字符设备驱动之循环缓冲队列+读写等待

 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);  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> int main(int argc, char **argv) {  int fd;  char buf[10];  int i;  if (argc != 2)  {   printf("Usage: \n");   printf("%s string\n", argv[0]);   return 0;  }  fd = open("/dev/buffer", O_WRONLY);  write(fd, argv[1], strlen(argv[1]));   return 0; }