在Ubuntu上为Android系统编写Linux内核驱动程序

1 source code

derek@u10:~/down/goldfish/drivers/hello$

derek@u10:~/down/goldfish/drivers/hello$ ls

hello.c hello.h Kconfig Makefile

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 <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);

Kconfig:

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

Makefile

obj-$(CONFIG_HELLO) += hello.o

2 修改一些makefile

修改arch/arm/Kconfig和drivers/kconfig两个文件，在menu "Device Drivers"和endmenu之间添加一行：

source "drivers/hello/Kconfig"

修改drivers/Makefile文件，添加一行：

obj-$(CONFIG_HELLO) += hello/

derek@u10:~/down/goldfish$ make menuconfig

找到"Device Drivers" => "First Android Drivers"选项，设置为y。

3 编译内核

export PATH=/home/derek/ics/ics-4.0.4/prebuilt/linux-x86/toolchain/arm-eabi-4.4.3/bin:$PATH
export ARCH=arm
export SUBARCH=arm
export CROSS_COMPILE=arm-eabi-

cd goldfish
make goldfish_armv7_defconfig  （Android4.0）
make

4 运行新内核，用adb检查

进入到dev目录，可以看到hello设备文件：
root@android:/ # cd dev
root@android:/dev # ls
进入到proc目录，可以看到hello文件：
root@android:/ # cd proc
root@android:/proc # ls
访问hello文件的值：
root@android:/proc # cat hello
0
root@android:/proc # echo '5' > hello
root@android:/proc # cat hello
5
进入到sys/class目录，可以看到hello目录：
root@android:/ # cd sys/class
root@android:/sys/class # ls
进入到hello目录，可以看到hello目录：
root@android:/sys/class # cd hello
root@android:/sys/class/hello # ls
进入到下一层hello目录，可以看到val文件：
root@android:/sys/class/hello # cd hello
root@android:/sys/class/hello/hello # ls
访问属性文件val的值：
root@android:/sys/class/hello/hello # cat val
5
root@android:/sys/class/hello/hello # echo '0'  > val
root@android:/sys/class/hello/hello # cat val
0