drivers/md/dm-zero.c

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