sysfs接口函数到建立_DEVICE_ATTR

来源：互联网发布：随机数预测算法编辑：程序博客网时间：2024/06/05 19:38

转自：http://www.cnblogs.com/superlcc/archive/2012/08/08/2628290.html

可以参考的文档：http://www.wowotech.net/linux_kenrel/dm_sysfs.html

最近在弄Sensor驱动，看过一个某厂家的成品驱动，里面实现的全都是sysfs接口，hal层利用sysfs生成的接口，对Sensor进行操作。

说到sysfs接口，就不得不提到函数宏 DEVICE_ATTR

原型是#define DEVICE_ATTR(_name, _mode, _show, _store) \

structdevice_attribute dev_attr_##_name = __ATTR(_name, _mode, _show, _store)

函数宏DEVICE_ATTR内封装的是__ATTR(_name,_mode,_show,_stroe)方法，_show表示的是读方法，_stroe表示的是写方法，name是显示的文件名。

当然_ATTR不是独生子女，他还有一系列的姊妹__ATTR_RO宏只有读方法，__ATTR_NULL等等

如对设备的使用 DEVICE_ATTR ，对总线使用 BUS_ATTR ，对驱动使用 DRIVER_ATTR ，对类别 (class) 使用 CLASS_ATTR, 这四个高级的宏来自于<include/linux/device.h>

CLASS_ATTR 对应定义的是struct class_attribute, \\sysfs的转换以及操作函数(sysfs_ops)在kernel/driver/base/class.c

BUS_ATTR 对应定义的是struct bus_attribute \\sysfs的转换以及操作函数(sysfs_ops)在kernel/driver/base/bus.c

DEVICE_ATTR 宏声明有四个参数，分别是名称、权限位、读函数、写函数。其中读函数和写函数是读写功能函数的函数名。

如果你完成了DEVICE_ATTR函数宏的填充，下面就需要创建接口了

例如：

static DEVICE_ATTR(polling, S_IRUGO | S_IWUSR, show_polling, set_polling);
static struct attribute *dev_attrs[] = {
&dev_attr_polling.attr, //此处dev_attr_polling里的attr成员是一个struct attribute类型的变量
NULL,
};

当你想要实现的接口名字是polling的时候，需要实现结构体struct attribute *dev_attrs[]

其中成员变量的名字必须是&dev_attr_polling.attr

然后再封装

static struct attribute_group dev_attr_grp = {
.attrs = dev_attrs,
};

再利用sysfs_create_group(&pdev->dev.kobj, &dev_attr_grp);创建接口

通过以上简单的三个步骤，就可以在adb shell 终端查看到接口了。当我们将数据 echo 到接口中时，在上层实际上完成了一次 write 操作，对应到 kernel ，调用了驱动中的 “store”。同理，当我们cat 一个接口时则会调用 “show” 。到这里，只是简单的建立了 android 层到 kernel 的桥梁，真正实现对硬件操作的，还是在 "show" 和 "store" 中完成的。

内核有一个示例在 kernel/sample/kobject/kobject-example.c

######################################################################以下来个例子：/* * 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>#include <asm/gpio.h>#include <linux/delay.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;/* * The "foo" file where a static variable is read from and written to. */static struct msm_gpio qup_i2c_gpios_io[] = {     { GPIO_CFG(60, 0, GPIO_CFG_OUTPUT, GPIO_CFG_NO_PULL, GPIO_CFG_8MA),           "qup_scl" },     { GPIO_CFG(61, 0, GPIO_CFG_INPUT, GPIO_CFG_NO_PULL, GPIO_CFG_8MA),           "qup_sda" },     { GPIO_CFG(131, 0, GPIO_CFG_OUTPUT, GPIO_CFG_NO_PULL, GPIO_CFG_8MA),           "qup_scl" },     { GPIO_CFG(132, 0, GPIO_CFG_INPUT, GPIO_CFG_NO_PULL, GPIO_CFG_8MA),           "qup_sda" },};static struct msm_gpio qup_i2c_gpios_hw[] = {     { GPIO_CFG(60, 1, GPIO_CFG_INPUT, GPIO_CFG_NO_PULL, GPIO_CFG_8MA),           "qup_scl" },     { GPIO_CFG(61, 1, GPIO_CFG_INPUT, GPIO_CFG_NO_PULL, GPIO_CFG_8MA),           "qup_sda" },     { GPIO_CFG(131, 2, GPIO_CFG_INPUT, GPIO_CFG_NO_PULL, GPIO_CFG_8MA),           "qup_scl" },     { GPIO_CFG(132, 2, GPIO_CFG_INPUT, GPIO_CFG_NO_PULL, GPIO_CFG_8MA),           "qup_sda" },};static void gsbi_qup_i2c_gpio_config(int adap_id, int config_type){     int rc;     if (adap_id < 0 || adap_id > 1)           return;     /* Each adapter gets 2 lines from the table */     if (config_type)           rc = msm_gpios_enable(&qup_i2c_gpios_hw[adap_id*2], 2);     else           rc = msm_gpios_enable(&qup_i2c_gpios_io[adap_id*2], 2);     if (rc < 0)           pr_err("QUP GPIO request/enable failed: %d\n", rc);}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){     int sda,scl;     int i;     sscanf(buf, "%du", &foo);     printk("foo = %d.\n",foo);     foo = foo -1;     if  (foo < 0 || foo > 1)     {           printk("input foo error. foo=%d.\n",foo);           return 0;     }                 sda = GPIO_PIN((&qup_i2c_gpios_hw[foo*2+1])->gpio_cfg);      scl = GPIO_PIN((&qup_i2c_gpios_hw[foo*2])->gpio_cfg);           printk("sda = %d.\n",sda);     printk("scl = %d.\n",scl);          gsbi_qup_i2c_gpio_config(foo,0);     for(i=0;i<9;i++)     {           if(gpio_get_value(sda))           {                printk("sda of i2c%d is high when %d pulse is output on scl.\n",foo,i);                break;           }           gpio_set_value(scl,0);           udelay(5);           gpio_set_value(scl,1);           udelay(5);     }          gsbi_qup_i2c_gpio_config(foo,1);     printk("finish.\n");     return count;}static struct kobj_attribute foo_attribute =      __ATTR(i2c_unlock, 0666, foo_show, foo_store);/* * Create a group of attributes so that we can create and destroy them all * at once. */static struct attribute *attrs[] = {      &foo_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("i2c_recovery", 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("Wupeng");

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