编写一个随内核加载的简单驱动

    接上篇内核编译继续编一个简单的随内核加载的驱动。
1、进入内核代码所在路径
2、cd goldfish/drivers
3、mkdir hello
4、cd hello
5、创建hello.h

#ifndef _HELLO_ANDROID_H_
#define _HELLO_ANDROID_H_

#include <linux/cdev.h>
#include <linux/semaphore.h>

#define HELLO_DEVICE_NODE_NAME  "hello"
#define HELLO_DEVICE_FILE_NAME  "hello"
#define HELLO_DEVICE_PROC_NAME  "hello"
#define HELLO_DEVICE_CLASS_NAME "hello"

struct hello_android_dev {
    int val;
    struct semaphore sem;
    struct cdev dev;
};

#endif

6、创建hello.c

#include <linux/init.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/fs.h>
#include <linux/proc_fs.h>
#include <linux/device.h>
#include <asm/uaccess.h>

#include "hello.h"

/*主设备和从设备号变量*/
static int hello_major = 0;
static int hello_minor = 0;

/*设备类别和设备变量*/
static struct class* hello_class = NULL;
static struct hello_android_dev* hello_dev = NULL;

/*传统的设备文件操作方法*/
static int hello_open(struct inode* inode, struct file* filp);
static int hello_release(struct inode* inode, struct file* filp);
static ssize_t hello_read(struct file* filp, char __user *buf, size_t count, loff_t* f_pos);
static ssize_t hello_write(struct file* filp, const char __user *buf, size_t count, loff_t* f_pos);

/*设备文件操作方法表*/
static struct file_operations hello_fops = {
    .owner = THIS_MODULE,
    .open = hello_open,
    .release = hello_release,
    .read = hello_read,
    .write = hello_write,
};

/*访问设置属性方法*/
static ssize_t hello_val_show(struct device* dev, struct device_attribute* attr,  char* buf);
static ssize_t hello_val_store(struct device* dev, struct device_attribute* attr, const char* buf, size_t count);

/*定义设备属性*/
static DEVICE_ATTR(val, S_IRUGO | S_IWUSR, hello_val_show, hello_val_store);

/*打开设备方法*/
static int hello_open(struct inode* inode, struct file* filp) {
    struct hello_android_dev* dev;

    /*将自定义设备结构体保存在文件指针的私有数据域中，以便访问设备时拿来用*/
    dev = container_of(inode->i_cdev, struct hello_android_dev, dev);
    filp->private_data = dev;

    return 0;
}

/*设备文件释放时调用，空实现*/
static int hello_release(struct inode* inode, struct file* filp) {
    return 0;
}

/*读取设备的寄存器val的值*/
static ssize_t hello_read(struct file* filp, char __user *buf, size_t count, loff_t* f_pos) {
    ssize_t err = 0;
    struct hello_android_dev* dev = filp->private_data;

    /*同步访问*/
    if(down_interruptible(&(dev->sem))) {
        return -ERESTARTSYS;
    }

    if(count < sizeof(dev->val)) {
        goto out;
    }

    /*将寄存器val的值拷贝到用户提供的缓冲区*/
    if(copy_to_user(buf, &(dev->val), sizeof(dev->val))) {
        err = -EFAULT;
        goto out;
    }

    err = sizeof(dev->val);

out:
    up(&(dev->sem));
    return err;
}

/*写设备的寄存器值val*/
static ssize_t hello_write(struct file* filp, const char __user *buf, size_t count, loff_t* f_pos) {
    struct hello_android_dev* dev = filp->private_data;
    ssize_t err = 0;

    /*同步访问*/
    if(down_interruptible(&(dev->sem))) {
        return -ERESTARTSYS;
    }

    if(count != sizeof(dev->val)) {
        goto out;
    }

    /*将用户提供的缓冲区的值写到设备寄存器去*/
    if(copy_from_user(&(dev->val), buf, count)) {
        err = -EFAULT;
        goto out;
    }

    err = sizeof(dev->val);

out:
    up(&(dev->sem));
    return err;
}

/*读取寄存器val的值到缓冲区buf中，内部使用*/
static ssize_t __hello_get_val(struct hello_android_dev* dev, char* buf) {
    int val = 0;

