linux字符驱动设备.docx

Linux字符驱动设备的模板框架（2.4内核）/* leddrv.c - Create an input/output character device */#include #include #include #include /* for -EBUSY */#include /* for verify_area */#include /* for module_init */#include /* for get_user and put_user */#include #include drv.h#define BUF_LEN 4#define DEVICE_NAME char_dev/*驱动实现的功能函数*/static int device_open(struct inode *inode， struct file *file)static int device_release(struct inode *inode， struct file *file)static ssize_t device_read(struct file *file，char *buffer，size_t length， loff_t *offset) static ssize_t device_write(struct file *file，const char *buffer，size_t length，loff_t *offset)int device_ioctl(struct inode *inode，struct file *file，unsigned int ioctl_num， unsigned long ioctl_param) /*驱动实现的功能函数*/ /*模块加载、卸载、声明*/struct file_operations Fops = .read = device_read， .write = device_write，.open = device_open，.release = device_release，.ioctl= device_ioctl;/*这个文件结构体非常重要,联系内核和用户空间的桥梁*/* Initialize the module - Register the character device */static int _init led_module_init( void ) ret_val = register_chrdev(MAJOR_NUM， DEVICE_NAME， &Fops);/* Cleanup - unregister the appropriate file from /proc */static void _exit led_module_cleanup(void) ret = unregister_chrdev(MAJOR_NUM， DEVICE_NAME); ;module_init(led_module_init);module_exit(led_module_cleanup);MODULE_LICENSE(GPL);MODULE_AUTHOR(Cvtech Co.， Ltd );MODULE_DESCRIPTION(LED char driver);/*模块加载、卸载、声明*/重要函数的说明：1、 模块注册删除函数：模块注册register_chrdev(MAJOR_NUM， DEVICE_NAME， &Fops);功能：向内核注册一个字符驱动MAJOR_NUM 驱动主设备号。如果内核中已经相同的设备号，注册会失败。DEVICE_NAME设备名称模块删除unregister_chrdev( MAJOR_NUM， DEVICE_NAME ); 2、file_operationsstruct file_operations Fops = .read = device_read，/左边表示系统调用名称，右边表示编写的函数名.write = device_write，.open = device_open，.release = device_release，.ioctl= device_ioctl;file_operations结构体中的成员函数是字符驱动设备程序设计中的主体内容，这些函数实际会在应用程序进行Linux的open(),write(),close()等系统调用时最终被调用。file_operations的功能：file_operation就是把系统调用和驱动程序关联起来的关键数据结构。这个结构的每一个成员都对应着一个系统调用。读取file_operation中相应的函数指针，接着把控制权转交给函数，从而完成了Linux设备驱动程序的工作。 在系统内部，I/O设备的存取操作通过特定的入口点来进行，而这组特定的入口点恰恰是由设备驱动程序提供的。通常这组设备驱动程序接口是由结构file_operations结构体向系统说明的，它定义在include/linux/fs.h中。传统上, 一个 file_operation 结构或者其一个指针称为 fops( 或者它的一些变体). 结构中的每个成员必须指向驱动中的函数, 这些函数实现一个特别的操作, 或者对于不支持的操作留置为 NULL. 当指定为 NULL 指针时内核的确切的行为是每个函数不同的。file_operations的理解：内核内部通过file结构识别设备，通过file_operations数据结构提供文件系统的入口点函数，也就是访问设备驱动的函数。这个结构的每一个成员的名字都对应着一个系统调用。在用户进程利用系统调用对设备文件进行诸如read/write操作时，系统调用通过设备文件的主设备号找到相应的设备驱动程序，然后读取这个数据结构相应的函数指针，接着把控制权交给该函数，这是Linux设备驱动程序工作的基本原理。从某种意义上说，写驱动程序的任务之一就是完成file_operations中的函数指针。File_operations相关的函数说明：static int device_open(struct inode *inode， struct file *file)struct file代表一个打开的文件，在执行file_operation中的open操作时被创建，这里需要注意的是与用户空间inode指针的区别，一个在内核，而file指针在用户空间，由c库来定义。 struct inode被内核用来代表一个文件，注意和struct file的区别，struct inode一个是代表文件，struct file一个是代表打开的文件static ssize_t device_read(struct file *file，char *buffer，size_t length， loff_t *offset)struct file*file 为文件结构体指针char*buffer是读取文件的缓冲区size_t length为读取信息的长度loff_t*offset 是读取文件当前的偏移位置，这个值通常是用来判断文件是否越界注意：1、由于驱动工作在内核态，所以打印语句需要使用printk()而不是printf()2、 在驱动编写的device_open和device_write以及device_ioctl这几个个函数中会访问用户空间的内存，但是我们不能直接引用传递过来指针，这些传递过来的指针都是指向用户内存空间的，在驱动中需要使用get_usr()函数和put_usr()函数来实现内核内存空间和用户内存空间之间的数据复制。get_usr(int a,int *buffer)从用户空间写入字符到内核空间设备文件:从缓冲区写入到变量aput_usr(int a, int*buffer)从内核空间设备文件读入字符到用户空间实例：用户空间输入字符static ssize_t device_write(struct file *file， const char *buffer， size_t length， loff_t *offset) int value; int bytes_writes = 4; int* data = (int*)buffer;内核空间从用户空间复制字符 char str256; get_user(value， data); flags = value; sprintf(str， device_write %dn， flags); printk(str); /* Again， return the number of input characters used */ return bytes_writes;驱动实例/* leddrv.c - Create an input/output character device */#include #include #include #include /* for -EBUSY */#include /* for verify_area */#include /* for module_init */#include /* for get_user and put_user */#include #include drv.h#define BUF_LEN 4#define DEVICE_NAME char_devint device_ioctl(struct inode *，struct file *，unsigned int ，unsigned long ); /* This function is called whenever a process attempts * to open the device file */static int device_open(struct inode *inode， struct file *file) printk(Device Openn); /* We dont want to talk to two processes at the * same time */ if (Device_Open) return -EBUSY; Device_Open+; /标记打开的设备数 