Android : kernel中添加虚拟文件节点

　　Android 系统开发时有些数据需要同步到上层应用进行UI显示，如果是定制功能且数据量不大，可以考虑通过文件节点方式在应用和驱动之间进行通信。

　　以下介绍两种文件节点的添加方法：

一、/proc/节点：

#include <linux/uaccess.h>
#include <linux/proc_fs.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/delay.h>
#include <asm/uaccess.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <asm/irq.h>
#include <asm/io.h>

#define MSG_BUF_LEN     1024
static unsigned char msg_buf[MSG_BUF_LEN] = {0};
static unsigned int msg_len = 0;
static DECLARE_WAIT_QUEUE_HEAD(upgrade_percentage_waitq);

uint8_t  upgrade_percentage = 0;

//读接口
static ssize_t upgrade_percentage_read(struct file *file, char __user *user_buf,
             size_t count, loff_t *ppos)
{
    unsigned int ret = 0;
    
    // 如果 msg_len 为 0，则等待数据
    wait_event_interruptible(upgrade_percentage_waitq, msg_len);
    copy_to_user(user_buf, msg_buf, msg_len);
    ret = msg_len;
    msg_len = 0;
    
    printk("upgrade_percentage(r) : %d 
", upgrade_percentage);
    
    return ret;
}

//写接口
static ssize_t upgrade_percentage_write(struct file *file, const char __user *user_buf,
             size_t count, loff_t *ppos)
{
    if(copy_from_user(msg_buf, user_buf, count)) {
        return -EFAULT;
    }
    msg_len = count;
    wake_up_interruptible(&upgrade_percentage_waitq);
    return count;
}

const struct file_operations upgrade_percentage_operations = {
    .read =  upgrade_percentage_read,
    .write = upgrade_percentage_write,
};

static int nti2c_init(void)
{
    int ret;

    // -> "/proc/nt68411/upgrade_percentage"
    printk("proc_create upgrade_percentage ... 
");
    proc_mkdir("nt68411", NULL);
    proc_create("upgrade_percentage", S_IRUSR, NULL, &upgrade_percentage_operations);

　　return ret;
}

static void nti2c_exit(void)
{
    remove_proc_entry("nt68411/upgrade_percentage", NULL);
    printk("%s, ok! 
", __func__);
}

module_init(nti2c_init);
module_exit(nti2c_exit);

MODULE_AUTHOR("Sheldon");
MODULE_DESCRIPTION("driver for linux platform");
MODULE_LICENSE("GPL");

二、/sys/class/ 节点：

#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/mod_devicetable.h>
#include <linux/device.h>
#include <linux/platform_device.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/string.h>
#include <asm/uaccess.h>
#include <linux/delay.h>
#include <linux/of.h>
#include <linux/io.h>
#include <linux/gpio.h>
#include <linux/of_gpio.h>
#include <linux/vmalloc.h>
#include <linux/uaccess.h>
#include <linux/proc_fs.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <asm/irq.h>
#include <asm/io.h>


static struct class *driver_class = NULL;
static struct device *driver_dev = NULL;

static ssize_t driver_percentage_show(struct device *dev, struct device_attribute *attr, char *buf)
{
    printk("NT68411 upgrade_percentage : %d 
", upgrade_percentage);
    return sprintf(buf,"%u
",upgrade_percentage);
}

static ssize_t driver_percentage_store(struct device *dev, struct device_attribute *attr, const char *buf, size_t size)
{
    int value = simple_strtoul(buf, NULL, 0);
    printk("NT68411 driver_percentage_store : %d 
", value);
    return size;
}

static struct device_attribute dev_nt68411_upgrade_attr = {
    .attr = {
        .name = "percentage",
        .mode = 0666,
    },
    .show = driver_percentage_show,
    .store = driver_percentage_store,
};

static int nti2c_init(void)
{
    printk("%s, Enter 
", __func__);

　　 // --> /sys/class/nt68411/upgrade/percentage
    driver_class = class_create(THIS_MODULE, "nt68411");
     if (IS_ERR(driver_class)) {
        printk("nt68411 class_create fail
");
    }

    driver_dev = device_create(driver_class, NULL, 0, 0,"upgrade");
    if(NULL == driver_dev){
        printk("nt68411 device_create fail
");
    }
    device_create_file(driver_dev, &dev_nt68411_upgrade_attr);

    printk("%s, Exit 
", __func__);
    return 0;
}

static void nti2c_exit(void)
{
    device_remove_file(driver_dev, &dev_nt68411_upgrade_attr);
    device_unregister(driver_dev);
    if(driver_class!=NULL)
        class_destroy(driver_class);

    printk("%s, ok! 
", __func__);
}

module_init(nti2c_init);
module_exit(nti2c_exit);

MODULE_AUTHOR("Sheldon");
MODULE_DESCRIPTION("driver for linux platform");
MODULE_LICENSE("GPL");