    /*同步访问*/
    if(down_interruptible(&(dev->sem))) {
        return -ERESTARTSYS;
    }

    val = dev->val;
    up(&(dev->sem));

    return snprintf(buf, PAGE_SIZE, "%d\n", val);
}

/*把缓冲区buf的值写到设备寄存器val中去，内部使用*/
static ssize_t __hello_set_val(struct hello_android_dev* dev, const char* buf, size_t count) {
    int val = 0;

    /*将字符串转换成数字*/
    val = simple_strtol(buf, NULL, 10);

    /*同步访问*/
    if(down_interruptible(&(dev->sem))) {
        return -ERESTARTSYS;
    }

    dev->val = val;
    up(&(dev->sem));

    return count;
}

/*读取设备属性val*/
static ssize_t hello_val_show(struct device* dev, struct device_attribute* attr, char* buf) {
    struct hello_android_dev* hdev = (struct hello_android_dev*)dev_get_drvdata(dev);

    return __hello_get_val(hdev, buf);
}

/*写设备属性val*/
static ssize_t hello_val_store(struct device* dev, struct device_attribute* attr, const char* buf, size_t count) {
    struct hello_android_dev* hdev = (struct hello_android_dev*)dev_get_drvdata(dev);

    return __hello_set_val(hdev, buf, count);
}

/*读取设备寄存器val的值，保存在page缓冲区中*/
static ssize_t hello_proc_read(char* page, char** start, off_t off, int count, int* eof, void* data) {
    if(off > 0) {
        *eof = 1;
        return 0;
    }

    return __hello_get_val(hello_dev, page);
}

/*把缓冲区的值buff保存到设备寄存器val中去*/
static ssize_t hello_proc_write(struct file* filp, const char __user *buff, unsigned long len, void* data) {
    int err = 0;
    char* page = NULL;

    if(len > PAGE_SIZE) {
        printk(KERN_ALERT"The buff is too large: %lu.\n", len);
        return -EFAULT;
    }

    page = (char*)__get_free_page(GFP_KERNEL);
    if(!page) {
        printk(KERN_ALERT"Failed to alloc page.\n");
        return -ENOMEM;
    }

    /*先把用户提供的缓冲区值拷贝到内核缓冲区中去*/
    if(copy_from_user(page, buff, len)) {
        printk(KERN_ALERT"Failed to copy buff from user.\n");
        err = -EFAULT;
        goto out;
    }

    err = __hello_set_val(hello_dev, page, len);

out:
    free_page((unsigned long)page);
    return err;
}

/*创建/proc/hello文件*/
static void hello_create_proc(void) {
    struct proc_dir_entry* entry;

    entry = create_proc_entry(HELLO_DEVICE_PROC_NAME, 0, NULL);
    if(entry) {
        entry->owner = THIS_MODULE;
        entry->read_proc = hello_proc_read;
        entry->write_proc = hello_proc_write;
    }
}

/*删除/proc/hello文件*/
static void hello_remove_proc(void) {
    remove_proc_entry(HELLO_DEVICE_PROC_NAME, NULL);
}

/*初始化设备*/
static int  __hello_setup_dev(struct hello_android_dev* dev) {
    int err;
    dev_t devno = MKDEV(hello_major, hello_minor);

    memset(dev, 0, sizeof(struct hello_android_dev));

    cdev_init(&(dev->dev), &hello_fops);
    dev->dev.owner = THIS_MODULE;
    dev->dev.ops = &hello_fops;

    /*注册字符设备*/
    err = cdev_add(&(dev->dev),devno, 1);
    if(err) {
        return err;
    }

    /*初始化信号量和寄存器val的值*/
    init_MUTEX(&(dev->sem));
    dev->val = 0;

    return 0;
}

/*模块加载方法*/
static int __init hello_init(void){
    int err = -1;
    dev_t dev = 0;
    struct device* temp = NULL;

    printk(KERN_ALERT"Initializing hello device.\n");

