload_attribute.attr,
&cpueffic_attribute.attr,
&cpuoneeffic_attribute.attr,
&cputwoeffic_attribute.attr,
NULL,
};


static struct attribute_group attr_group = {
.attrs = attrs,
};


static struct kobject *example_kobj;


static int __init example_init(void)
{
int retval;




/***************************
 ** 在/sys/目录下创建一个简单的kobject，名字是cpuInfo
 **************************/






example_kobj = kobject_create_and_add("cpuInfo", NULL);        中第一个参数是创建的目录的名称，第二个参数是创建的目录的位置，如果定义static struct kobject                                                                                                                                        *example_kobj;  并且把example_kobj置于NULL位置就会在/sys/kernel/目录下创建cpuInfo目录
if (!example_kobj)
return -ENOMEM;


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 <[e-mail]>");