Android 内核添加驱动

这是一个系列文章：

Android 内核添加驱动
测试freg驱动的功能内置C程程序
添加HAL层代码
添加JNI层
框架层添加硬件访问服务

该系列能对android的从下到上的各层有一个简单的设计，麻雀虽小，五脏俱全。enjoy now！

系列文章按照罗升阳大神的blog进行实践.向罗大神致敬!实现的是在从驱动层,HAL层,系统添加,JNI方法添加,AIDL方法添加,配置SELinux策略.由于android版本的差异,部分代码和配置需要修改,kernel和android源码版本不一样才能出错,这样才有试错,学习成长的机会.本文是参看<>以及罗大神的blog和其他网友的blog而来.本系列文章一共5篇，对应书中的第二章，做了对代码的适配工作以及自己的一点浅薄理解。

平台: Android N + kernel 3.18 + MTK

android/kernel-3.18/drivers/    ----freg        ----freg.c        ----freg.h        ----Kconfig        ----Makefile

freg.c

nclude #include #include #include #include #include #include #include #include #include "freg.h"static int freg_major = 0;static int freg_minor = 0;static struct class* freg_class = NULL;static struct fake_reg_dev* freg_dev = NULL;static int freg_open(struct inode* inode, struct file* filp);static int freg_release(struct inode* inode, struct file* filp);static ssize_t freg_read(struct file* filp, char __user *buf, size_t count, loff_t* f_pos);static ssize_t freg_write(struct file* filp, const char __user *buf, size_t count, loff_t* f_pos);static struct file_operations freg_fops = {    .owner = THIS_MODULE,    .open = freg_open,    .release = freg_release,    .read = freg_read,    .write = freg_write,};#define SEQ_printf(m, x...)     \    do {                \        if (m)          \            seq_printf(m, x);   \        else            \            pr_err(x);      \    } while (0)static int freg_proc_show(struct seq_file *m, void *v){    SEQ_printf(m, "%d\n", freg_dev->val);    return 0;}static int freg_proc_open(struct inode *inode, struct file *file){    return single_open(file, freg_proc_show, inode->i_private);}static ssize_t __freg_set_val(struct fake_reg_dev* dev, const char* buf, size_t count){    int val = 0;    val = simple_strtol(buf, NULL, 10);    if(down_interruptible(&(dev->sem))){        return -ERESTARTSYS;    }    dev->val = val;    up(&(dev->sem));    return count;}/*static ssize_t freg_proc_read(char* page, char** start, off_t off, int count, int* eof, void* data){    if(off >0 ){        *eof = 1;        return 0;    }    return __freg_get_val(freg_dev, page);}*/static ssize_t freg_proc_write(struct file *filp, const char *ubuf, size_t cnt, loff_t *data){    int err = 0;    char* page = NULL;    if(cnt > PAGE_SIZE){        printk(KERN_ALERT"The buff is too large: %lu.\n", cnt);        return -EFAULT;    }    page = (char*) __get_free_page(GFP_KERNEL);    if(!page){        printk(KERN_ALERT"Failed to alloc page.\n");        return -ENOMEM;    }    if(copy_from_user(page, ubuf, cnt)){        printk(KERN_ALERT"Failed to copy buff from user.\n");        err = -EFAULT;        goto out;    }    err = __freg_set_val(freg_dev, page, cnt);out:    free_page((unsigned long)page);    return err;}static const struct file_operations freg_proc_fops = {    .open = freg_proc_open,    .write = freg_proc_write,    .read = seq_read,    .llseek = seq_lseek,    .release = single_release,};static ssize_t freg_val_show(struct device* dev, struct device_attribute* attr, char* buf);static ssize_t freg_val_store(struct device* dev, struct device_attribute* attr, const char* buf, size_t count);static DEVICE_ATTR(val, S_IRUGO | S_IWUSR, freg_val_show, freg_val_store);static int freg_open(struct inode * inode, struct file * filp){    struct fake_reg_dev * dev;    dev = container_of(inode->i_cdev, struct fake_reg_dev, dev);    filp->private_data = dev;    return 0;}static int freg_release(struct inode* inode, struct file* filp){    return 0;}static ssize_t freg_read(struct file* filp, char __user *buf, size_t count, loff_t* f_pos){    ssize_t err = 0;    struct fake_reg_dev* dev = filp->private_data;    if(down_interruptible(&(dev->sem))){        return -ERESTARTSYS;    }    if(count < sizeof(dev->val)){        goto out;    }    if(copy_to_user(buf, &(dev->val), sizeof(dev->val))){        err = -EFAULT;        goto out;    }    err = sizeof(dev->val);out:    up(&(dev->sem));    return err;}static ssize_t freg_write(struct file * filp, const char __user * buf, size_t count, loff_t * f_pos){    struct fake_reg_dev* dev = filp->private_data;    ssize_t err = 0;    if(down_interruptible(&(dev->sem))){        return -ERESTARTSYS;    }    if(count != sizeof(dev->val)){        goto out;    }    if(copy_from_user(&(dev->val), buf, count)){        err = -EFAULT;        goto out;    }    err = sizeof(dev->val);out:    up(&(dev->sem));    return err;}static ssize_t __freg_get_val(struct fake_reg_dev* dev, char* buf){    int val = 0;    if(down_interruptible(&dev->sem)){        return -ERESTARTSYS;    }    val = dev->val;    up(&(dev->sem));    return snprintf(buf, PAGE_SIZE, "%d\n", val);}static ssize_t freg_val_show(struct device* dev, struct device_attribute* attr, char* buf){    struct fake_reg_dev* hdev = (struct fake_reg_dev*)dev_get_drvdata(dev);    return __freg_get_val(hdev, buf);}static ssize_t freg_val_store(struct device*dev, struct device_attribute* attr, const char* buf, size_t count){    struct fake_reg_dev* hdev = (struct fake_reg_dev*)dev_get_drvdata(dev);    return __freg_set_val(hdev, buf, count);}static void freg_create_proc(void){    proc_create(FREG_DEVICE_PROC_NAME, 0644, 0,  &freg_proc_fops);}static void freg_remove_proc(void){    remove_proc_entry(FREG_DEVICE_PROC_NAME, NULL);}static int __freg_setup_dev(struct fake_reg_dev* dev){    int err;    dev_t devno = MKDEV(freg_major, freg_minor);    memset(dev, 0, sizeof(struct fake_reg_dev));    cdev_init(&(dev->dev), &freg_fops);    dev->dev.owner = THIS_MODULE;    dev->dev.ops = &freg_fops;    err = cdev_add(&(dev->dev), devno, 1);    if(err){        return err;    }    //init_MUTEX(&(dev->sem));    sema_init(&(dev->sem), 1);    dev->val = 0;    return 0;}static int __init freg_init(void){    int err = -1;    dev_t dev = 0;    struct device* temp = NULL;    printk(KERN_ALERT"Initializing freg device.\n");    err = alloc_chrdev_region(&dev, 0, 1, FREG_DEVICE_NODE_NAME);    if(err < 0){        printk(KERN_ALERT"Failed to alloc char dev region.\n");        goto fail;    }    freg_major = MAJOR(dev);    freg_minor = MINOR(dev);    freg_dev = kmalloc(sizeof(struct fake_reg_dev), GFP_KERNEL);    if(!freg_dev){        err = -ENOMEM;        printk(KERN_ALERT"Failed to alloc freg device.\n");        goto unregister;    }    err = __freg_setup_dev(freg_dev);    if(err){        printk(KERN_ALERT"Failed to setup freg device: %d.\n", err);        goto cleanup;    }    freg_class = class_create(THIS_MODULE, FREG_DEVICE_CLASS_NAME);    if(IS_ERR(freg_class)){        err = PTR_ERR(freg_class);        printk(KERN_ALERT"Failed to create freg device class.\n");        goto destroy_cdev;    }    temp = device_create(freg_class, NULL, dev, NULL, "%s", FREG_DEVICE_FILE_NAME);    if(IS_ERR(temp)){        err = PTR_ERR(temp);        printk(KERN_ALERT"Failed to create freg device.\n");        goto destroy_class;    }    err = device_create_file(temp, &dev_attr_val);    if(err < 0){        printk(KERN_ALERT"Failed to create attribute val of freg device.\n");        goto destroy_device;    }    dev_set_drvdata(temp, freg_dev);    freg_create_proc();    printk(KERN_ALERT"Succedded to initialize freg device.\n");    return 0;destroy_device:    device_destroy(freg_class, dev);destroy_class:    class_destroy(freg_class);destroy_cdev:    cdev_del(&(freg_dev->dev));cleanup:    kfree(freg_dev);unregister:    unregister_chrdev_region(MKDEV(freg_major, freg_minor), 1);fail:    return err;}static void __exit freg_exit(void){    dev_t devno = MKDEV(freg_major, freg_minor);    printk(KERN_ALERT"Destory freg device.\n");    freg_remove_proc();    if(freg_class){        device_destroy(freg_class, MKDEV(freg_major, freg_minor));        class_destroy(freg_class);    }    if(freg_dev){        cdev_del(&(freg_dev->dev));        kfree(freg_dev);    }    unregister_chrdev_region(devno, 1);}MODULE_LICENSE("GPL");MODULE_DESCRIPTION("Fake Register Driver");module_init(freg_init);module_exit(freg_exit);