MOD_INC_USE_COUNT; /* Initialize the message */ Message_Ptr = Message; /消息队列 return 0;/* This function is called when a process closes the * device file. It doesnt have a return value because * it cannot fail. Regardless of what else happens， you * should always be able to close a device (in 2.0， a 2.2 * device file could be impossible to close). */static int device_release(struct inode *inode， struct file *file) printk(device_releasen); /* Were now ready for our next caller */ Device_Open -; /标记当前设备数 MOD_DEC_USE_COUNT; return 0;static int flags = 0xff;/* This function is called whenever a process which * has already opened the device file attempts to * read from it. */static ssize_t device_read( struct file *file， char *buffer， /* The buffer to fill with the data */ size_t length， /* The length of the buffer */ loff_t *offset) /* offset to the file */ /* Number of bytes actually written to the buffer */ int bytes_read = 4; int * data=(int *)buffer; char str256; sprintf(str， device_read %dn， flags); /flags读入str printk(str); put_user(flags， data); /* Read functions are supposed to return the number * of bytes actually inserted into the buffer */ return bytes_read;/* This function is called when somebody tries to * write into our device file. */ static ssize_t device_write(struct file *file， const char *buffer， size_t length， loff_t *offset) int value; int bytes_writes = 4; int* data = (int*)buffer; char str256; get_user(value， data); flags = value; sprintf(str， device_write %dn， flags); printk(str); /* Again， return the number of input characters used */ return bytes_writes;/* This function is called whenever a process tries to * do an ioctl on our device file. We get two extra * parameters (additional to the inode and file * structures， which all device functions get): the number * of the ioctl called and the parameter given to the * ioctl function. * * If the ioctl is write or read/write (meaning output * is returned to the calling process)， the ioctl call * returns the output of this function. */int device_ioctl( struct inode *inode， struct file *file， unsigned int ioctl_num，/* The number of the ioctl */ unsigned long ioctl_param) /* The parameter to it */ inttemp; int* data; int ioctl; char str256; printk(Device_ioctln); /* Switch according to the ioctl called */ switch (ioctl_num) case IOCTL_SET_MSG: /* Receive a pointer to a message (in user space) * and set that to be the devices message. */ /* Get the parameter given to ioctl by the process */ data = (int*) ioctl_param; get_user(temp， data); sprintf(str， Device_ioctl SET_MSG %dn， temp); printk(str); break; case IOCTL_GET_MSG: printk(Device_ioctl PUT_MSGn); break; return 0;/* Module Declarations * */* This structure will hold the functions to be called * when a process does something to the device we * created. Since a pointer to this structure is kept in * the devices table， it cant be local to * init_module. NULL is for unimplemented functions. */struct file_operations Fops = .read = device_read， .write = device_write，.open = device_open，.release = device_release，.ioctl= device_ioctl;/* Initialize the module - Register the character device */static int _init led_module_init( void ) int ret_val; /* Register the character device (atleast try) */ ret_val = register_chrdev(MAJOR_NUM， DEVICE_NAME， &Fops); /* Negative values signify an error */ if (ret_val 0) printk (%s failed with %dn， Sorry， registering the character device ， ret_val); return ret_val; printk (%s The major device number is %d.n， Registeration is a success， MAJOR_NUM); printk (If you want to talk to the device driver，n); printk (youll have to create a device file. n); printk (We suggest you use:n); printk (mknod %s c %d 0n， DEVICE_FILE_NAME，MAJOR_NUM); printk (The device file name is important， becausen); printk (the ioctl program assumes thats then); printk (file youll use.n); return 0;/* Cleanup - unregister the appropriate file from /proc */static void _exit led_module_cleanup(void) int ret; / release_region(LED_BASE， 12); /* Unregister the device */ ret = unregister_chrdev(MAJOR_NUM， DEVICE_NAME); /* If theres an error， report it */ if (ret 0) printk(Error in module_unregister_chrdev: %dn， ret);module_init(led_module_init);module_exit(led_module_cleanup);MODULE_LICENSE(GPL);MODULE_AUTHOR(Cvtech C