1.前言
Linux内核就是由各种驱动组成的
Linux操作系统将所有的设备都看成文件,以操作文件的方式访问设备。
应用程序不能直接操作硬件,而是通过使用统一的接口函数调用硬件驱动程序。
2.字符设备驱动程序中重要的数据结构和函数
重要的数据结构和函数
可以在glibc的fcntl.h、unistd.h、sys/ioctl.h等文件中看到(应用程序中使用的接口)
对于上述每个系统调用,驱动程序中国都有一个与之对应的函数对于字符设备驱动程序,这些函数集合在一个file_operations类型的数据结构中。file_operations结构在内核的include/linux/fs.h中定义
file_operations
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 *);
long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
int (*mmap) (struct file *, struct vm_area_struct *);
int (*open) (struct inode *, struct file *);
int (*flush) (struct file *, fl_owner_t id);
int (*release) (struct inode *, struct file *);
int (*fsync) (struct file *, loff_t, loff_t, int datasync);
int (*aio_fsync) (struct kiocb *, int datasync);
int (*fasync) (int, struct file *, int);
int (*lock) (struct file *, int, struct file_lock *);
ssize_t (*sendpage) (struct file *, struct page *, int, size_t, loff_t *, int);
unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
int (*check_flags)(int);
int (*flock) (struct file *, int, struct file_lock *);
ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *, size_t, unsigned int);
ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *, size_t, unsigned int);
int (*setlease)(struct file *, long, struct file_lock **);
long (*fallocate)(struct file *file, int mode, loff_t offset,
loff_t len);
};
当应用程序使用open函数打开某个设备时,设备驱动程序的file_operations结构中的open成员函数会被调用。从这个角度来说,编写字符设备驱动程序就是为硬件的file_operations结构编写各个函数。
copy_from_user()和copy_to_user()
static inline unsigned long __must_check copy_from_user(void *to, const void __user *from, unsigned long n)
从用户空间得到数据
eg:
write传入的参数需要被copy_from_user从用户空间取出后才能使用
static inline unsigned long __must_check copy_to_user(void __user *to, const void *from, unsigned long n)
把数据传递给用户空间
eg:
同上read读取的参数,需要copy_to_user从内核中传出后才能read到
ioremap和iounmap
linux驱动直接操作不了内核,需要使用虚拟地址去映射,使用函数
static inline void __iomem *ioremap(phys_addr_t offset, unsigned long size)
phys_addr_t offset:物理地址
unsigned long size:虚拟地址
static inline void iounmap(void __iomem *addr)
module_init、module_exit和MODULE_LICENSE("GPL")
module_init、module_exit:指明驱动程序的初始化函数和卸载函数
MODULE_LICENSE("GPL"):遵循的协议
主次设备号
在PC上执行ls /dev/ttyS0 -l可以看到
crw-rw---- 1 root dialout 4, 64 3月 11 16:10 /dev/ttyS0
c表示/dev/ttyS0是一个字符设备。它的主设备号是4,次设备号是64。如果开头是b则为块设备
3.代码解析
Makefile
KERN_DIR = /work/system/linux-2.6.22.6
#KERN_DIR 内核的目录,需要先编译
all:
make -C $(KERN_DIR) M=`pwd` modules
#-C:进入KERN_DIR目录中去执行make
clean:
make -C $(KERN_DIR) M=`pwd` modules clean
rm -rf modules.order
obj-m += first_drv.o
#产生一个first_drv.o的模块
first_drv.c
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/delay.h>
#include <asm/uaccess.h>
#include <asm/irq.h>
#include <asm/io.h>
#include <asm/arch/regs-gpio.h>
#include <asm/hardware.h>
static struct class *firstdrv_class;
static struct class_device *firstdrv_class_dev;
volatile unsigned long *gpfcon = NULL;
volatile unsigned long *gpfdat = NULL;
static int first_drv_open(struct inode *inode, struct file *file)
{
//printk("first_drv_open
");
/* 配置GPF4,5,6为输出 */
*gpfcon &= ~((0x3<<(4*2)) | (0x3<<(5*2)) | (0x3<<(6*2)));
*gpfcon |= ((0x1<<(4*2)) | (0x1<<(5*2)) | (0x1<<(6*2)));
return 0;
}
static ssize_t first_drv_write(struct file *file, const char __user *buf, size_t count, loff_t * ppos)
{
int val;
//printk("first_drv_write
");
//write传入的参数需要使用copy_from_user把其从用户空间中取到内核
copy_from_user(&val, buf, count); // copy_to_user();
if (val == 1)
{
// 点灯
*gpfdat &= ~((1<<4) | (1<<5) | (1<<6));
}
else
{
// 灭灯
*gpfdat |= (1<<4) | (1<<5) | (1<<6);
}
return 0;
}
static struct file_operations first_drv_fops = {
.owner = THIS_MODULE, /* 这是一个宏,推向编译模块时自动创建的__this_module变量 */
.open = first_drv_open,
.write = first_drv_write,
};
int major;
static int first_drv_init(void)
{
major = register_chrdev(0, "first_drv", &first_drv_fops); // 注册, 告诉内核
//创建设备文件
firstdrv_class = class_create(THIS_MODULE, "firstdrv");
firstdrv_class_dev = class_device_create(firstdrv_class, NULL, MKDEV(major, 0), NULL, "xyz"); /* /dev/xyz */
gpfcon = (volatile unsigned long *)ioremap(0x56000050, 16);
gpfdat = gpfcon + 1;
return 0;
}
static void first_drv_exit(void)
{
unregister_chrdev(major, "first_drv"); // 卸载
class_device_unregister(firstdrv_class_dev);
class_destroy(firstdrv_class);
iounmap(gpfcon);
}
module_init(first_drv_init);
module_exit(first_drv_exit);
MODULE_LICENSE("GPL");
firstdrvtest.c
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
/* firstdrvtest on
* firstdrvtest off
*/
int main(int argc, char **argv)
{
int fd;
int val = 1;
fd = open("/dev/xyz", O_RDWR);
if (fd < 0)
{
printf("can't open!
");
}
if (argc != 2)
{
printf("Usage :
");
printf("%s <on|off>
", argv[0]);
return 0;
}
if (strcmp(argv[1], "on") == 0)
{
val = 1;
}
else
{
val = 0;
}
write(fd, &val, 4);
return 0;
}