在/sys下面创建属性文件

以前一直有一个疑问：驱动到底在哪里创建文件节点才有意义，才能满足应用层的需求。后来一直得不到解答，慢慢的就不干觉得有困惑。因为android的开发

，从原厂拿到bsp大多数驱动都已经做好了，功能健全，通过HAL提供本地方法。其实事实还有其他的途径提供驱动接口，比如字符设备，创建一个文件节点，

然后JNI层包装一下节点的操作函数，向java层提供public class；输入设备，上报按键，触摸屏等输入设备的值；在/sys下创建属性文件，对设备/驱动/总线

提供直接操作的方法，在java层直接可以调用shell语句来操作文件，完成访问硬件驱动资源的任务。。。

正所谓条条大道通罗马！^_^

下面是重点，在驱动中使用/sys文件系统操作方法创建属性文件的过程如下面的两个例子，标红的为重点过程。

1，创建一个属性文件

#include <linux/module.h>#include <linux/kernel.h>#include <linux/init.h>#include <linux/platform_device.h>#include <linux/fb.h>#include <linux/backlight.h>#include <linux/err.h>#include <linux/slab.h>#include <linux/gpio.h>#include <mach/platform.h>#include <linux/delay.h>#define GPIO_OUTA ((PAD_GPIO_B + 28) | PAD_FUNC_ALT0)#define GPIO_OUTB ((PAD_GPIO_D + 28) | PAD_FUNC_ALT0)unsigned long isLOCK =0;static ssize_t lock_show(struct device* cd,struct device_attribute *attr, char* buf){ssize_t ret = 0;sprintf(buf, "lock_show %d\n",isLOCK);ret = strlen(buf) + 1;return ret;}/*echo 1 >/sys/devices/platform/rk29-keypad/doorlock open**echo 0 >/sys/devices/platform/rk29-keypad/doorlock close**echo 2 >/sys/devices/platform/rk29-keypad/doorlock stop*/static ssize_t lock_store(struct device* cd, struct device_attribute *attr,const char* buf, size_t len){unsigned long on_off = simple_strtoul(buf, NULL, 10);isLOCK = on_off;printk("%s: %d\n",__func__, isLOCK);if(isLOCK == 1){gpio_direction_output(GPIO_OUTA, 1);gpio_direction_output(GPIO_OUTB, 0);mdelay(150);}else if(isLOCK == 0){gpio_direction_output(GPIO_OUTA, 0);gpio_direction_output(GPIO_OUTB, 1);mdelay(150);}else{gpio_direction_output(GPIO_OUTA, 1);gpio_direction_output(GPIO_OUTB, 1);}gpio_direction_output(GPIO_OUTA, 1);gpio_direction_output(GPIO_OUTB, 1);return len;}static DEVICE_ATTR(doorLock, S_IRUGO | S_IWUSR, lock_show, lock_store);/**GPIO_OUTA GPIO_OUTB STATE* 0 0 wait* 1 0 + run* 0 1 - run* 1 1 stop */static int lock_gpio_probe(struct platform_device *pdev){int err=0;printk("=====lock_gpio_probe start=======\n");gpio_request(GPIO_OUTA,"gpio_outa");gpio_direction_output(GPIO_OUTA, 0);gpio_request(GPIO_OUTB,"gpio_outb");gpio_direction_output(GPIO_OUTB, 0);printk("=====lock_gpio_probe over=======\n");if ((err = device_create_file(&pdev->dev, &dev_attr_doorLock)))goto err_out;return 0 ;err_out:return 1;}static int lock_gpio_remove(struct platform_device *pdev){return 0 ;}static struct platform_driver lock_gpio_driver = {.driver = {.name = "rk29-keypad",//lock-gpio.owner = THIS_MODULE,},.probe = lock_gpio_probe,.remove = lock_gpio_remove,};module_platform_driver(lock_gpio_driver);MODULE_DESCRIPTION("gpio based lock Driver");MODULE_LICENSE("GPL");MODULE_AUTHOR("Eliot_shao");

dev_attr_doorLock就是DEVICE_ATTR宏创建的变量！lock_show&lock_store是属性文件的读写方法，实现方法见历程。

2,创建一组属性文件

#include <linux/fs.h>#include <asm/uaccess.h>#include <linux/pci.h>#include <linux/input.h>#include <linux/platform_device.h>struct input_dev *vms_input_dev;        /* Representation of an input device */static struct platform_device *vms_dev; /* Device structure */                                        /* Sysfs method to input simulated                                           coordinates to the virtual                                           mouse driver */static ssize_twrite_vms(struct device *dev,          struct device_attribute *attr,          const char *buffer, size_t count){  int x,y;  sscanf(buffer, "%d%d", &x, &y);                                        /* Report relative coordinates via the                                           event interface */  input_report_rel(vms_input_dev, REL_X, x);  input_report_rel(vms_input_dev, REL_Y, y);  input_sync(vms_input_dev);  return count;}/* Attach the sysfs write method */DEVICE_ATTR(coordinates, 0644, NULL, write_vms);/* Attribute Descriptor */static struct attribute *vms_attrs[] = {  &dev_attr_coordinates.attr,  NULL};/* Attribute group */static struct attribute_group vms_attr_group = {  .attrs = vms_attrs,};/* Driver Initialization */int __initvms_init(void){  /* Register a platform device */  vms_dev = platform_device_register_simple("vms", -1, NULL, 0);  if (IS_ERR(vms_dev)) {    PTR_ERR(vms_dev);    printk("vms_init: error\n");  }  /* Create a sysfs node to read simulated coordinates */  sysfs_create_group(&vms_dev->dev.kobj, &vms_attr_group);  /* Allocate an input device data structure */  vms_input_dev = input_allocate_device();  if (!vms_input_dev) {    printk("Bad input_alloc_device()\n");  }  /* Announce that the virtual mouse will generate     relative coordinates */  set_bit(EV_REL, vms_input_dev->evbit);  set_bit(REL_X, vms_input_dev->relbit);  set_bit(REL_Y, vms_input_dev->relbit);  /* Register with the input subsystem */  input_register_device(vms_input_dev);  printk("Virtual Mouse Driver Initialized.\n");  return 0;}/* Driver Exit */voidvms_cleanup(void){  /* Unregister from the input subsystem */  input_unregister_device(vms_input_dev);  /* Cleanup sysfs node */  sysfs_remove_group(&vms_dev->dev.kobj, &vms_attr_group);  /* Unregister driver */  platform_device_unregister(vms_dev);  return;}module_init(vms_init);module_exit(vms_cleanup);</span>

属性文件的操作方法很简单，如

echo 1  >/sys/devices/platform/lock-gpio/doorlock 

cat /sys/devices/platform/lock-gpio/doorlock