在kernel添加一个寄存器的驱动程序,具体代码的含义可以参考罗升阳的blog.

freg.h

#ifndef _FAKE_REG_H_#define _FAKE_REG_H_#include #include #define FREG_DEVICE_NODE_NAME  "freg"#define FREG_DEVICE_FILE_NAME  "freg"#define FREG_DEVICE_PROC_NAME  "freg"#define FREG_DEVICE_CLASS_NAME "freg"struct fake_reg_dev {    int val;    struct semaphore sem;    struct cdev dev;};#endif

Kconfig

config FREG    tristate "Fake Register Driver"    default y    help    This is the freg driver for android system.

这里设置为default y是让内核默认是编译的,若果设置成n就是默认不编译.按照罗大神的单编kernel没有成功,我有机器,没有使用模拟器

Makefile

obj-$(CONFIG_FREG) += freg.o

修改android/kernel-3.18/drivers下面的两个文件Kconfig和Makefile
在Kconfig文件

menu "Device Drivers"

下添加:

source "drivers/freg/Kconfig"

然后在android目录下进行make编译.如果在kernel-3.18目录下make过可能会导致整编不过,此时需要在把kernel-3.18下的目录下的.config文件删除.
编译成功进行刷机,adb shell进入机器,就可以看到里面有

proc/fregsys/class/fregdev/freg

dev查看需要root权限,可以先把机器root.dev目录下的访问需要权限,实现在添加HAL以及add到system_server时也会遇到SELinux的限制.这些在后续的相关文章有介绍.

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