字符設備（順序讀寫，不帶緩衝）
塊設備（讀寫順序不固定，帶讀寫緩衝）常用sync命令（強行寫入硬件） 同步數據使數據真正寫進磁盤不然可能還在緩衝區
網絡設備：這傢伙破壞了linux一切皆文件規則。
字符設備框架：
硬件上有個字符設備，內核中就有個cdev結構與之對應
struct cdev {
struct kobject kobj;
struct module *owner;
const struct file_operations *ops;
struct list_head list;
dev_t dev;//設備號
unsigned int count;
};
每個cdev都有個設備號
設備號（32bits）=主設備號（高12bits）+次設備號（20bits）
主設備號：代表一個類型的設備
次設備號：用於區分設備的不同個體
主設備號的選取
->靜態分配
看現在內核中那些主設備號沒有被使用，選擇一個
查看 cat/proc/devoces已用的設備號
看內核源碼目錄下即Documentation\device.txt看看使用那些設備號
register_chedev_region(dev_t from,unsigned count,const char name)可以連續註冊多個字符設備號
from要註冊的起始設備號
count 連續註冊的設備個數
name名字
dev_t __u32 -> unsigned int 16位和32位移植兼容性才這麼設計的
#definrMINORBITS 20
MKDEV(ma（主設備號），mi（次設備號）) 他是個宏 其實源碼也就做了ma<<MINORBITS|mi)
unregister_chrdev_region(dev,nsigned count)卸載字符設備
->動態分配 但不是隨機分配
alloc_chrdev_region(dev_t *dev,unsigned baseminor,unsigned count,const char name)
註釋：
/**
* alloc_chrdev_region() - register a range of char device numbers
* @dev: output parameter for first assigned number
* @baseminor: first of the requested range of minor numbers
* @count: the number of minor numbers required
* @name: the name of the associated device or driver
*
* Allocates a range of char device numbers. The major number will be
* chosen dynamically, and returned (along with the first minor number)
* in @dev. Returns zero or a negative error code.
*/
獲取主設備號：
MAJOR(dev) dev>>MINORBITS
cdev的操作函數
cdev_init()//初始化cdev
void cdev_init(struct cdev *cdev, const struct file_operations *fops)
{
memset(cdev, 0, sizeof *cdev);
INIT_LIST_HEAD(&cdev->list);
kobject_init(&cdev->kobj, &ktype_cdev_default);
cdev->ops = fops;
}
cdev_add()//向內核註冊cdev
int cdev_add(struct cdev *p, dev_t dev, unsigned count)
{
p->dev = dev;
p->count = count;
return kobj_map(cdev_map, dev, count, NULL, exact_match, exact_lock, p);
}
struct file_operations {
struct module *owner;
loff_t (*llseek) (struct file *, loff_t, int);
ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
ssize_t (*aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
int (*readdir) (struct file *, void *, filldir_t);
unsigned int (*poll) (struct file *, struct poll_table_struct *);
.....
};
_exit 要逆序消除 _init產生的影響
cdev_del()
unregister_chrdev_region(dev,nsigned count)
手工創建設備節點文件
mknod /dev/xxx c 248 0
主 次
arm-none-linux-gnueabi-gcc -o
簡單小示例：
#include <linux/init.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/cdev.h>
MODULE_LICENSE("Dua BSD/GPL");
MODULE_AUTHOR("Songmao");
MODULE_DESCRIPTION("cdev tast");
#define TCDEV_MAJOR 0
#define TCDEV_MINOR 0
#define TCDEV_NUM 1
#define TCDEV_NAME "mytcdev"
static int tcdev_major =TCDEV_MAJOR,tcdev_minor=TCDEV_MINOR;
module_param(tcdev_major,int,S_IRWXU);
module_param(tcdev_minor,int,S_IRWXU);
static int tcdev_open(struct inode * node,struct file * filep)
{
printk(KERN_INFO "tcdev open\n");
return 0;
}
static ssize_t tcdev_read(struct file *file, char __user *buf, size_t count, loff_t *fops)
{
printk(KERN_INFO "tcdev read\n");
return 0;
}
static ssize_t tcdev_write (struct file *file, char __user *buf, size_t count, loff_t *fops)
{
printk(KERN_INFO "tcdev write\n");
return 0;
}
static int tcdev_release(struct inode * node,struct file * filep)
{
printk(KERN_INFO "tcdev write\n");
return 0;
}
static struct file_operations tcdev_fops = {
.owner=THIS_MODULE,
.open=tcdev_open,
.read=tcdev_read,
.write=tcdev_write,
.release=tcdev_release,
};
static struct cdev tcdev;
static int __init tcdev_init(void)
{
int ret =-EFAULT;
dev_t tcdev_t;
tcdev_t=MKDEV(tcdev_major,tcdev_minor);
printk(KERN_INFO "tcdev start ...\n");
if(tcdev_major==0){
ret= alloc_chrdev_region(&tcdev_t,tcdev_minor,TCDEV_NUM,TCDEV_NAME);
if(ret<0){
printk(KERN_ERR"tcdev cdev num apply is fail\n");
goto tcdev_cdev_fail;
}
}
else{
ret=register_chrdev_region(tcdev_t,TCDEV_NUM,TCDEV_NAME);
if(ret<0){
printk(KERN_ERR "tcdev cdev num apply is fail\n");
goto tcdev_cdev_fail;
}
}
printk(KERN_INFO "tcdev cdev num apply is success,dev_t is %d\n",tcdev_t);
memset(&tcdev,0,sizeof(struct cdev));
cdev_init(&tcdev,&tcdev_fops);
ret=cdev_add(&tcdev,tcdev_t,TCDEV_NUM);
if(ret<0){
printk(KERN_ERR"tcdev cdev cdev_add is fail\n");
goto tcdev_cdev_add_fail;
}
printk(KERN_INFO"tcdev cdev_add apply is success\n");
return 0;
tcdev_cdev_add_fail:
unregister_chrdev_region(&tcdev,TCDEV_NUM);
tcdev_cdev_fail:
return 0;
}
static void __exit tcdev_exit (void)
{
printk(KERN_INFO "tcdev stop ...\n");
cdev_del(&tcdev);
printk(KERN_INFO"tcdev del success\n");
unregister_chrdev_region(&tcdev,TCDEV_NUM);
printk(KERN_INFO "tcdev dev_num del success\n");
return 0;
}
module_init(tcdev_init);
module_exit(tcdev_exit);
Makefile
#!/bin/bash
obj-m += testcdev.o
KDIR := /home/topeet/android4.0/iTop4412_Kernel_3.0
#當前目錄變量
PWD ?= $(shell pwd)
#make命名默認尋找第一個目標
#make -C就是指調用執行的路徑
#$(KDIR)Linux源碼目錄，作者這裏指的是/home/topeet/android4.0/iTop4412_Kernel_3.0
#$(PWD)當前目錄變量
#modules要執行的操作
all:
make -C $(KDIR) M=$(PWD) modules
#make clean執行的操作是刪除後綴爲o的文件
clean:
rm -rf *.mod.c *.o *.order *.ko *.mod.o *.symvers
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>
char buf[20];
/*argv[1] is cmd , argv[2] is io_arg*/
int main(int argc , char **argv){
int fd;
char *lednode = "/dev/tcdev";
if((fd = open(lednode,O_RDWR|O_NDELAY))<0){
printf("APP open %s failed!\n",lednode);
}
else{
printf("APP open %s success!\n",lednode);
read(fd,buf,20);
return 0;
}