字符设备驱动之循环缓冲队列+读写等待

最新推荐文章于 2025-01-17 11:00:03 发布

WinCao90

最新推荐文章于 2025-01-17 11:00:03 发布

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CC 4.0 BY-SA版权

文章标签： buffer module struct class file user

本文链接：https://blog.youkuaiyun.com/yicao821/article/details/6775314

本文介绍了一段使用Linux内核实现的缓冲区读写操作代码，包括初始化、读取和写入等功能，并通过两个示例程序演示了如何在用户空间和内核空间进行交互。

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buffer.c

#include <linux/fs.h>
#include <linux/module.h>
#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/cdev.h>
#include <linux/ioport.h>
#include <linux/pci.h>
#include <asm/uaccess.h>
#include <asm/io.h>
#include <asm/irq.h>
#include <linux/interrupt.h>
#include <asm/mach/irq.h>
#include <asm/arch/regs-gpio.h>

static int major = 0;
static struct class *cls;

#define BUF_LEN 10
static char kern_buf[BUF_LEN];
static volatile int r = 0, w = 0;

static wait_queue_head_t read_waitq;
static wait_queue_head_t write_waitq;

static int isEmpty(void)
{
return (r == w);
}

static int isFull(void)
{
return (r == ((w+1)%BUF_LEN));
}

static int putData(char val)
{
if (isFull())
{
  return -1;
}
else
{
  kern_buf[w] = val;
  w = (w+1)%BUF_LEN;
  return 0;
}
}

static int getData(char *p)
{
if (isEmpty())
{
  return -1;
}
else
{
  *p = kern_buf[r];
  r = (r+1)%BUF_LEN;
  return 0;
}
}

ssize_t buffer_read(struct file *file, char __user *buf, size_t size, loff_t *offset)
{
int i = 0;
char val;

do {

wait_event_interruptible(read_waitq, !isEmpty());

  while ((i < size) && getData(&val) == 0)
  {
   copy_to_user(buf+i, &val, 1);
   wake_up_interruptible(&write_waitq);
   i++;
  }

} while (i < size);

return size;
}

ssize_t buffer_write(struct file *file, const char __user *buf, size_t size, loff_t *offset)
{
int i = 0;
char val;

do {

wait_event_interruptible(write_waitq, !isFull());

  while ((i < size) && !isFull())
  {
   copy_from_user(&val, buf+i, 1);
   putData(val);
   i++;
   wake_up_interruptible(&read_waitq);
  }

} while (i < size);

return size;
}

static struct file_operations buffer_fops = {
.owner   = THIS_MODULE,
.read    = buffer_read,
.write   = buffer_write,
};

int buffer_init(void)
{
major = register_chrdev(0, "buffer", &buffer_fops);

/* sysfs ==> 挂接到/sys */
cls = class_create(THIS_MODULE, "buffer_class");
class_device_create(cls, NULL, MKDEV(major, 0), NULL, "buffer");

// mdev会根据/sys下的这些内容创建/dev/buffer
init_waitqueue_head(&read_waitq);
init_waitqueue_head(&write_waitq);

return 0;
}
void buffer_exit(void)
{
unregister_chrdev(major, "buffer");

class_device_destroy(cls, MKDEV(major, 0));
class_destroy(cls);
}

module_init(buffer_init);
module_exit(buffer_exit);

MODULE_LICENSE("GPL");

reader.c

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

int main(int argc, char **argv)
{
int fd;
char buf[10];
int i;

fd = open("/dev/buffer", O_RDONLY);

read(fd, buf, 10);

printf("data: ");
for (i = 0; i < 10; i++)
printf("%c ", buf[i]);
printf("\n");

return 0;
}

writer.c

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>

/* writer string */
int main(int argc, char **argv)
{
int fd;
char buf[10];
int i;