LXR linux/drivers/md/dm-zero.c

   1/*
   2 * Copyright (C) 2003 Jana Saout <jana@saout.de>
   3 *
   4 * This file is released under the GPL.
   5 */
   6
   7#include <linux/device-mapper.h>
   8
   9#include <linux/module.h>
  10#include <linux/init.h>
  11#include <linux/bio.h>
  12
  13#define DM_MSG_PREFIX "zero"
  14
  15/*
  16 * Construct a dummy mapping that only returns zeros
  17 */
  18static int zero_ctr(struct dm_target *ti, unsigned int argc, char **argv)
  19{
  20        if (argc != 0) {
  21                ti->error = "No arguments required";
  22                return -EINVAL;
  23        }
  24
  25        /*
  26         * Silently drop discards, avoiding -EOPNOTSUPP.
  27         */
  28        ti->num_discard_bios = 1;
  29
  30        return 0;
  31}
  32
  33/*
  34 * Return zeros only on reads
  35 */
  36static int zero_map(struct dm_target *ti, struct bio *bio)
  37{
  38        switch (bio_op(bio)) {
  39        case REQ_OP_READ:
  40                if (bio->bi_opf & REQ_RAHEAD) {
  41                        /* readahead of null bytes only wastes buffer cache */
  42                        return DM_MAPIO_KILL;
  43                }
  44                zero_fill_bio(bio);
  45                break;
  46        case REQ_OP_WRITE:
  47                /* writes get silently dropped */
  48                break;
  49        default:
  50                return DM_MAPIO_KILL;
  51        }
  52
  53        bio_endio(bio);
  54
  55        /* accepted bio, don't make new request */
  56        return DM_MAPIO_SUBMITTED;
  57}
  58
  59static struct target_type zero_target = {
  60        .name   = "zero",
  61        .version = {1, 1, 0},
  62        .module = THIS_MODULE,
  63        .ctr    = zero_ctr,
  64        .map    = zero_map,
  65};
  66
  67static int __init dm_zero_init(void)
  68{
  69        int r = dm_register_target(&zero_target);
  70
  71        if (r < 0)
  72                DMERR("register failed %d", r);
  73
  74        return r;
  75}
  76
  77static void __exit dm_zero_exit(void)
  78{
  79        dm_unregister_target(&zero_target);
  80}
  81
  82module_init(dm_zero_init)
  83module_exit(dm_zero_exit)
  84
  85MODULE_AUTHOR("Jana Saout <jana@saout.de>");
  86MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros");
  87MODULE_LICENSE("GPL");
  88