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 <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  */
  18 static 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         return 0;
  26 }
  27
  28 /*
  29  * Return zeros only on reads
  30  */
  31 static int zero_map(struct dm_target *ti, struct bio *bio,
  32                       union map_info *map_context)
  33 {
  34         switch(bio_rw(bio)) {
  35         case READ:
  36                 zero_fill_bio(bio);
  37                 break;
  38         case READA:
  39                 /* readahead of null bytes only wastes buffer cache */
  40                 return -EIO;
  41         case WRITE:
  42                 /* writes get silently dropped */
  43                 break;
  44         }
  45
  46         bio_endio(bio, 0);
  47
  48         /* accepted bio, don't make new request */
  49         return DM_MAPIO_SUBMITTED;
  50 }
  51
  52 static struct target_type zero_target = {
  53         .name   = "zero",
  54         .version = {1, 0, 0},
  55         .module = THIS_MODULE,
  56         .ctr    = zero_ctr,
  57         .map    = zero_map,
  58 };
  59
  60 static int __init dm_zero_init(void)
  61 {
  62         int r = dm_register_target(&zero_target);
  63
  64         if (r < 0)
  65                 DMERR("register failed %d", r);
  66
  67         return r;
  68 }
  69
  70 static void __exit dm_zero_exit(void)
  71 {
  72         dm_unregister_target(&zero_target);
  73 }
  74
  75 module_init(dm_zero_init)
  76 module_exit(dm_zero_exit)
  77
  78 MODULE_AUTHOR("Christophe Saout <christophe@saout.de>");
  79 MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros");
  80 MODULE_LICENSE("GPL");