// SPDX-License-Identifier: GPL-2.0

  #include <linux/fs.h>
  #include <linux/init.h>
  #include <linux/proc_fs.h>
  #include <linux/seq_file.h>
  
  static int devinfo_show(struct seq_file *f, void *v)
  {
  	int i = *(loff_t *) v;

  	if (i < CHRDEV_MAJOR_MAX) {

  		if (i == 0)

  			seq_puts(f, "Character devices:
  ");

  		chrdev_show(f, i);
  	}
  #ifdef CONFIG_BLOCK
  	else {

  		i -= CHRDEV_MAJOR_MAX;

  		if (i == 0)

  			seq_puts(f, "
  Block devices:
  ");

  		blkdev_show(f, i);
  	}
  #endif
  	return 0;
  }
  
  static void *devinfo_start(struct seq_file *f, loff_t *pos)
  {

  	if (*pos < (BLKDEV_MAJOR_MAX + CHRDEV_MAJOR_MAX))

  		return pos;
  	return NULL;
  }
  
  static void *devinfo_next(struct seq_file *f, void *v, loff_t *pos)
  {
  	(*pos)++;

  	if (*pos >= (BLKDEV_MAJOR_MAX + CHRDEV_MAJOR_MAX))

  		return NULL;
  	return pos;
  }
  
  static void devinfo_stop(struct seq_file *f, void *v)
  {
  	/* Nothing to do */
  }
  
  static const struct seq_operations devinfo_ops = {
  	.start = devinfo_start,
  	.next  = devinfo_next,
  	.stop  = devinfo_stop,
  	.show  = devinfo_show
  };

  static int __init proc_devices_init(void)
  {

  	proc_create_seq("devices", 0, NULL, &devinfo_ops);

  	return 0;
  }

  fs_initcall(proc_devices_init);