    /*动态分配主设备和从设备号*/
    err = alloc_chrdev_region(&dev, 0, 1, HELLO_DEVICE_NODE_NAME);
    if(err < 0) {
        printk(KERN_ALERT"Failed to alloc char dev region.\n");
        goto fail;
    }

    hello_major = MAJOR(dev);
    hello_minor = MINOR(dev);

    /*分配helo设备结构体变量*/
    hello_dev = kmalloc(sizeof(struct hello_android_dev), GFP_KERNEL);
    if(!hello_dev) {
        err = -ENOMEM;
        printk(KERN_ALERT"Failed to alloc hello_dev.\n");
        goto unregister;
    }

    /*初始化设备*/
    err = __hello_setup_dev(hello_dev);
    if(err) {
        printk(KERN_ALERT"Failed to setup dev: %d.\n", err);
        goto cleanup;
    }

    /*在/sys/class/目录下创建设备类别目录hello*/
    hello_class = class_create(THIS_MODULE, HELLO_DEVICE_CLASS_NAME);
    if(IS_ERR(hello_class)) {
        err = PTR_ERR(hello_class);
        printk(KERN_ALERT"Failed to create hello class.\n");
        goto destroy_cdev;
    }

    /*在/dev/目录和/sys/class/hello目录下分别创建设备文件hello*/
    temp = device_create(hello_class, NULL, dev, "%s", HELLO_DEVICE_FILE_NAME);
    if(IS_ERR(temp)) {
        err = PTR_ERR(temp);
        printk(KERN_ALERT"Failed to create hello device.");
        goto destroy_class;
    }

    /*在/sys/class/hello/hello目录下创建属性文件val*/
    err = device_create_file(temp, &dev_attr_val);
    if(err < 0) {
        printk(KERN_ALERT"Failed to create attribute val.");
        goto destroy_device;
    }

    dev_set_drvdata(temp, hello_dev);

    /*创建/proc/hello文件*/
    hello_create_proc();

    printk(KERN_ALERT"Succedded to initialize hello device.\n");
    return 0;

destroy_device:
    device_destroy(hello_class, dev);

destroy_class:
    class_destroy(hello_class);

destroy_cdev:
    cdev_del(&(hello_dev->dev));

cleanup:
    kfree(hello_dev);

unregister:
    unregister_chrdev_region(MKDEV(hello_major, hello_minor), 1);

fail:
    return err;
}

/*模块卸载方法*/
static void __exit hello_exit(void) {
    dev_t devno = MKDEV(hello_major, hello_minor);

    printk(KERN_ALERT"Destroy hello device.\n");

    /*删除/proc/hello文件*/
    hello_remove_proc();

    /*销毁设备类别和设备*/
    if(hello_class) {
        device_destroy(hello_class, MKDEV(hello_major, hello_minor));
        class_destroy(hello_class);
    }

    /*删除字符设备和释放设备内存*/
    if(hello_dev) {
        cdev_del(&(hello_dev->dev));
        kfree(hello_dev);
    }

    /*释放设备号*/
    unregister_chrdev_region(devno, 1);
}

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("First Android Driver");

module_init(hello_init);
module_exit(hello_exit);

7、创建Kconfig

config HELLO
              tristate "First Android Driver"
              default n
              help
              This is the first android driver.

8、创建Makefile

obj-$(CONFIG_HELLO) += hello.o

9、进入内核源代码的goldfish/arch/arm路径
10、在Kconfig文件中的menu "Device Drivers"和endmenu之间添加：
source "drivers/hello/Kconfig"
11、进入内核源代码的goldfish/drivers路径
12、在Kconfig文件中的menu "Device Drivers"和endmenu之间添加：
source "drivers/hello/Kconfig"
13、在Makefile文件中添加：
obj-$(CONFIG_HELLO) += hello/
14、进入goldfish路径
15、make menuconfig
"Device Drivers" => "First Android Drivers"选项选中
16、make
17、emulator -kernel 内核源代码路径/goldfish/arch/arm/boot/zImage -avd a_avd&
18、adb shell
19、察看驱动是否随内核加载
ls /dev
ls /proc
20、验证驱动是否可用

cd proc
cat hello
echo '5' > hello
cat hello
cd /sys/class
cd hello
cd hello
cat val
echo '0'  > val
cat val