Linux内核分析（五）----字符设备驱动实现

                 1
                struct
                 file_operations {

                 2
                struct module *owner;/*拥有该结构的模块的指针，一般为THIS_MODULES*/ 3     loff_t (*llseek) (struct file *, loff_t, int); /*用来修改当前文件的读写指针*/ 4     ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);/*从设备读取数据*/ 5     ssize_t (*write) (struct file *, constchar __user *, size_t, loff_t *);/*向设备发送数据*/ 6     ssize_t (*aio_read) (struct kiocb *, conststruct iovec *, unsigned long, loff_t); /*初始化一个异步的读取操作*/ 7     ssize_t (*aio_write) (struct kiocb *, conststruct iovec *, unsigned long, loff_t); /*初始化一个异步的写入操作*/ 8int (*readdir) (struct file *, void *, filldir_t); /*只用于读取目录，对于设备文件该字段为NULL*/ 9     unsigned int (*poll) (struct file *, struct poll_table_struct *);/*轮询函数，判断目前是否可以进行非阻塞的读取或写入*/10long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long); /* 不用BLK的文件系统，将使用此函数代替ioctl*/11long (*compat_ioctl) (struct file *, unsigned int, unsigned long); /* 代替ioctl*/12int (*mmap) (struct file *, struct vm_area_struct *);/*用于请求将设备内存映射到进程地址空间*/13int (*open) (struct inode *, struct file *);/*打开*/14int (*flush) (struct file *, fl_owner_t id); /*在进程关闭它的设备文件描述符的拷贝时调用; 它应当执行(并且等待)设备的任何未完成的操作. */15int (*release) (struct inode *, struct file *);/*关闭*/16int (*fsync) (struct file *, int datasync); /*刷新待处理数据*/17int (*aio_fsync) (struct kiocb *, int datasync); /*异步fsync*/18int (*fasync) (int, struct file *, int); /*通知设备FASYNC标志发生变化*/19int (*lock) (struct file *, int, struct file_lock *);/* 实现文件加锁*/20     ssize_t (*sendpage) (struct file *, struct page *, int, size_t, loff_t *, int); /*通常为NULL*/21     unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long); /*在当前的进程地址空间找的一个未映射的内存段*/22int (*check_flags)(int); /*法允许模块检查传递给 fnctl(F_SETFL...) 调用的标志*/23int (*flock) (struct file *, int, struct file_lock *);/**/24     ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *, size_t, unsigned int); /*由VFS调用，将管道数据粘贴到文件*/25     ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *, size_t, unsigned int); /*由VFS调用，将文件数据粘贴到管道*/26int (*setlease)(struct file *, long, struct file_lock **);/**/27long (*fallocate)(struct file *file, int mode, loff_t offset,
28               loff_t len); /**/29 }; 

                  1 #include<linux/module.h>
  2 #include<linux/init.h>
  3 #include<linux/cdev.h>
  4 #include<linux/fs.h>
  5 #include<asm/uaccess.h>
  6  7#define MEM_SIZE 1024
  8  9 MODULE_LICENSE("GPL");
 10 11struct mem_dev{
 12struct cdev cdev;
 13int mem[MEM_SIZE];//全局内存4k 14    dev_t devno;
 15};
 16 17struct mem_dev my_dev;
 18 19/*打开设备*/ 20int mem_open(struct inode *inode, struct file *filp){
 21int num = MINOR(inode->i_rdev);/*获取次设备号*/ 22 23if(num == 0){/*判断为那个设备*/ 24         filp -> private_data = my_dev.mem;/*将设备结构体指针复制给文件私有数据指针*/ 25    }
 26return0;
 27}
 28/*文件关闭函数*/ 29int mem_release(struct inode *inode, struct file *filp){
 30return0;
 31}
 32 33static ssize_t mem_read(struct file *filp, char __user *buf, size_t size, loff_t *ppos){
 34int * pbase = filp -> private_data;/*获取数据地址*/ 35     unsigned long p = *ppos;/*读的偏移*/ 36     unsigned int count = size;/*读数据的大小*/ 37int ret = 0;
 38 39if(p >= MEM_SIZE)/*合法性判断*/ 40return0;
 41if(count > MEM_SIZE - p)/*读取大小修正*/ 42         count = MEM_SIZE - p;
 43 44if(copy_to_user(buf,pbase + p,size)){
 45        ret = - EFAULT;
 46     }else{
 47         *ppos += count;
 48         ret = count;
 49    }
 50 51return ret;
 52}
 53 54static ssize_t mem_write(struct file *filp, constchar __user *buf, size_t size, loff_t *ppos){
 55     unsigned long p = *ppos;
 56     unsigned int count = size;
 57int ret = 0;
 58int *pbase = filp -> private_data;
 59 60if(p >= MEM_SIZE)
 61return0;
 62if(count > MEM_SIZE - p)
 63         count = MEM_SIZE - p;
 64 65if(copy_from_user(pbase + p,buf,count)){
 66        ret = - EFAULT;
 67     }else{
 68         *ppos += count;
 69         ret = count;
 70    }
 71return ret;
 72}
 73 74/*seek文件定位函数*/ 75static loff_t mem_llseek(struct file *filp, loff_t offset, int whence){ 
 76 77    loff_t newpos;
 78 79switch(whence) {
 80case SEEK_SET:/*从文件头开始定位*/ 81             newpos = offset;
 82break;
 83case SEEK_CUR:/*从当前位置开始定位*/ 84             newpos = filp->f_pos + offset;
 85break;
 86case SEEK_END: 
 87             newpos = MEM_SIZE * sizeof(int)-1 + offset;/*从文件尾开始定位*/ 88break;
 89default:
 90return -EINVAL;
 91    }
 92 93if ((newpos<0) || (newpos>MEM_SIZE * sizeof(int)))/*检查文件指针移动后位置是否正确*/ 94return -EINVAL;
 95 96      filp->f_pos = newpos;
 97return newpos;
 98 99}
100101conststruct file_operations mem_ops = {
102     .llseek = mem_llseek,
103     .open = mem_open,
104     .read = mem_read,
105     .write = mem_write,
106     .release = mem_release,
107};
108109staticint memdev_init(void){
110int ret = -1;
111112/*动态分配设备号*/113     ret = alloc_chrdev_region(&my_dev.devno,0,1,"memdev");
114if (ret >= 0){
115         cdev_init(&my_dev.cdev,&mem_ops);/*初始化字符设备*/116         cdev_add(&my_dev.cdev,my_dev.devno,1);/*添加字符设备*/117    }
118119return ret;   
120}
121122staticvoid memdev_exit(void){
123     cdev_del(&my_dev.cdev);
124     unregister_chrdev_region(my_dev.devno,1);
125126}
127128module_init(memdev_init);
129 module_exit(memdev_exit);