在Ubuntu上为Android 10 系统编写Linux内核驱动程序

学习总纲：

Android10 硬件抽象层（HAL）概要介绍和学习计划

编写环境：

   - android 版本 - android-10.0.0_r41
   - 架构 - aosp_x86_64-eng
   - 内核分支：android-goldfish-4.14-gchips

参考资源

 罗升阳：https://blog.youkuaiyun.com/luoshengyang/article/details/6568411

目的

这篇博客的主要目的是补充罗升阳博客中我认为不够详细的地方和修改部分由于代码过时导致的编译错误。

补充不够详细的地方

1. 内核源码下载参考：https://blog.youkuaiyun.com/silently_frog/article/details/124063445

2. make menuconfig 命令的设置 (每次打开的新命令行窗口都需要设在)

     老罗博客中提到的 “Device Drivers” 和 “Enable loadable module support” 如下图红框部分：
   我门可以先只设置“Device Drivers” 如下图：
       注意，如果内核不支持动态加载模块，这里不能选择m，虽然我们在Kconfig文件中配置了HELLO选项为tristate。要支持动态加载模块选项，必须要在配置菜单中选择Enable loadable module support选项；在支持动态卸载模块选项，必须要在Enable loadable module support菜单项中，选择Module unloading选项。 如下图：
   

---

修改部分过时代码

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

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 <linux/slab.h>
#include <linux/seq_file.h>
#include <linux/sched.h>
#include <linux/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, size_t len, loff_t *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;
}


static int hello_proc_show(struct seq_file *m, void *v)
{
    seq_printf(m, "%d\n", hello_dev->val);
 
    return 0;
} 


static int hello_proc_open(struct inode *inode, struct file *filp)
{
    return single_open(filp, hello_proc_show, NULL);
}



static struct file_operations hello_proc_fops = {
    .owner = THIS_MODULE,
    .open = hello_proc_open,
    .write = hello_proc_write,
    .read = seq_read,
    .llseek = seq_lseek,
    .release = single_release
};
 
/*创建/proc/hello文件*/
static void hello_create_proc(void) {
   proc_create(HELLO_DEVICE_PROC_NAME, 0, NULL, &hello_proc_fops);
}
 
/*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*/
        sema_init(&(dev->sem), 1);
	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);