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dm-zero.c

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

#include "dm.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;
      }

      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)
{
      int r = dm_unregister_target(&zero_target);

      if (r < 0)
            DMERR("unregister failed %d", r);
}

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");

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