/*
   * Copyright (C) 2003 Christophe Saout <christophe@saout.de>
   *
   * This file is released under the GPL.
   */

  #include <linux/device-mapper.h>

  
  #include <linux/module.h>
  #include <linux/init.h>
  #include <linux/bio.h>

  #define DM_MSG_PREFIX "zero"

  /*
   * Construct a dummy mapping that only returns zeros
   */
  static int zero_ctr(struct dm_target *ti, unsigned int argc, char **argv)
  {
  	if (argc != 0) {

  		ti->error = "No arguments required";

  		return -EINVAL;
  	}

  	/*
  	 * Silently drop discards, avoiding -EOPNOTSUPP.
  	 */
  	ti->num_discard_requests = 1;

  	return 0;
  }
  
  /*
   * Return zeros only on reads
   */
  static int zero_map(struct dm_target *ti, struct bio *bio,
  		      union map_info *map_context)
  {
  	switch(bio_rw(bio)) {
  	case READ:
  		zero_fill_bio(bio);
  		break;
  	case READA:
  		/* readahead of null bytes only wastes buffer cache */
  		return -EIO;
  	case WRITE:
  		/* writes get silently dropped */
  		break;
  	}

  	bio_endio(bio, 0);

  
  	/* accepted bio, don't make new request */

  	return DM_MAPIO_SUBMITTED;

  }
  
  static struct target_type zero_target = {
  	.name   = "zero",
  	.version = {1, 0, 0},
  	.module = THIS_MODULE,
  	.ctr    = zero_ctr,
  	.map    = zero_map,
  };

  static int __init dm_zero_init(void)

  {
  	int r = dm_register_target(&zero_target);
  
  	if (r < 0)

  		DMERR("register failed %d", r);

  
  	return r;
  }

  static void __exit dm_zero_exit(void)

  {

  	dm_unregister_target(&zero_target);

  }
  
  module_init(dm_zero_init)
  module_exit(dm_zero_exit)
  
  MODULE_AUTHOR("Christophe Saout <christophe@saout.de>");
  MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros");
  MODULE_LICENSE("GPL");