text: #include <linux/errno.h>
  #include <linux/miscdevice.h>	/* for misc_register, and SYNTH_MINOR */
  #include <linux/types.h>
  #include <linux/uaccess.h>
  
  #include "speakup.h"
  #include "spk_priv.h"
  
  #ifndef SYNTH_MINOR
  #define SYNTH_MINOR 25
  #endif
  
  static int misc_registered;
  static int dev_opened;
  
  static ssize_t speakup_file_write(struct file *fp, const char __user *buffer,
  				  size_t nbytes, loff_t *ppos)
  {
  	size_t count = nbytes;
  	const char __user *ptr = buffer;
  	size_t bytes;
  	unsigned long flags;
  	u_char buf[256];
  
  	if (!synth)
  		return -ENODEV;
  	while (count > 0) {
  		bytes = min(count, sizeof(buf));
  		if (copy_from_user(buf, ptr, bytes))
  			return -EFAULT;
  		count -= bytes;
  		ptr += bytes;
  		spin_lock_irqsave(&speakup_info.spinlock, flags);
  		synth_write(buf, bytes);
  		spin_unlock_irqrestore(&speakup_info.spinlock, flags);
  	}
  	return (ssize_t) nbytes;
  }
  
  static ssize_t speakup_file_read(struct file *fp, char __user *buf,
  				 size_t nbytes, loff_t *ppos)
  {
  	return 0;
  }
  
  static int speakup_file_open(struct inode *ip, struct file *fp)
  {
  	if (!synth)
  		return -ENODEV;
  	if (xchg(&dev_opened, 1))
  		return -EBUSY;
  	return 0;
  }
  
  static int speakup_file_release(struct inode *ip, struct file *fp)
  {
  	dev_opened = 0;
  	return 0;
  }
  
  static const struct file_operations synth_fops = {
  	.read = speakup_file_read,
  	.write = speakup_file_write,
  	.open = speakup_file_open,
  	.release = speakup_file_release,
  };
  
  static struct miscdevice synth_device = {
  	.minor = SYNTH_MINOR,
  	.name = "synth",
  	.fops = &synth_fops,
  };
  
  void speakup_register_devsynth(void)
  {
  	if (misc_registered != 0)
  		return;
  /* zero it so if register fails, deregister will not ref invalid ptrs */
  	if (misc_register(&synth_device))
  		pr_warn("Couldn't initialize miscdevice /dev/synth.\n");
  	else {
  		pr_info("initialized device: /dev/synth, node (MAJOR %d, MINOR %d)\n",
  			MISC_MAJOR, SYNTH_MINOR);
  		misc_registered = 1;
  	}
  }
  
  void speakup_unregister_devsynth(void)
  {
  	if (!misc_registered)
  		return;
  	pr_info("speakup: unregistering synth device /dev/synth\n");
  	misc_deregister(&synth_device);
  	misc_registered = 0;
  }
  